Distribution of ascariasis, trichuriasis and hookworm infections in Ogun State, Southwestern Nigeria.

BACKGROUND: Ascariasis, Trichuriasis and Hookworm infections poses a considerable public health burden in Sub-Saharan Africa, and a sound understanding of their spatial distribution facilitates to better target control interventions. This study, therefore, assessed the prevalence of the trio, and mapped their spatial distribution in the 20 administrative regions of Ogun State, Nigeria.
METHODS: Parasitological surveys were carried out in 1,499 households across 33 spatially selected communities. Fresh stool samples were collected from 1,027 consenting participants and processed using ether concentration method. The locations of the communities were georeferenced using a GPS device while demographic data were obtained using a standardized form. Data were analysed using SPSS software and visualizations and plotting maps were made in ArcGIS software.
RESULTS: Findings showed that 19 of the 20 regions were endemic for one or more kind of the three infections, with an aggregated prevalence of 17.2%. Ascariasis was the most frequently observed parasitic infection in 28 communities with a prevalence of 13.6%, followed by hookworm infections with a prevalence of 4.6% while Trichuriasis was the least encountered with a prevalence of 1.7%. The spatial distribution of infections ranges between 5.3-49.2% across the regions. The highest and lowest distribution of overall helminth infections was recorded in Egbado South and Egbado North respectively. Nine regions had infection status between 20.0%-49.2%, while 10 regions had infection status between 5.3%-15.8%.
CONCLUSION: This study provides epidemiological data on the prevalence and spatial distribution of ascariasis, trichuriasis and hookworm infections which will add to the baseline data and guide the public health officers in providing appropriate control strategies in the endemic communities.

Background

Infections with Ascaris lumbricoides (Ascariasis), Trichuris trichiura (Trichuriasis) and hookworms (Ancyclostomiasis / Necatoriasis) are widely distributed in tropical and subtropical areas, with the greatest numbers occurring in sub-Saharan Africa, the Americas, China and East Asia [1]. Transmission of these parasites is prominent in areas with favorable climatic and environmental conditions, poor access to potable water supply, sanitation and hygiene resources [2]. Recent estimates shows that more than 5 billion people are at risk, and about 1.5 billion people are currently infected [1]. Besides, about 267 million pre-schoolers (age 2–5 years) and 568 million school-aged children (age 5–14 years) who live in areas where these parasites are intensively transmitted are at risk [3]. These children suffer the major brunt of these infections, with leading clinical manifestations such as malnutrition and iron deficiency anemia [4]. In addition, children co-infected with these parasites show impaired cognitive and physical development leading to significant reductions in educational gains via inefficient learning and other school achievements [5,6]. Nonetheless, in most endemic settings, there is an established morbidity control programme targeted at school-aged children due to high worm burden as a result of their frequent contact with contaminated soils, and exposure to poor sanitation and unhygienic conditions [7,8]. The World Health Organization through this programme recommends large-scale administration of albendazole, either once a year (annually) when the baseline prevalence of infections is between 20 and 50%, or twice a year (biannually) when the prevalence is above 50% [7]. This strategy costs donor agencies and developing economies billions of dollar every year. However, in resource challenged settings where there are records of sporadic large-scale administration of anthelmintic drugs, there is need to constantly delineate endemic areas, and provide robust maps to identify hot spots. Such maps are essential to facilitate better targeting and efficient delivery of cost effective control interventions [9]. This study therefore mapped the spatial distribution of Ascariasis, Trichuriasis and Hookworm infections in Ogun State, southwestern Nigeria.

Methods

Study area

Ogun State is situated in the southwestern part of Nigeria and is made up of 20 administrative local government areas (LGAs) with Abeokuta as the capital city. The state has a landmass of 16,085 km2, and is located within longitude 2°45¹E and 3°55¹E and latitude 7°01¹N and 7°18¹N. The State is highly urbanized, with a population estimate of about 5million inhabitants, an annual growth rate of 2.83%, and about 95% of the inhabitants are of the Yoruba tribe. The State covers a wide range of vegetation zones, from the freshwater swamp with mangrove forest in the southeast, through diverse forest communities to the woody guinea savannah in the northwestern tip of the state. The rain forest is the largest ecological zone running through the centre of the state from east to west. Annual rainfall ranges from 900mm in the northern parts, up to 1600 mm along the coast. Major occupations of the population are farming, timber logging, and trading. Primary schools exist in most communities but in some cases, two or more communities share the same school.

Study design and sampling procedures

This is a cross-sectional and community-based study, conducted between July 2016 and November 2018. Systematic point sampling method was employed in selection of sampling sites to ensure an unbiased and fair representation of communities across the 20 administrative LGAs in the State. As an initial step in the selection process, a 15 km x 15 km sized grid was placed on the administrative map of Ogun state in Google Earth (GE) software using the GE path tool. The centre of each grid was located in Arc GIS 9.3 software, and the geographical coordinates were recorded. The closest community to the centre of each grid was identified and selected using Google Earth software. A total of 33 communities were selected across the 20 LGAs in the state as the study communities (S1 Dataset).

Selection of households for survey

A total sampling method was employed for household selection in the communities surveyed. Prior to data collection, selected communities were visited and with the permission of the community leaders, meetings were held with the members of the community to intimate them about the purpose of the study and the procedures to be adopted. Every member of the household is eligible for participating in the research. In each community, a house, usually at the centre of the community was designated as an area of work for processing and microscopic examination of stool samples. The location of the communities was georeferenced with Garmin 20.0 GPS device.

Ethical approval and consent to participate

Ethical clearance for this study (HPRS/381/183) was obtained from the Ethics review committee of Department of Planning, Research and Statistics, Ogun State Ministry of Health, Oke Imosan Abeokuta, Nigeria. For each household visited, consent forms were made available to household members after explaining the objectives of the research to them. Members willing to participate in the research and who completed written consent froms were enrolled into the study. However, for children below age sixteen, consent was provided by their parents after completing an assent form on their behalf.

Faecal samples collections and processing

A stool container was distributed to consenting participants in each of the georeferenced household. Participants’ unique identifiers were marked on the containers and detailed instructions of how to collect a fresh morning stool sample were given. Individuals who consented to take part in the study were requested to provide stool up to half (about 5gm) into the labelled plastic bottles provided. Stool samples were processed using the SAF- Ether (Sodium acetate-acetic acid formalin—ether) concentration method in the designated area of work within the community. One gram (1g) of the faecal sample was emulsified in already prepared 10 ml of SAF in another sample bottle. The bottle was covered and shaken vigorously to form a cloudy suspension. The stool suspension was strained into a centrifuge tube using double gauze of about 13 mm diameter placed in a funnel. The residue was discarded while the filtrate was centrifuged at 2000 rpm for 1 minute. The supernatant was decanted. 7 ml of normal saline was later added to the sediment, after which 3 ml of ether was finally added to the suspension [10]. A stopper was placed on the tube, and the mixture was shaken vigorously before centrifuging for 5 minutes at 2000 rpm. The first three layers of the suspension observed after centrifuging was discarded, leaving the last layer of sediment. This sediment was then pipetted on a clean microscopic slide. Two slides were prepared from 1g of each stool sample by experienced laboratory technicians 2 hours post sample collection [10].

Estimation of parasite’s prevalence and intensity

Prepared slides were examined under a compound microscope for microscopic ova or larva of the three parasites (Ascaris spp., Trichuris spp. and Hookworms). The parasites’ eggs were counted for each species, and number of eggs per species and per stool examined was recorded for each participant. Mean infection intensity estimates were computed for each examined person on a logarithmic scale for the purpose of data normalization i.e. EPG = Log (n +1), where EPG means egg per gram.

Data management, analysis and visualizations

Data obtained during the survey i.e. demographics, were first subjected to descriptive analysis in SPSS 20.0 software, and results were reported in frequencies and percentages. Prevalence and intensity estimates of helminth infections were also computed for each of the communities surveyed and reported accordingly. Significance level was set at P≤0.05. Data were imported into ArcGIS 9.3 software for visualizations and plotting maps.

Results

Sex and age distribution of study participants

A total of 1499 participants comprising of 899 (60%) females and 600 (40%) males were enrolled across the 33 communities in 20LGAs out of which 1024 (68.5%) returned stool samples for laboratory analysis. The sex ratio of females to males was 3:2. The ages of the enrolled participants are provided in Table 1.

Table 1

Sex and age distribution of study participants.

SN	LGA		Sex (%)		Age in years (%)
		Number Examined	Male	Female	<5yrs	5-15yrs	16-25yrs	26-40yrs	41-70yrs	>70yrs
1	Abeokuta north	87	28(32.2)	59(67.8)	7(8.0)	64(7.6)	9(10.3)	3(3.4)	4(4.6)	0(0)
2	Abeokuta south	20	11(55.0)	9(45.0)	0(0)	0(0)	6(30.0)	4(20.0)	10(50.0)	0(0)
3	Ado-odo ota	84	32(38.1)	52(61.9)	0(0)	1(1.2)	12(14.3)	23(27.4)	43(51.2)	5(6.0)
4	Ewekoro	61	23(37.7)	38(62.3)	0(0)	21(34.4)	10(16.4)	15(24.6)	15(24.6)	0(0)
5	Ifo	37	13(35.1)	24(64.9)	0(0)	0(0)	3(8.1)	17(45.9)	15(40.5)	2(5.4)
6	Ijebu east	71	34(47.9)	37(52.1)	0(0)	2(2.8)	12(16.9)	23(32.4)	30(42.3)	4(5.6)
7	Ijebu north	54	35(64.8)	19(35.2)	0(0)	1(1.9)	2(3.7)	17(31.5)	23(42.6)	11(20.4)
8	Ijebu north-east	27	15(55.6)	12(44.4)	0(0)	0(0)	0(0)	4(14.8)	12(44.4)	11(40.7)
9	Ijebu ode	46	17(37.0)	29(63.0)	0(0)	0(0)	6(13.0)	23(50.0)	1(28.3)	4(8.7)
10	Ikenne	39	18(46.2)	21(53.8)	1(2.6)	13(33.3)	4(10.3)	7(17.9)	10(25.6)	4(10.3)
11	Imeko-afon	90	31(34.4)	59(65.6)	1(1.1)	17(18.9)	16(17.8)	28(31.1)	23(25.6)	5(5.6)
12	Ipokia	42	20(47.6)	22(52.4)	0(0)	1(2.4)	9(21.4)	17(40.5)	14(33.3)	1(2.4)
13	Obafemi-owode	89	35(39.3)	54(60.7)	0(0)	1(1.1)	16(18.0)	34(38.2)	31(34.8)	7(7.9)
14	Odeda	108	54(50.0)	54(50.0)	0(0)	4(3.7)	10(9.3)	37(34.3)	45(41.7)	12(11.1)
15	Odogbolu	77	22(28.6)	55(71.4)	0(0)	3(3.9)	3(3.9)	21(27.3)	41(53.2)	9(11.7)
16	Ogun waterside	126	41(32.5)	85(67.5)	0(0)	2(1.6)	6(4.8)	55(43.7)	54(42.9)	9(7.1)
17	Remo north	22	7(31.8)	15(68.2)	0(0)	0(0)	1(4.5)	10(45.5)	9(40.9)	2(9.1)
18	Shagamu	168	30(17.9)	138(82.1)	1(0.6)	21(12.5)	12(7.1)	46(27.4)	80(47.6)	8(4.8)
19	Egbado north	156	99(63.5)	57(36.5)	4(2.6)	5(3.2)	13(8.3)	42(26.9)	83(53.2)	9(5.8)
20	Egbado south	95	35(36.8)	60(63.2)	0(0)	5(5.3)	6(6.3)	28(29.5)	54(56.8)	2(2.1)
	Total	1499	600(40.0)	899(60.0)	14(0.9)	161(10.7)	156(10.4)	454(30.3)	609(40.6)	105(7.0)

Spatial distribution of Ascaris, Trichuris and hookworm infections in Ogun State

Fig 1 shows the spatial distribution of the three parasites’ in Ogun State. Of the 20 LGAs examined, 19(95.0%) were endemic for one or more of the three parasite. Ascaris lumbricoides are the most geographically distributed, found in 28(84.8%) out of the 33 communities and 19(95.0%) out of 20LGAs. Hookworm was present in 19(57.6%) out of 33 communities and 15(75.0%) out of 20LGAs. Trichuris trichiura infections were found in 9(27.3%) out of 33 communities and 7(35.0%) out of 20LGAs.

Fig 1

Spatial distribution of Ascaris, Trichuris and hookworm infections in Ogun State.

Source: The authors using their primary data in ArcGIS software created this map. Permission: The authors give permission to re-use this map.

Co-distribution patterns of Ascaris, Trichuris and hookworm infections in Ogun State

Fig 2 shows the co-distribution patterns of STH infections in the State. Single infection was recorded for Ascaris lumbricoides in 3 LGAs; Ewekoro, Ikenne and Ijebu northeast. For double infections, combination of Ascaris and Hookworm were the most predominant, observed in 15 LGAs except Ewekoro, Ijebu east, Ijebu northeast, Ikenne and Ijebu ode. Combination of Ascaris and Trichuris co-distribution was recorded in 7 LGAs; Egbado north, Egbado south, Ado-odo ota, Ijebu east, Ipokia, Obafemi owode and Ogun waterside, while combination of Trichuris and hookworm was recorded in 6 LGAs; Ado-odo ota, Ipokia, Obafemi owode, Ogun waterside, Egbado north and Egbado south. Triple infections comprising Ascaris, Trichuris and hookworm was recorded in 6 LGAs (Table 2).

Fig 2

Venn diagram showing the co-distribution of Ascaris, Trichuris and hookworm infections in Ogun State.

The numbers in the venn diagram reflects the number of affected LGAs. Source: The authors using their primary data in ArcGIS software created this map. Permission: The authors give permission to re-use this map.

Table 2

Prevalence estimates for Ascaris, Trichuris and hookworm infections in Ogun State.

SN	LGA	NCE	NSE	A. lumbricoides NP (%)	T. Trichiura NP (%)	Hookworm NP (%)	Any STH NP (%)
1	Abeokuta North	1	40	7(17.5)	0(0)	1(2.5)	8(20.0)
2	Abeokuta South	1	14	5(37.5)	0(0)	1(7.1)	6(42.9)
3	Ado-odo ota	2	56	6(10.7)	4(7.1)	2(3.6)	8(14.3)
4	Ewekoro	1	46	3(6.5)	0(0)	0(0)	3(6.5)
5	Ifo	1	19	5(26.3)	0(0)	3(15.8)	7(36.8)
6	Ijebu East	2	38	6(15.8)	1(2.6)	0(0)	6(15.8)
7	Ijebu North	2	48	6(12.5)	0(0)	1(2.1)	6(12.5)
8	Ijebu North-East	1	26	4(15.4)	0(0)	0(0)	4(15.4)
9	Ijebu Ode	1	25	0(0)	0(0)	0(0)	0(0)
10	Ikenne	1	36	11(30.6)	0(0)	0(0)	11(30.6)
11	Imeko-Afon	2	86	4(4.7)	0(0)	2(2.3)	5(5.8)
12	Ipokia	1	13	4(30.8)	3(23.1)	2(15.4)	5(38.5)
13	Obafemi-Owode	3	54	15(27.8)	4(7.4)	9(16.7)	22(40.7)
14	Odeda	2	71	4(5.6)	0(0)	6(8.5)	8(11.3)
15	Odogbolu	1	54	6(11.1)	0(0)	1(1.9)	7(13.0)
16	Ogun waterside	2	85	16(18.8)	1(1.2)	5(5.9)	20(23.5)
17	Remo North	1	15	4(26.7)	0(0)	2(13.3)	6(40.0)
18	Shagamu	2	128	9(7.0)	0(0)	3(2.3)	10(7.8)
19	Egbado North	4	114	3(2.6)	1(0.9)	2(1.8)	6(5.3)
20	Egabdo South	2	59	22(37.3)	3(5.1)	7(11.9)	29(49.2)
	Total	33	1027	140(13.6)	17(1.7)	47(4.6)	177(17.2)
	Df			19	19	19	19
	Chi-square			95.325	73.24	54.68	131.097
	P-value			0.00	0.00	0.00	0.00

NCS = number of communities sampled, NSE = number of stools examined, NP = number positive Df = Degree of freedom.

Aggregated prevalence of Ascaris, Trichuris and hookworm infections in Ogun State

An aggregated prevalence of 17.2% was recorded for at least one infection of Ascaris lumbricoides, Trichuris trichiura or hookworm. The prevalence range was between 5.3–49.2% across the LGAs. The highest prevalence was recorded in Egbado South while the lowest was recorded in Egbado North, however, no infection was recorded in Ijebu-Ode (Fig 3). Of the 19 endemic LGAs, 9 had prevalence status ranging between 20.0%-49.2% and 10 LGAs had prevalence status ranging between 5.3%-15.8%. There were significant differences in the prevalence record for any STH species across the 19 endemic LGAs (P = 0.000) (Fig 4).

Fig 3

Aggregated prevalence of Ascaris, Trichuris and hookworm infections in Ogun State.

Source: The authors using their primary data in ArcGIS software created this map. Permission: The authors give permission to re-use this map.

Fig 4

LGAs classification by WHO prevalence thresholds for preventive chemotherapy.

Source: The authors using their primary data in ArcGIS software created this map. Permission: The authors give permission to re-use this map.

Specific prevalence estimates for Ascaris, Trichuris and hookworm infections in Ogun State

By species’ prevalence, an overall prevalence of 13.6% was recorded for Ascaris lumbricoides, followed by hookworm with 4.6% and Trichuris trichiura with 1.7% (Table 2). The lowest prevalence for the three infections were observed in Egbado north., while Abeokuta south, Obafemi owode and Ipokia recorded the highest prevalence for ascariasis, hookworm infections and trichuriasis respectively (Table 2). Spatial-wise, Ascaris lumbricoides was the most predominant, found in 28(84.8%) communities (Fig 5), followed by hookworm in 19 (57.6%) communities (Fig 6) and Trichuris trichiura in 9(27.3%) communities (Fig 7). There were significant differences in the prevalence record for each parasitic infection across the endemic LGAs (P = 0.000).

Fig 5

Spatial distribution of Ascaris lumbricoides infection in Ogun State, Nigeria.

Source: The authors using their primary data in ArcGIS software created this map. Permission: The authors give permission to re-use this map.

Fig 6

Spatial distribution of hookworm infections in Ogun State, Nigeria.

Source: The authors using their primary data in ArcGIS software created this map. Permission: The authors give permission to re-use this map.

Fig 7

Spatial distribution of Trichuris trichiura infections in Ogun State, Nigeria.

Source: The authors using their primary data in ArcGIS software created this map. Permission: The authors give permission to re-use this map.

Aggregated and specific mean intensity estimates for Ascaris, Trichuris and hookworm infections in Ogun State

Table 3 shows the intensity estimates for Ascaris, Trichuris and hookworm infections in Ogun state. The aggregated geometric mean intensity of infections was 0.14±0.01epg with mean intensity ranging from 0.03±0.01epg to 0.43±0.06epg across the LGAs. The aggregated intensity shows that worm loads were highest in Obafemi owode and lowest in Imeko-afon. By species intensities, Ascaris lumbricoides infection intensity was the highest with, 0.11±0.01epg, followed by hookworm with 0.03±0.01epg and Trichuris trichiura with 0.01±0.00epg. Ascaris mean intensities range between 0.01±0.01epg and 0.32±0.05epg, with the lowest in Imeko afon and highest in Ifo and Egbado south. For Hookworm infection, intensities range between 0.01±0.00epg and 0.13±0.04epg, with the lowest in Ijebu north, Egbado north, Egbado south, Ogun waterside, Imeko afon and highest in Obafemi-owode. Trichuris mean intensities range between 0.01±0.01epg and 0.10±0.05epg with the highest load in Ipokia and the lowest in Ogun waterside, Ijebu east and Egbado north.

Table 3

Intensity (Mean ± SEM) of Ascaris, Trichuris and hookworm infections in selected population in Ogun State.

SN	LGA	NCS	NSE	A. lumbricoides Mean epg ± SEM	T. Trichiura Mean epg ± SEM	Hookworm Mean epg ± SEM	Any STH Mean epg ± SEM
1	Abeokuta north	1	40	0.19±0.08	0.00±0.00	0.03±0.03	0.22±0.08
2	Abeokuta south	1	14	0.18±0.07	0.00±0.00	0.00±0.00	0.21±0.07
3	Ado-odo ota	2	56	0.09±0.03	0.00±0.00	0.05±0.02	0.14±0.05
4	Ewekoro	1	46	0.05±0.03	0.00±0.00	0.00±0.00	0.05±0.03
5	Ifo	1	19	0.32±0.13	0.00±0.00	0.12±0.07	0.41±0.13
6	Ijebu east	2	38	0.10±0.04	0.01±0.01	0.00±0.00	0.11±0.04
7	Ijebu north	2	48	0.09±0.04	0.00±0.00	0.01±0.01	0.09±0.04
8	Ijebu north east	1	26	0.20±0.11	0.00±0.00	0.00±0.00	0.20±0.11
9	Ijebu ode	1	25	0.00±0.00	0.00±0.00	0.00±0.00	0.00±0.00
10	Ikenne	1	36	0.20±0.60	0.00±0.00	0.00±0.00	0.20±0.06
11	Imeko-afon	2	86	0.01±0.01	0.00±0.00	0.01±0.01	0.03±0.01
12	Ipokia	1	13	0.15±0.07	0.10±0.05	0.04±0.03	0.23±0.09
13	Obafemi-owode	3	54	0.31±0.07	0.04±0.02	0.13±0.04	0.45±0.07
14	Odeda	2	71	0.07±0.03	0.00±0.00	0.10±0.04	0.14±0.05
15	Odogbolu	1	54	0.04±0.01	0.00±0.00	0.02±0.02	0.06±0.02
16	Ogun waterside	2	85	0.14±0.03	0.01±0.01	0.01±0.01	0.15±0.03
17	Remo north	1	15	0.14±0.06	0.00±0.00	0.04±0.02	0.18±0.06
18	Shagamu	2	128	0.05±0.02	0.00±0.00	0.01±0.01	0.06±0.02
19	Egbado north	4	114	0.02±0.01	0.01±0.01	0.01±0.00	0.04±0.01
20	Egbado south	2	59	0.32±0.05	0.04±0.02	0.08±0.03	0.43±0.06
	Total	33	1027	0.11±0.01	0.01±0.00	0.03±0.01	0.14±0.01

NCS = number of communities sampled, NSE = number of stools examined, epg = egg per gram of faeces, SEM = Standard Error of Mean

Prevalence of Ascaris, Trichuris and hookworm infections infection by sex and age characteristics

Table 4 shows the prevalence of infection by sex and age distribution of study participants. Majority of those infected were females 122(18.8%), although there were no significant differences in prevalence estimates across sex (P > 0.05). By age category, majority of those infected were adults and with age above 26 years, however there were no significant differences in prevalence of infection across age category (P > 0.05).

Table 4

Prevalence of STH infections in relation to sex and age in selected population.

LGA	NE	A. lumbricoides NP (%)	T. Trichiura NP (%)	Hookworm NP (%)	Any STH NP (%)
Sex
Male	430	50(11.6)	9(2.1)	18(4.2)	65(15.1)
Female	597	90(15.1)	8(1.3)	29(4.9)	112(18.8)
Total	1027	140(13.6)	17(1.7)	47(4.6)	177(17.2)
P value		0.112	0.351	0.611	0.127
Df		1	1	1	1
Chi square		2.523	0.871	0.258	2.327
Age group in years
<5	11	2(18.2)	0(0)	0(0)	2(18.2)
5–15	110	15(13.6)	0(0)	3(2.7)	17(15.5)
16–25	101	11(10.9)	2(2.0)	2(2.0)	13(12.9)
26–40	317	45(14.2)	7(2.2)	18(5.7)	61(19.2)
41–70	422	57(13.5)	7(1.7)	22(5.2)	74(17.5)
>70	66	10(15.2)	1(1.5)	2(3.0)	10(15.2)
Total	1027	140(13.6)	17(1.7)	47(4.6)	177(17.2)
P value		0.958	0.745	0.469	0.743
Df		5	5	5	5
Chi square		1.058	2.705	4.582	2.723

Df = degree of freedom

Discussion

In Nigeria, research findings on the geospatial distribution of Ascaris, Trichuris and Hookworm infections are scarce, but emerging [11,12,13]. This study therefore adds to the wealth of existing epidemiological data on the prevalence and distribution of these infections in Ogun State, Nigeria. However, no attempt was made to analyse for risk factors. The overall prevalence recorded in this study (17.2%) is in line with the predictions of 13.8% and <20% prevalence reported by Oluwole et al. [11] and Yaro et al. [13] respectively. The prevalence values of the three soil transmitted helminth (STH) infections recorded in this study is comparable with the findings of Mogaji et al. [2], Oluwole et al. [12] and Gemechu et al. [14]. The similarities observed supports existing presumptions on decreasing trend of STH infections due to on-going chemotherapy programmes in most endemic SSA countries [15,16]. However, aggregated estimates at the state-level may unnecessarily mask the spatial patterns of disease distribution at LGA and communities, hence misleading intervention programmes and public health decisions. This peculiar dynamics of STH morbidity supports the need for intensified public health efforts in delineating localized hotspots and intervening appropriately to curtail the menace.

The prevalence recorded for Ascaris lumbricoides infections in this study is comparable with findings from previous epidemiological surveys [12,17]. The increase in prevalence of A. lumbricoides infection as observed in 19 of the 20 LGAs studied is similar to the findings of Oluwole et al [12] with respect to spatial pattern of A. lumbricoides. This may be due to similar ecological factors such as soil moisture, pH or temperature, which favours the transmission of STHs in the areas of study. The moderate prevalence of less than 20% recorded in various communities in contrast with prevalence of more than 50% reported by Oluwole et al. [12] may be due to the difference in the composition of population studied. Over 40% of the respondents in this study were adults within the age range 41-70years, as compared to 100% school-aged children population in the report of Oluwole et al. [12]. The school-aged children are known to be the most vulnerable to STH infections, and infections tend to be higher among this group than any other subset in the community due to their risky behaviours that predisposes them to infection. Nevertheless, the findings from this study give a more complete population-based picture of current infection patterns that may exist in endemic communities, as infections may also cluster in households (adults) rather than school unit (children) only [18,19,20,21].

Trichuris trichiura has a restricted distribution in Ogun State. In fact, the prevalence of this parasite has been consistently reported to be low and non-existent in many parts of the country [2,11,12,13,17,22]. As such the low prevalence of 1.7% reported in this study is expected, and the geo-spatial restrictions of Trichuris trichiura ova to the southern part of the state may have been due to favourable environmental conditions [11]. In addition, there are similarities in the spatial distribution of Trichuris observed in this study with that reported by Oluwole et al. [12].

Hookworm infections is the second most common infection recorded in this study, with peak prevalence’s reported among the adult respondents. This observation is in line with already established fact that prevalence and intensities of hookworm infections are restricted to adult populations [22]. However, the prevalence recorded in this study (4.6%) is lower than those reported by Mogaji et al. [2]; Oluwole et al. [12] and Fafunwa et al. [23] where prevalence estimate within the range 7.1–26.2% was observed. Nevertheless, the prevalence is higher than the 4.13% reported by Sam-wobo et al. [16]. The disparities observed across these studies maybe due to differences in study area/population, seasonality, soil parameters, environmental variables and socioeconomic status. In addition, walking barefooted which is a major risk factor in the percutaneous transmission of hookworm parasites is a common feature of school-aged children. The low prevalence recorded for hookworm infections may therefore be attributed to the fact that school-aged children constitutes only 10% of the study population.

Conclusion

This study has shown the distribution of Ascaris, Trichuris and hookworm infections in Ogun State, Nigeria. These results and maps are useful and can serve as decision support tools for targeting, planning and delivery of intervention programmes aimed at controlling STH morbidity.

(XLSX)

Click here for additional data file.

25 Mar 2020

PONE-D-20-06434

Spatial Distribution of Ascariasis, Trichuriasis and Hookworm Infections in Ogun State, Southwestern Nigeria.

PLOS ONE

Dear Dr Mogaji,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

ACADEMIC EDITOR: The study results provided some useful information, the spatial distributions of STH could be evaluated in a better/clearer way. I suggest the author modify the spatial analysis and map presentations and re-submit the revised version. Attached, 2 independent reviewers have some suggestions for your consideration.

==============================

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Additional Editor Comments (if provided):

The study results provided some useful information, the spatial distributions of STH could be evaluated in a better/clearer way. I suggest the author modify the spatial analysis and map presentations and re-submit the revised version.

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Reviewer #2: Yes

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Reviewer #1: The manuscript entitled “Spatial Distribution of Ascariasis, Trichuriasis and Hookworm Infections in Ogun State, Southwestern Nigeria” investigated STH infections in Ogun State and try to mapped the spatial distribution of STH infection. Though the study results provided some useful information, the spatial distributions of STH could be evaluated in a better/clearer way. I suggest the author modify the spatial analysis and map presentations and re-submit the revised version. Below are some comments:

Major issues:

1. It seems that the georeferenced household’s information was not analyzed in the study because the figure only showed the locations of the selected communities. Since you have more than thousand georeferenced households participated in your study, why don’t you apply interpolation techniques (e.g. kriging or kernel density) to evaluate the prevalence and intensity?

2. The range of different age groups are different (e.g. 16-25, 41-70), any reason for the grouping criteria? The age distributions could be biased.

3. The investigation has been done at community level; however, the results were still presented at LGA level, and it’s hard to identify where is the most prevalent area. For instance, I have no idea where is “Yewa South” on the map (the LGA with the highest prevalence rate). Please modify the map presentation in a better way.

4. This is a cross-sectional survey which might be affected by many other factors. For example, does the infection prevalence influence by any intervention activities? Such limitation should be discussed in the manuscript.

5. Though the overall prevalence is not very high in the study area, the transmission still varied by locations. Can you explain why “Yewa South” has the highest prevalence?

Minor issue:

1. The scale bar in Figure 1 is not correct. It should not be “millimeters.” Please check whether you apply a correct projection coordination system.

2. Table 1 can be moved to the supplementary materials.

3. Figure 5. What does “Ogun State” mean in the legend? For the legend indicated the LGA with no case, please add the border.

Reviewer #2: Specific comments

Abstract

Result section

Line 2-4: The sentences “Ascariasis was the most spatially distributed found in 28 communities, with 140(13.6%) infected subjects, followed byHookworm infection in 19 communities, with 47(4.6%) infected subjects and Trichuriasis in 9 communities, with 17(1.7%) infected subjects.”

should be reconstructed to read “ Ascariasis was the most frequently observed parasite in 28 communities with a prevalence of 13.6%, followed by hookworm with a prevalence of 4.6% while Trichuris was the least encountered with a prevalence of 1.7%.

Line 6-7: The sentence is incomplete “The highest and lowest distribution of what (?) was recorded in Yewa South and Yewa North respectively.

Line 8: Delete the phrase “By WHO preventive chemotherapy thresholds”

Conclusion

This study provides information on the prevalence and spatial risk of Ascariasis, Trichuriasis

and Hookworm infection that will serve as decision-support tool to help facilitate targeting of

control interventions.

The conclusion should be re-written as “ This study provides epidemiological data on the prevalence and spatial distribution of ascariasis , trichuriasis and hookworm infection which will add to the baseline data and guide the public health officers in providing appropriate control strategies in the endemic communities.

Background

Line 7-8: Replace the phrases in parentheses (children between age 2 and 5) and (children between age 5 and 14) with (age 2-5 years) and (age 5-14 years).

Line 15: The sentence “there is an established morbidity control programme targeted at school-aged children due to their high level of contact with soils” should be re-written as “there is an established morbidity control programme targeted at school-aged children due to high worm burden as a result of their frequent contact with contaminated soils, ……………………….

Methods

Study area

Line 10: The phrase “The major occupation of the population is……………… should be re-phrased as “Major occupations of the population are………………

Study design and sampling technique

Line 1: The sentence “This study was community-based and cross-sectional in design” should be re-written as “This is a cross-sectional and community-based study”.

Selection of households for survey

Line 2: The sentence “communities were visited and sensitized about the study procedures

and were openly invited to participate in the research through community meetings and town

announcers” should be replaced with “selected communities were visited and with the permission of the community leaders, meetings were held with the members of the community to intimate them about the purpose of the study and the procedures to be adopted”.

The sub title “Collection of faecal samples and parasitological diagnosis” be replaced with “ Faecal samples collections and processing”.

Line 3-4: The sentence “All participants were asked to provide a sufficiently large stool sample (at least 5 g)” should be replaced with “Individuals who consented to take part in the study were requested to provide stool up to half (about 5gm) into the labelled plastic bottles provided.

Line 6: Delete the word “Precisely”.

Line 7-8: The sentence “The bottle was covered and agitated vigorously to suspend the stool efficiently in the solution” be replaced with “The bottle was covered and shaken vigorously to form a cloudy suspension”.

Line 9: Delete the word “further”

Line 11: The sentence “The supernatant was also discarded after centrifuging” be replaced with “The supernatant was decanted”.

Line 12-14: The sentence “7 ml of normal saline was later added to the sediment, after which 3 ml of ether was finally added to the suspension”. ( I did not agree with this procedure, it is faulty). The deposit or residue obtained after decanting the supernatant should be resuspended in distilled water or saline of a known vol and shaking vigorously. Thereafter, an equal vol of ether will then be added (i.e if 3ml of distilled water or saline was used to resuspend the residue, 3ml of ether should then be added). The authors should correct this procedure.

Results

The sentence “A total of 1,499 respondents were subsequently enrolled after consent across the 33 communities and 20 LGAs. However, only 1,027 (68.5%) of them consented to the provision

of adequate stool samples (~5g) for laboratory analysis for parasites’ ova or larva. By

demography, 899(60.0%) were females and 600(40.0%) were males” should be rewritten as “ A total of 1499 participants comprising of 899 (60%) females and 600 (40%) males were enrolled across the 33 communities in 20LGAs out of which 1024 (68.5%) returned stool samples for laboratory analysis.

The sentence “The sex ratio of females to males was 3:2. In addition, the highest number of respondents were within the age range 41-70yrs (40.6%), followed by 26-40yrs (30.3%), 5-15yrs (10.7%), 16-25yrs (10.4%) and >70yrs (7.0%) (Table 2)” should be re-written as “The ages of the enrolled participants are provided in table 2.

Co-distribution patterns of Ascaris, Trichuris and Hookworm infections in Ogun State

Line1: Replace the words “mono infection” with single infection

Line 2: Delete the word “only”

Line 3: Replace the word “co-distribution” with the word “combination”

Line 5: Begin with combination of Ascaris and Trichuris and delete the word “co-distribution”

Line 6 & 7: Rewrite “while Trichuris and Hookworm co-distribution was recorded in 6 LGAs;” as “while combination of Trichuris and hookworm was……………………….”

Line 8-10: Rewrite “However, for triple infections, the three species (Ascaris, Trichuris and Hookworm) were co-distributed in 6 LGAs; Ado-Odo, Ipokia, Obafemi-Owode, Ogun waterside, Yewa North and Yewa South” as “ Triple infection comprising Ascaris, Trichuris and hookworm was recorded in 6 LGAs (table 3)”.

The sentences “The aggregated prevalence of 17.2% was recorded for at least one infection of Ascaris lumbricoides, Trichuris trichiura or hookworm. The prevalence range was between 5.3 –

49.2% across the LGAs (Figure 4). Infections were highest in Yewa south, lowest in Yewa

north and no infection was recorded in Ijebu-Ode. Of the 19 endemic LGAs, 9 had prevalence

status ranging between 20.0%-49.2% (Abeokuta north, Abeokuta south, Ifo, Ikenne, Ipokia,

Obafemi owode, Ogun waterside, Remo north and Yewa south” should be reduced to “ The highest prevalence of 49.2% was recorded in Yewa South while the lowest of 5.3% was recorded in Yewa North, however, no infection was recorded in Ijebu-Ode.

Delete this sentence “However, 10 LGAs haprevalence status ranging between 5.3%-15.8% which is below the WHO recommended thresholds for preventive chemotherapy (Ado-odo ota, Ewekoro, Ijebu east, Ijebu north, Ijebu north east, Imeko afon, Odeda, Odogbolu, Sagamu and Yewa north).

Specific prevalence estimates for Ascaris, Trichuris and Hookworm infections in Ogun

State.

The contents under this section is too wordy. The authors should highlight significant findings in terms of the most frequently encountered parasite in each LGA, the range of other parasites and if there is significant differences in prevalence of infection across the communities.

Aggregated and specific mean intensity estimates for Ascaris, Trichuris and Hookworm

infections in Ogun State.

The authors should express the intensity as eggs per gram (epg) of faeces i.e epg should be put in front of the mean intensity values in all cases.

The authors stated under this section about the single, doubleand triple infections, however there was no dat presented to show the prevalences of this infection. The table should be provided.

Discussion.

The authors should use simple grammar to discuss their findings.

**********

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Reviewer #1: No

Reviewer #2: No

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Submitted filename: Comments on the reviewed MS.docx

Click here for additional data file.

2 Apr 2020

PONE-D-20-06434

Spatial Distribution of Ascariasis, Trichuriasis and Hookworm Infections in Ogun State, Southwestern Nigeria.

PLOS ONE

ACADEMIC EDITOR: The study results provided some useful information, the spatial distributions of STH could be evaluated in a better/clearer way. I suggest the author modify the spatial analysis and map presentations and re-submit the revised version. Attached, 2 independent reviewers have some suggestions for your consideration.

Response: Thank you very much for this observation. We will like to inform you that the objective of this present study is to provide epidemiological data on STH morbidity in the state, using household data, rather than school-based data. These data are useful for assessing the impact of school-based STH control on community prevalence. Households data were grouped into community data, and then aggregated at LGA level. The LGA is the implementation unit for school-based preventive chemotherapy programme in the state. Spatial analysis of the household data are still under analysis, and it not part of this report. As such, not to mislead the reviewers, we have removed the word spatial from the title to reflect the current analysis.

Reviewer 1:

Reviewer #1: The manuscript entitled “Spatial Distribution of Ascariasis, Trichuriasis and Hookworm Infections in Ogun State, Southwestern Nigeria” investigated STH infections in Ogun State and try to mapped the spatial distribution of STH infection. Though the study results provided some useful information, the spatial distributions of STH could be evaluated in a better/clearer way. I suggest the author modify the spatial analysis and map presentations and re-submit the revised version. Below are some comments:

Major issues:

C1. It seems that the georeferenced household’s information was not analyzed in the study because the figure only showed the locations of the selected communities. Since you have more than thousand georeferenced households participated in your study, why don’t you apply interpolation techniques (e.g. kriging or kernel density) to evaluate the prevalence and intensity?

R1: Thank you very much for this observation. We will like to inform you that the objective of this present study is to provide epidemiological data on STH morbidity in the state, using household data, rather than school-based data. These data are useful for assessing the impact of school-based STH control on community prevalence. Households data were grouped into community data, and then aggregated at LGA level. The LGA is the implementation unit for school-based preventive chemotherapy programme in the state. Spatial analysis of the household data are still under analysis, and it not part of this report. As such, not to mislead the reviewers, we have removed the word spatial from the title to reflect the current analysis.

C2. The range of different age groups are different (e.g. 16-25, 41-70), any reason for the grouping criteria? The age distributions could be biased.

R2: We intended to understand the dynamics of STH morbidity that may exist among the different age classes, i.e. preschoolers (<5yrs), School-aged children (5-15years), 16-25years (post-primary), youth (26-40 years), 40-70 (Adults), and aged (>70 years). Only the age classes 5-15 years are under preventive chemotherapy in the State.

C3. The investigation has been done at community level; however, the results were still presented at LGA level, and it’s hard to identify where is the most prevalent area. For instance, I have no idea where is “Yewa South” on the map (the LGA with the highest prevalence rate). Please modify the map presentation in a better way.

R3: Yes, the investigations were done at household level in the selected communities. However, results were presented both at the community level and LGA level.

For instance, the maps created (Figure 5, 6 and 7) show the spatial distribution of the parasites at the community level (i.e. the points on the map refers to communities)

However, the map (Figure 4) shows the aggregated prevalence of STH infection by LGA.

To avoid the presentation of cumbersome tables, results presented in tables were summarized at the LGA level. The LGA level is quite important as it remains the focal point for planning/delivery of MDA in the state.

In addition, we realized that Yewa-north and Yewa south are not reflected in the maps. This is because these LGAs are also known as Egbado North and Egbado South respectively. We have thus adjusted our text to reflect Egbado North and Egbado South.

C4. This is a cross-sectional survey which might be affected by many other factors. For example, does the infection prevalence influence by any intervention activities? Such limitation should be discussed in the manuscript.

R4: Thank you very much. We have included this limitation in our discussion (Line 273-275)

This study therefore adds to the wealth of existing epidemiological data on the prevalence and distribution of these infections in Ogun State, Nigeria. However, no attempt was made to analyse for risk factors.

C5. Though the overall prevalence is not very high in the study area, the transmission still varied by locations. Can you explain why “Yewa South” has the highest prevalence?

R5: The southern region of the state has been characterized to have favorable environmental conditions that allow STH parasites to thrive. This coupled with other socio-economic factors may have contributed to the high prevalence recorded.

Minor issue:

C6: The scale bar in Figure 1 is not correct. It should not be “millimeters.” Please check whether you apply a correct projection coordination system.

R6: We have to removed Figure 1 since it is less informative. And more importantly we have four figures showing the study area already. Thank you.

C7: Table 1 can be moved to the supplementary materials.

R7: Thank you very much. We have moved it to supplementary materials as suggested.

C8: Figure 5. What does “Ogun State” mean in the legend? For the legend indicated the LGA with no case, please add the border.

R8: Thank you very much. We have removed Ogun State from the legend. We have also included the border for the LGA with zero prevalence.

Reviewer 2 Comments:

Reviewer #2: Specific comments

Abstract

Result section

C1: Line 2-4: The sentences “Ascariasis was the most spatially distributed found in 28 communities, with 140(13.6%) infected subjects, followed by Hookworm infection in 19 communities, with 47(4.6%) infected subjects and Trichuriasis in 9 communities, with 17(1.7%) infected subjects.” should be reconstructed to read “ Ascariasis was the most frequently observed parasite in 28 communities with a prevalence of 13.6%, followed by hookworm with a prevalence of 4.6% while Trichuris was the least encountered with a prevalence of 1.7%.

R1: We have modified our text as suggested. Please find the improved text in between lines 45-48. Thanks

C2: Line 6-7: The sentence is incomplete “The highest and lowest distribution of what (?) was recorded in Yewa South and Yewa North respectively.

R2: We have improved our text.

Line 49: The highest and lowest distribution of overall helminth infections was recorded in Egbado South and Egbado North respectively

C3: Line 8: Delete the phrase “By WHO preventive chemotherapy thresholds”

R3: The phrase has been deleted as suggested.

Line 50-51: Nine regions had infection status between 20.0%-49.2%, while 10 regions had infection status between 5.3%-15.8%.

Conclusion

C4: This study provides information on the prevalence and spatial risk of Ascariasis, Trichuriasis and Hookworm infection that will serve as decision-support tool to help facilitate targeting of control interventions.

The conclusion should be re-written as “ This study provides epidemiological data on the prevalence and spatial distribution of ascariasis , trichuriasis and hookworm infection which will add to the baseline data and guide the public health officers in providing appropriate control strategies in the endemic communities.

R4: We have modified our text as suggested. Please find the improved text in between lines 53-56. Thanks

Line 53-56: This study provides epidemiological data on the prevalence and spatial distribution of ascariasis , trichuriasis and hookworm infections which will add to the baseline data and guide the public health officers in providing appropriate control strategies in the endemic communities.

Background

C5: Line 7-8: Replace the phrases in parentheses (children between age 2 and 5) and (children between age 5 and 14) with (age 2-5 years) and (age 5-14 years).

R5: We have modified our text as suggested. Please find the improved text in between lines 66-67. Thanks

Line 66-67: Besides, about 267 million pre-schoolers (age 2-5 years) and 568 million school-aged children (age 5-14 years) who live in areas where these

C6: Line 15: The sentence “there is an established morbidity control programme targeted at school-aged children due to their high level of contact with soils” should be re-written as “there is an established morbidity control programme targeted at school-aged children due to high worm burden as a result of their frequent contact with contaminated soils, ……………………….

R6: We have modified our text as suggested. Please find the improved text in between lines 72-74. Thanks

Lines 72-74: Nonetheless, in most endemic settings, there is an established morbidity control programme targeted at school-aged children due to high worm burden as a result of their frequent contact with contaminated soils

Methods

Study area

C7: Line 10: The phrase “The major occupation of the population is……………… should be re-phrased as “Major occupations of the population are………………

R7: We have modified our text as suggested. Please find the improved text in between lines 96. Thanks

Line 96: Major occupations of the population are farming, timber logging, and trading.

Study design and sampling technique

C8: Line 1: The sentence “This study was community-based and cross-sectional in design” should be re-written as “This is a cross-sectional and community-based study”.

R8: We have modified our text as suggested. Please find the improved text in between lines 101-102. Thanks

Line 101-102: This is a cross-sectional and community-based study, conducted between July 2016 and November 2018.

Selection of households for survey

C9: Line 2: The sentence “communities were visited and sensitized about the study procedures and were openly invited to participate in the research through community meetings and town announcers” should be replaced with “selected communities were visited and with the permission of the community leaders, meetings were held with the members of the community to intimate them about the purpose of the study and the procedures to be adopted”.

R9: We have modified our text as suggested. Please find the improved text in between lines 113-115. Thank you so much.

Line 113-115: Prior to data collection, selected communities were visited and with the permission of the community leaders, meetings were held with the members of the community to intimate them about the purpose of the study and the procedures to be adopted.

C10: The sub title “Collection of faecal samples and parasitological diagnosis” be replaced with “ Faecal samples collections and processing”.

R10: We have modified our text as suggested. Please find the improved text in line 122. Thank you

Line 122: Faecal samples collections and processing

C11: Line 3-4: The sentence “All participants were asked to provide a sufficiently large stool sample (at least 5 g)” should be replaced with “Individuals who consented to take part in the study were requested to provide stool up to half (about 5gm) into the labelled plastic bottles provided.

R11: We have modified our text as suggested. Please find the improved text in between lines 125-127. Thank you so much.

Lines 125-127: Individuals who consented to take part in the study were requested to provide stool up to half (about 5gm) into the labelled plastic bottles provided.

C12: Line 6: Delete the word “Precisely”.

R12: Deleted as suggested. Please check Line 129

C13: Line 7-8: The sentence “The bottle was covered and agitated vigorously to suspend the stool efficiently in the solution” be replaced with “The bottle was covered and shaken vigorously to form a cloudy suspension”.

R13: We have modified our text as suggested. Please find the improved text in between lines 130-131. Thank you so much.

Line 130-131: The bottle was covered and shaken vigorously to form a cloudy suspension. The stool suspension……

C14: Line 9: Delete the word “further”

R14: Deleted as suggested.

Line 131: The stool suspension was strained into…..

C15: Line 11: The sentence “The supernatant was also discarded after centrifuging” be replaced with “The supernatant was decanted”.

R15: We have modified our text as suggested. Please find the improved text in line 133. Thank you

Line 133: The supernatant was decanted

C16: Line 12-14: The sentence “7 ml of normal saline was later added to the sediment, after which 3 ml of ether was finally added to the suspension”. ( I did not agree with this procedure, it is faulty). The deposit or residue obtained after decanting the supernatant should be resuspended in distilled water or saline of a known vol and shaking vigorously. Thereafter, an equal vol of ether will then be added (i.e if 3ml of distilled water or saline was used to resuspend the residue, 3ml of ether should then be added). The authors should correct this procedure.

R16: Thank you for this explanation. However, we followed the procedure describe by Endriss et al. 2005. We have included the reference immediately after the text.

Results

C17: The sentence “A total of 1,499 respondents were subsequently enrolled after consent across the 33 communities and 20 LGAs. However, only 1,027 (68.5%) of them consented to the provision of adequate stool samples (~5g) for laboratory analysis for parasites’ ova or larva. By demography, 899(60.0%) were females and 600(40.0%) were males” should be rewritten as “ A total of 1499 participants comprising of 899 (60%) females and 600 (40%) males were enrolled across the 33 communities in 20LGAs out of which 1024 (68.5%) returned stool samples for laboratory analysis.

R17: We have modified our text as suggested. Please find the improved text in between lines 161-163. Thank you so much.

Line 161-163: A total of 1499 participants comprising of 899 (60%) females and 600 (40%) males were enrolled across the 33 communities in 20LGAs out of which 1024 (68.5%) returned stool samples for laboratory analysis.

C18: The sentence “The sex ratio of females to males was 3:2. In addition, the highest number of respondents were within the age range 41-70yrs (40.6%), followed by 26-40yrs (30.3%), 5-15yrs (10.7%), 16-25yrs (10.4%) and >70yrs (7.0%) (Table 2)” should be re-written as “The ages of the enrolled participants are provided in table 2.

R18: We have modified our text as suggested. Please find the improved text in between lines 130-131. Thank you so much.

Line 163-164: The ages of the enrolled participants are provided in table 1.

C19-24: Co-distribution patterns of Ascaris, Trichuris and Hookworm infections in Ogun State

C19: Line1: Replace the words “mono infection” with single infection

C20: Line 2: Delete the word “only”

C21: Line 3: Replace the word “co-distribution” with the word “combination”

C22: Line 5: Begin with combination of Ascaris and Trichuris and delete the word “co-distribution”

C23: Line 6 & 7: Rewrite “while Trichuris and Hookworm co-distribution was recorded in 6 LGAs;” as “while combination of Trichuris and hookworm was……………………….”

C24: Line 8-10: Rewrite “However, for triple infections, the three species (Ascaris, Trichuris and Hookworm) were co-distributed in 6 LGAs; Ado-Odo, Ipokia, Obafemi-Owode, Ogun waterside, Yewa North and Yewa South” as “ Triple infection comprising Ascaris, Trichuris and hookworm was recorded in 6 LGAs (table 3)”.

R19-24: We have considered all the corrections (C19-24) and modified our text accordingly to reflect them. Please find the improved text in between lines 173-182. Thank you so much

Line 173-182:

Co-distribution patterns of Ascaris, Trichuris and Hookworm infections in Ogun State

Figure 3 shows the co-distribution patterns of STH infections in the State. Single infection was recorded for Ascaris lumbricoides in 3 LGAs; Ewekoro, Ikenne and Ijebu northeast. For double infections, combination of Ascaris and Hookworm were the most predominant, observed in 15 LGAs except Ewekoro, Ijebu east, Ijebu northeast, Ikenne and Ijebu ode. Combination of Ascaris and Trichuris co-distribution was recorded in 7 LGAs; Yewa north, Yewa south, Ado-odo ota, Ijebu east, Ipokia, Obafemi owode and Ogun waterside, while combination of Trichuris and hookworm was recorded in 6 LGAs; Ado-odo ota, Ipokia, Obafemi owode, Ogun waterside, Yewa north and Yewa south. Triple infections comprising Ascaris, Trichuris and hookworm was recorded in 6 LGAs (Table 3).

C25: The sentences “The aggregated prevalence of 17.2% was recorded for at least one infection of Ascaris lumbricoides, Trichuris trichiura or hookworm. The prevalence range was between 5.3 – 49.2% across the LGAs (Figure 4). Infections were highest in Yewa south, lowest in Yewa north and no infection was recorded in Ijebu-Ode. Of the 19 endemic LGAs, 9 had prevalence

status ranging between 20.0%-49.2% (Abeokuta north, Abeokuta south, Ifo, Ikenne, Ipokia, Obafemi owode, Ogun waterside, Remo north and Yewa south” should be reduced to “ The highest prevalence of 49.2% was recorded in Yewa South while the lowest of 5.3% was recorded in Yewa North, however, no infection was recorded in Ijebu-Ode.

R25: We have considered the corrections and modified our text accordingly to reflect them. Please find the improved text in between lines 187-188.

The highest prevalence was recorded in Yewa South while the lowest was recorded in Yewa North, however, no infection was recorded in Ijebu-Ode (Figure 4).

C26: Delete this sentence “However, 10 LGAs haprevalence status ranging between 5.3%-15.8% which is below the WHO recommended thresholds for preventive chemotherapy (Ado-odo ota, Ewekoro, Ijebu east, Ijebu north, Ijebu north east, Imeko afon, Odeda, Odogbolu, Sagamu and Yewa north).

R26: We have considered the comments raised. We believe deleting this sentence will mask the pattern we are trying to showcase. Therefore we have modified our text accordingly to reflect them. Please find the improved text in between lines 188-191.

Of the 19 endemic LGAs, 9 had prevalence status ranging between 20.0%-49.2% and 10 LGAs had prevalence status ranging between 5.3%-15.8%. There were significant differences in the prevalence record for any STH species across the 19 endemic LGAs (P=0.000) (Figure 5).

Specific prevalence estimates for Ascaris, Trichuris and Hookworm infections in Ogun State.

C27: The contents under this section is too wordy. The authors should highlight significant findings in terms of the most frequently encountered parasite in each LGA, the range of other parasites and if there is significant differences in prevalence of infection across the communities.

R27: We have considered the suggestions raised and modified our text accordingly to reflect them. Please find the improved text in between lines 197-205

Specific prevalence estimates for Ascaris, Trichuris and Hookworm infections in Ogun State.

By species’ prevalence, an overall prevalence of 13.6% was recorded for Ascaris lumbricoides, followed by hookworm with 4.6% and Trichuris trichiura with 1.7% (Table 3). The lowest prevalence for the three infections were observed in Yewa north., while Abeokuta south, Obafemi owode and Ipokia recorded the highest prevalence for ascariasis, hookworm infections and trichuriasis respectively (Table 3). Spatial-wise, Ascaris lumbricoides was the most predominant, found in 28(84.8%) communities (Figure 6), followed by hookworm in 19 (57.6%) communities (Figure 7) and Trichuris trichiura in 9(27.3%) communities. There were significant differences in the prevalence record for each parasitic infection across the endemic LGAs (P=0.000).

.

Aggregated and specific mean intensity estimates for Ascaris, Trichuris and Hookworm infections in Ogun State.

C28: The authors should express the intensity as eggs per gram (epg) of faeces i.e epg should be put in front of the mean intensity values in all cases.

R28: We have considered the suggestions raised and modified our text accordingly to reflect them. Please find the improved text in between lines 221-234

Line 221-234

Aggregated and specific mean intensity estimates for Ascaris, Trichuris and Hookworm infections in Ogun State.

Table 4 shows the intensity estimates for Ascaris, Trichuris and hookworm infections in Ogun state. The aggregated geometric mean intensity of infections was 0.14±0.01epg with mean intensity ranging from 0.03±0.01epg to 0.43±0.06epg across the LGAs. The aggregated intensity shows that worm loads were highest in Obafemi owode and lowest in Imeko-afon. By species intensities, Ascaris lumbricoides infection intensity was the highest with, 0.11±0.01epg, followed by hookworm with 0.03±0.01epg and Trichuris trichiura with 0.01±0.00epg. Ascaris mean intensities range between 0.01±0.01epg and 0.32±0.05epg, with the lowest in Imeko afon and highest in Ifo and Yewa south. For Hookworm infection, intensities range between 0.01±0.00epg and 0.13±0.04epg, with the lowest in Ijebu north, Yewa north, Yewa south, Ogun waterside, Imeko afon and highest in Obafemi-owode. Trichuris mean intensities range between 0.01±0.01epg and 0.10±0.05epg with the highest load in Ipokia and the lowest in Ogun waterside, Ijebu east and Yewa north.

C31: The authors stated under this section about the single, double and triple infections, however there was no dat presented to show the prevalences of this infection. The table should be provided.

R31: A venn diagram was used to present the number of LGAs where single, double and triple infections could be found. Please see figure 3. We didn’t report specific combination prevalences in our text to reduce the number of tables.

Discussion.

C32: The authors should use simple grammar to discuss their findings.

R32: We have re-worked our discussion to enhance clarity. Please check Line 273-286

Submitted filename: Response to Reviewers_2.docx

Click here for additional data file.

27 Apr 2020

PONE-D-20-06434R1

Distribution of Ascariasis, Trichuriasis and Hookworm Infections in Ogun State, Southwestern Nigeria.

PLOS ONE

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Reviewer #2: Comments on the revised version of the MS

General comments: The authors revised the MS in line with the suggestions provided, however, there are still some minor corrections that needs to be effected in the discussion section.

Specific comments

Discussion

Line 283-284: The prevalence estimates also corroborates ………………………………….due to chemotherapy programmes in SSA countries (The statement is not clear). However, I would suggest that the sentence should be re-written to read “The prevalence values for the 3STHs recorded in this study is comparable ………………………………. (The values obtained should be compared with the findings of previous studies and may then give reason for the similarities or differences.).

Line 287: Replace the words “Sub-state level” with LGAs and communities

Line 292: Replace the following words “reported” with “recorded”; “corroborates” with “comparable”; “recent” with “previous”.

Line 293-295: The sentence “Ascaris lumbricoides infections were observed in …………………………………..by Oluwole et al. (12) should be recast to read “The increase in prevalence of A. lumbricoides infection as observed in 19 of the 20 LGAs studied is similar to the findings of Oluwole et al (12) with respect to spatial pattern of A. lumbricoides. This may be due to similar ecological factors (mention the factors) which favours the transmission of STHs in the areas of study”.

Line 296-299: Please delete the sentences “where moderate……………………………………… of STH parasites in the state”.

Line 300-302: The sentences “However, none of the LGAs studied has……………………. Population in the report of Oluwole et al. (12)” should be recast to read “The moderate prevalence of less than 20% recorded in various communities in contrast with prevalence of more than 50% reported by Oluwole et al. (12) may be due to the difference in the composition of population studied.

Line 313: Please delete the word “aggregate”

Line 316: Your assertion that hookworms egg can withstand extreme temp (I guess you meant extreme heat). Remember hookworm eggs have thin shells compared with thick shell of Ascaris eggs. It is only Ascaris eggs which can withstand adverse environmental conditions.

Line 317: Please replace the word ‘commonalities” with the word “similarities”

Line 326: replace the word “observed” with “reported”

Line 332: Replace the word “study” with “studied”

Table 3: The title should be rephrased to read “Intensity (Mean ± SEM) of Ascaris, hookworm and Trichuris infection in selected population in Ogun State”.

In table 3: Re-write the abbreviation “SE” as “SEM”. Define SEM as Standard Error of Mean

Table 4: The title should be rephrased to read "Prevalence of STH infections in relation to sex and age in selected population

Still in Table 4: Under Age group insert the word "Years" and delete the word "Years" from each age group.

**********

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28 Apr 2020

Reviewer #2: Comments on the revised version of the MS

General comments: The authors revised the MS in line with the suggestions provided, however, there are still some minor corrections that needs to be effected in the discussion section.

Specific comments

Discussion

C1: Line 283-284: The prevalence estimates also corroborates ………………………………….due to chemotherapy programmes in SSA countries (The statement is not clear). However, I would suggest that the sentence should be re-written to read “The prevalence values for the 3STHs recorded in this study is comparable ………………………………. (The values obtained should be compared with the findings of previous studies and may then give reason for the similarities or differences.).

R1: The corrections have been made as suggested. We have compared our prevalence values with three reports (2 from Nigeria and one from Ethiopia (Gemechu et al. 2020)

Please find our improved text between Line 283-287

The prevalence values of the three soil transmitted helminth (STH) infections recorded in this study is comparable with the findings of Mogaji et al. [2], Oluwole et al. [12] and Gemechu et al. [14]. The similarities observed supports existing presumptions on decreasing trend of STH infections due to on-going chemotherapy programmes in most endemic SSA countries [15,16].

C2: Line 287: Replace the words “Sub-state level” with LGAs and communities

R2: This correction has been made (Line 289). Thank you

C3: Line 292: Replace the following words “reported” with “recorded”; “corroborates” with “comparable”; “recent” with “previous”.

R3: This correction has been made.

Line 293-294: The prevalence recorded for Ascaris lumbricoides infections in this study is comparable with findings from previous epidemiological surveys [12,17].

C4: Line 293-295: The sentence “Ascaris lumbricoides infections were observed in …………………………………..by Oluwole et al. (12) should be recast to read “The increase in prevalence of A. lumbricoides infection as observed in 19 of the 20 LGAs studied is similar to the findings of Oluwole et al (12) with respect to spatial pattern of A. lumbricoides. This may be due to similar ecological factors (mention the factors) which favours the transmission of STHs in the areas of study”.

R4: The corrections have been made as suggested (Line 294-298)

The increase in prevalence of A. lumbricoides infection as observed in 19 of the 20 LGAs studied is similar to the findings of Oluwole et al [12] with respect to spatial pattern of A. lumbricoides. This may be due to similar ecological factors such as soil moisture, pH or temperature, which favours the transmission of STHs in the areas of study.

C5: Line 296-299: Please delete the sentences “where moderate……………………………………… of STH parasites in the state”.

R5: The sentences have been deleted. Thank you

C6: Line 300-302: The sentences “However, none of the LGAs studied has……………………. Population in the report of Oluwole et al. (12)” should be recast to read “The moderate prevalence of less than 20% recorded in various communities in contrast with prevalence of more than 50% reported by Oluwole et al. (12) may be due to the difference in the composition of population studied.

R6: The corrections have been made as suggested (Line 298-300)

The moderate prevalence of less than 20% recorded in various communities in contrast with prevalence of more than 50% reported by Oluwole et al. [12] may be due to the difference in the composition of population studied.

C7: Line 313: Please delete the word “aggregate”

R7: The word has been deleted. Thank you

C8: Line 316: Your assertion that hookworms egg can withstand extreme temp (I guess you meant extreme heat). Remember hookworm eggs have thin shells compared with thick shell of Ascaris eggs. It is only Ascaris eggs which can withstand adverse environmental conditions.

R8: Thank you for this comment. We have removed the line entirely to improve on clarity

C9: Line 317: Please replace the word ‘commonalities” with the word “similarities”

R9: The corrections have been made as suggested (Line 313)

C10: Line 326: replace the word “observed” with “reported”

R10: The corrections have been made as suggested (Line 317)

C11: Line 332: Replace the word “study” with “studied”

R11: The corrections have been made as suggested

C12: Table 3: The title should be rephrased to read “Intensity (Mean ± SEM) of Ascaris, hookworm and Trichuris infection in selected population in Ogun State”.

R12: The corrections have been made as suggested (Line 253)

C13: In table 3: Re-write the abbreviation “SE” as “SEM”. Define SEM as Standard Error of Mean

R13: The corrections have been made as suggested (Line 253-256)

C14: Table 4: The title should be rephrased to read "Prevalence of STH infections in relation to sex and age in selected population

R14: The corrections have been made as suggested (Line 264-266)

C15: Still in Table 4: Under Age group insert the word "Years" and delete the word "Years" from each age group.

R15: The corrections have been made as suggested (Line 264-266)

Submitted filename: Response to Reviewers comments.docx

Click here for additional data file.

6 May 2020

Distribution of Ascariasis, Trichuriasis and Hookworm Infections in Ogun State, Southwestern Nigeria.

PONE-D-20-06434R2

Dear Dr. Mogaji,

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PLOS ONE

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Reviewers' comments:

13 May 2020

PONE-D-20-06434R2

Distribution of Ascariasis, Trichuriasis and Hookworm Infections in Ogun State, Southwestern Nigeria.

Dear Dr. Mogaji:

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