Seasonal prevalence of trypanosomosis, Glossina density and infection along the escarpment of Omo River, Loma district, southern Ethiopia.

BACKGROUND: The temporal information of trypanosomosis and tsetse apparent density is very limited in the southern part of the country. So, the study was conducted to estimate the temporal, dry and wet seasons, prevalence of cattle trypanosomosis, and tsetse fly apparent density and its infection by trypanosome along the escarpment of Omo River, Loma district, Southern Ethiopia.
METHODS: A total of 964 cattle (482 in each seasons) were examined for trypanosomosis using buffy coat technique. For Glossina and biting flies study a total of 80 odor-baited, acetone and aged cow urine, NGU traps were deployed around the watering and grazing areas.
RESULTS: The overall prevalence of cattle trypanosomosis was 4.98% of which 3.1% and 6.8% accounted to dry and wet seasons, respectively. The prevalence of trypanosomosis was significantly higher during wet season (OR = 1.93, P < 0.05), in poor body condition (OR = 3.71, P < 0.05) and in black coat colour (OR = 13.18, P < 0.05) animals. Two species of Trypanosome, T. congolense and T. vivax, were circulating in the area both in dry and wet seasons. A total of 327 Glossina (126 G. pallidipes and 201 G. fuscipes) were traped by using odour baited 80 NGU traps. The overall apparent density of Glossina was 4.1 Flies/Trap/Day. Relatively higher Glossina/Trap/Day caught in wet season (4.9 Flies/Trap/Day) than dry season (3.3 Flies/Trap/Day). Two species of Glossina namely G. pallidipes and G. fuscipes were distributed in the study areas. From the flies caught 127 Glossina were randomly selected and dissected. The overall proportion of Glossina infection was 15% with higher proportion of infection in wet season (19.6%) than the dry season (11.3%). Higher infection proportion was observed in G. pallidipes.
CONCLUSION: Trypansomosis is the major challenge for cattle productivity in the district. So to reduce the impact trypanosomosis and Glossina active community participation can play a key role.

Introduction

Animal trypanosomosis is a lethal parasitic disease caused by unicellular protozoal organisms known as trypanosoma. Trypanosomes are flagellated protozoa that inhabit the extracellular compartment of host blood; and transmitted to mammals by blood sucking flies of the genus Glossina, commonly known as tsetse flies (Itard, 1989; Leak, 1999; Black and Seed, 2002). Trypanosomosis negatively impacted Africa's struggle against poverty; and it is endemic in more than thirty countries (Shallow, 2000). The major clinical manifestation of cattle trypanosomosis are intermittent fever, anaemia, dullness, anorexia, apathetic, watery occular discharge and superficial lymph nodes enlargement. The animals progressively become emaciated and cachectic, and die. In cows, irregular estrous cycle and abortion observed (Constable et al., 2017). Probably more than any other disease affecting livestock, trypanosomosis constrains agricultural production and causes food insecurity in vast and fertile swaths of sub-Saharan Africa (Holt et al., 2016).

In Ethiopia, animal trypanosomosis is widely distributed across the tsetse infested belts, which is found in Sub-Sharan Africa. In these regions, about 220,000 Km2 of fertile land is infested by Glossina spp. (Cecchi et al., 2008). In Ethiopia, about five Glossina spp. were reported: G. pallidipes, G. morsitans submorsitans, G. fuscipes fuscipes, G. tachinoides and G. longipennis. The most commonly reported and important Trypanosoma spp. affecting cattle in southern and south-western part of the country include T. congolense, T. vivax and T. brucei (Duguma et al., 2015; Abebe, 2005). Cattle production plays a key role in the livelihood of southern and western regions of Ethiopia; however, their production potential is not fully utilized due to endemic diseases like trypanosomosis (Abebe, 2005). Trypanosomosis is threatening the agricultural production and cattle breeding more severely than any other livestock disease (Moti et al., 2015).

Information on temporal and spatial dynamics of tsetse and trypanosomes remain limited and may be a reason that control strategies are less effective (Nnko et al., 2017). So knowledge of temporal, dry and wet season, prevalence of trypanosomosis and distribution of tsetse fly are important when devising appropriate strategies for the control of these problems (Van den Bossche and de Deken, 2002). The temporal information of trypanosomosis and tsetse apparent density is very limited in the southern part of the country. Therefore, this study was conducted to estimate the temporal, dry and wet season, prevalence of bovine trypanosomosis, to assess tsetse fly apparent density and its infection by trypanosome.

Materials and methods

Study area and animals

This study was done along the escarpment of Omo River, Loma district, southern Ethiopia. It is located along the Omo tsetse belt, and has an altitude 501–3300 m.a.s.l. that is located in south western Ethiopia. Geographically, the district is found between 6°34′120″ to 7°6′360″ North and 36°55′480'′ to 37°26′240″ East. The district is bordered on the south by Goffa Zone, on the west by Isara district, on the northwest by Maraka district, on the north by Gena Bosa district and on the east by the Wolaita Zone on the eastern and Omo River (Figure 1). The study area characterized by bimodal type of rainfall, the short rainy season (March to May) and the long (June to September). The annual rainfall and temperature of the area is ranged from 900 to 1800 mm and 14–30 °C, respectively (LDAR, 2018). From the district, the four study kebeles were selected purposively based on the level of complaint by animal owners about trypanosomosis. The selected four kebeles were Zima Waruma, Afuki Weyiro, Subo Tulama and Danaba Bolla, which are bordered by Omo river.

Figure 1

Map to show the study area.

The study animals were local breed zebu cattle above six months of age, which were kept by extensive management system. In the area, all animals above six months of age were left for free grazing; and hence, included into the study.

Study design, sample size and sampling

The study was conducted to estimate the seasonal prevalence of trypanosomosis and the apparent density of Glossina species and other blood sucking flies; moreover, to assess tsetse flies infection rate by trypanosome. This study was conducted from December 2018 to September 2019 that include dry (December to February) and wet (June August) season.

Repeated cross-sectional study design was employed to estimate the prevalence of trypanosomosis and to identify the Glossina species prevailing in the area both in dry and wet seasons. The sample size required for the study was computed by considering trypanosomosis prevalence of 26.8% reported by Teklebirhan et al. (2016), 95% confidence interval and 5% absolute precision. Then to improve the precision the sample size was increased by about 60%. So, a total of 964 animals selected for the study both in dry and wet season. Systematic random sampling technique as described by employed to select the study animals (Thrusfield, 2018). Potential risk factors considered in the study were season, body condition, sex, age and coat colour.

Study methodology

Parasitological study

The marginal ear-veins was punctured with blood-lancet, and then blood samples were collected by heparinized microhaematocrit tubes; and then after, sealed on one side with cristaseal (Hawksley Ltd., Lancing, UK). The microhaematocrit tubes, about three quarters blood filled, were transferred to a haematocrit centrifuge, and centrifuged for 5 min at 1200 revolutions per minute. After that packed cell volume (PCV) was measured by using haematocrit reader. It was then cut at about 1 mm below the buffy-coat and the contents of the tube expressed onto a micro-scopic slide, mixed and covered with 22 × 22 mm cover slip. Finally, it was examined under 40x and/or 10x objective lens for the presence of motile trypanosomes (Woo, 1969; Murray et al., 1983; Uilenberg 1998); and trypanosome species were identified based on their movement pattern during the buffy coat examination as described by Murray et al. (1977) and Murray et al. (1983).

Entomological studies

Entomological study was conducted from December 2018–January, 2019 and June–August, 2019, which is dry and wet seasons, respectively. A total of 80 odor-baited, acetone and aged cow urine, NGU traps were deployed around the watering and grazing areas closer to trees and bush, which were commonly visited by animals. All the traps were deployed at an altitude of 687 to 1352 masl and at about 200–250m intervals for 48 h. Then after, the flies were collected from the traps and counted, and sex and Glossina species were identified following the standard procedure (Uilenberg, 1998; Pollock, 1982). The flies were sorted into teneral and non-teneral; and then the teneral tsetse flies were subjected to dissection and examination for infection with trypanosome as described by Pollock (1982). Other caught biting flies were identified at genera level according to their morphological characteristics such as size, color, wing venation structure and proboscis (Wall and Shearer, 1997).

Data analysis

Collected data were entered into Microsoft Excel spread sheet, coded and summarized by descriptive statistics. The prevalence of trypanosomosis was calculated as the number of infected cattle divided by the total number of sampled animals and then multiplied by 100 (Thrusfield, 2018). The association between the risk factors and infection of trypanosome were analysed with univariable logistic regression. Those risk factors with p < 0.25 values were further subjected to multivariable analysis. Tsetse flies infection rate was determined as the number of flies having trypanosomes in the gut, proboscis and salivary gland divided by the total number of non-teneral flies multiplied by 100. The apparent tsetse density (AD) was expressed as the number of flies per traps per day (FTD).

Results

Trypanosomosis prevalence

Of the total 964 cattle (i.e. 482 in the dry and 482 in the wet seasons) examined by buffy coat technique 48 (4.98%) animals were found positive for trypanosome infection. The prevalence of trypanosome infection in dry and wet season was shown by Figure 2.

Figure 2

Seasonal prevalence of trypanosomosis.

Univariable and multivariable logistic regression analysis results of potential risk factors considered for the occurrence of trypanosomosis in this study were shown in Table 1. After the risk factors analysis with univariable logistic analysis those variables with p < 0.25 were further subjected to multivariable analysis.

Table 1

Univariable and multivariable logistic regression analysis of potential risk factors trypanosomosis.

Risk factors	Factors level	No examine	No positive (%)	95% CI	Univariable			Multivariable
					OR	95% CI	P-value	OR	95% CI	P-value
Season	Dry	482	15 (3.11)	1.88–5.10	Ref	-	-	Ref	-	-
	Wet	482	33 (6.85)	4.90–9.48	2.29	1.23–4.27	0.009	1.93	1.01–3.71	0.048
Sex	Female	636	29 (4.56)	3.18–6.49	Ref	-	-	-	-	-
	Male	328	19 (5.79)	3.72–8.91	1.29	0.71–2.33	0.405	-	-	-
Age	Young	254	11 (4.33)	2.41–7.66	Ref	-	-	-	-	-
	Adult	710	37 (5.21)	3.80–7.11	1.22	0.61–2.42	0.580	-	-	-
BCS	Good	136	3 (2.21)	0.71–6.65	Ref	-	-	Refe	-	-
	Medium	552	23 (4.17)	2.78–6.20	1.93	0.57–6.52	0.291	1. 93	0.57–6.52	0.217
	Poor	276	22 (7.79)	5.30–11.82	3.84	1.13–13.06	0.031	3.84	1.13–13.06	0.040
Color	White	91	2 (2.20)	0.55–8.44	Ref	-	-	Ref	-	-
	Roan	643	25 (3.89)	2.53–5.48	1.73	0.40–7.43	0.461	1.69	0.39–7.29	0.483
	Gray	173	14 (8.09)	4.84–13.23	3.92	0.87–17.63	0.075	3.68	0.81–16.71	0.091
	Black	32	7 (21.88)	10.66–39.64	12.46	2.43–63.79	0.002	13.18	2.53–68.66	0.002
Total		964	48 (4.98)	3.69–6.55	-	-	-	-	-	-

Trypanosome species identified

Two species of Trypanosomes were identified, which in order of abundance we Trypanosoma congolense (77.1%) and Trypanosoma vivax (20.8%). About 2.1% of the animals were infected by mixed Trypanosome species, T. congolense and T. vivax. Seasonally identified Trypanosoma species were shown in Table 2.

Table 2

Proportion of Trypanosome species identified in dry and wet season (n = 48).

Season	T. congolense (%)	T. vivax (%)	Mixed (%)	Overall (%)	Overall 95% CI
Dry	9 (18.8)	6 (12.5)	-	15 (31.3)	15.6–46.7
Wet	28 (58.3)	4 (8.3)	1 (2.1)	33 (68.7)	49.0–94.9
Total	37 (77.1)	10 (20.1)	1 (2.1)

Hematological findings

The overall mean PCV value of all studied animals was 25.5% (95% CI = 25.2–25.7); and the detail result shown in Table 3.

Table 3

Analysis of the association of trypanosome infections with mean PCV (%) of cattle.

Factors	No examined	Mean PCV	Std. Dev	95% CI	t-test	P-value
Trypanosome
Non-infected	916	25.6	4.18	25.3–25.9
Infected	48	23.0	2.92	22.1–23.8	4.31	0.000
Season
Dry	482	24. 6	4.20	24.2–24.9
Wet	482	26.4	3.93	26.0–26.7	6.86	0.000
Overall	964	25.5	4.16	25.2–25.7

Entomological results

A total of 327 Glossina species and 607 biting flies were caught with 80 NGU traps deployed in the study areas. The overall apparent density of Glossina species and biting flies were 2.04 F/T/D and 3.79 F/T/D, respectively (Table 4). Both in wet and dry season, two species of Glossina were identified, namely: Glossina pallidipes and Glossina fuscjpes. The sex proportion of Glossina pallidipes was 27% male and 73% female, and that of Glossina fuscjpes was 31.8% male and 68.2% female. The biting flies that commonly encountered were Stomoxys species (72.2%) and Tabanus species (27.8%).

Table 4

Summary of the seasonal AD of major fly vectors trapped in the study period.

Season	Traps deployed	Glossina species and F/T/D			Biting flies (AD)
		G. pallidipes	G. fuscipes	Total
Dry	40	56 (1.4)	75 (1.9)	131 (3.3)	14 (0.4)
Wet	40	70 (1.8)	126 (3.2)	196 (4.9)	593 (14.8)
Overall	80	126 (1.6)	201 (2.5)	327 (4.1)	607 (7.6)

AD = Apparent Density.

Glossina species infection by trypanosme

From 327 Glossina species caught 127 fresh and live flies were dissected; and an overall of 15% (19/127) Glossina species was infected by trypanosome. The highest infection rate was found in G. pallidipes 23.5% and the lowest was in G. fuscipes 11.8% (Table 5).

Table 5

Seasonal infection rate of Glossina species by trypanosome.

Glossina species	Dissection and infection rate
	Dry season		Wet season		Overall
	No dissected	No infected (%)	No dissected	No infected (%)	No dissected	No infected (%)
G. pallidipes	16	5 (31.3)	18	3 (16.7)	34	8 (23.5)
G. fuscipes	40	6 (15.0)	53	5 (9.4)	93	11 (11.8)
Total	56	11 (19.6)	71	8 (11.3)	127	19 (15.0)

Discussion

The overall prevalence of trypanosomosis in the study area was 4.98 %. This finding was in a general agreement with the previous reports from the surrounding areas by Teka et al. (2012) and Fayisa et al. (2015) who found 4.43% and 4.86%, respectively. The prevalence of bovine trypanosomosis in southern part of the country was ranging from 1.3% to 29.5% (Girma et al., 2014; Muktar et al., 2016), using the buffy coat methods. The multivariable analysis revealed that significantly higher prevalence was recorded in wet season (p < 0.05, OR = 2.29), poor body condition (p < 0.05, OR = 3.84) and black animals (p < 0.05, OR = 12.46). Though, trypanosomosis is a wasting disease, which result in a progressive condition loss (Steverding, 2008) and poor body condition is not only due to trypanosomosis. Indeed, the body condition of infected animals affected by the level of protein intake. Black coat colour animals more affected by trypanosomosis than the other colour considered in this study as also reported by Sheferaw et al. (2016) and Abebe et al. (2017). As described by Leak (1999) black materials are attracting Glossina species; and this may increase the chance of black coat coloured animals to be bitten by the flies and facilitate the transmission of trypanosoma.

The relatively higher prevalence of T. congolense observed in this study confirms the observation of Gona et al. (2016), Abebe et al. (2017), Tesfaye and Basa (2017) and Eshetu et al. (2017). Various reports (Gona et al., 2016; Abebe et al., 2017; Tesfaye and Basa, 2017; Eshetu et al., 2017) revealed that T. congolense is more prevalent in areas where G. pallidipes is the predominating species.

The overall mean PCV of all the studied animals was 25.5%. The mean PCV (23%) of infected animals, both in wet (23.6%, t = 4.24, P < 0.05) and dry period (21.5%, t = 2.86, P < 0.05), were significantly higher (t = 6.86, P < 0.05) than the non-infected. So, infected animals under any level of diet characterized by drop in PCV (Holmes et al., 2000). But the level of nutrition ans season of infection affect the time of recovery from anaemia, which means rapid in wet season than the dry season (Agyemang et al., 1990). Because nutritional deficiencies reduce PCV (Van den Bossche and Rowlands, 2001). Although, trypanosomosis is characterized by reduced in PCV, it should be known that other factors like parasitism and nutritional deficiencies also causes for lowering PCV.

Two species of Glossina were identified, namely: Glossina pallidipes and Glossina fuscipe. These species were also reported by various authors from areas neighbouring to the study district in a different period (Asha et al., 2008; Sheferaw et al., 2016; Abebe et al., 2017). The total Glossina species caught in wet period was 4.9 Glossina/T/D, which is higher than the dry period 3.3 Glossina/T/D. This is an indication for seasonal variation of Glossina distribution that is relatively higher apparent density observed in wet season (Desta et al., 2013; Majekodunmi et al., 2013; Ouma et al., 2006; Van den Bossche and de Deken, 2002). The decline in the invasion of Glossina species might be due to increasing of mortalities as well as the increasing of the rate of reproductive abnormality during dry season (Torr and Hargrove, 1999). A positive relationship was observed between trypanosome prevalence and the Glossina species apparent density, which implies the higher Glossina species apparent density the higher prevalence of trypanosomosis (Majekodunmi et al., 2013).

From a total of 125 Glossina species dissected 19 (15%) flies were infected by trypanosome species. Overall, higher proportions of G. pallidipes (23.5%) were infected than G. fuscipes (11.8%), which is also true both in dry (i.e. 31.3% for G. pallidipes and 15% for G. fuscipes) and wet (16.7% for G. pallidipes and 9.4% for G. fuscipes) seasons. flies was relatively higher during the dry period; and higher infection percentage was recorded in than in. This finding is in a general agreement with the report of Majekodunmi et al. (2013) and Bitew et al. (2011). According to this author an increasing in the proportion of Glossina infection was followed by increased prevalence of trypanosomosis.

Conclusion

The overall prevalence of trypanosomosis in cattle was 4.98%, and the seasonce prevalences were 3.1% and 6.8% in dry and wet seasons, respectively. Two species of trypanosoma were circulating in the study area, T. congolense and T. vivax, with significantly higher T. congolense distribution. The prevalence of trypanosomosis was significantly higher in wet season, in poor body condition, and black coat animals. Relatively higher Glossina/Trap/Day caught in wet season than dry season. Two species of Glossina namely G. pallidipes and G. fuscipes were distributed in the study areas. The overall proportion of Glossina infection was 15% with higher proportion of infection in wet season than the dry season. Higher infection proportion was observed in G. pallidipes.

Declarations

Author contribution statement

Tadesse Eyasu: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Wrote the paper.

Solomon Mekuria: Conceived and designed the experiments; Contributed reagents, materials, analysis tools or data.

Desie Sheferaw: Conceived and designed the experiments; Analyzed and interpreted the data; Wrote the paper.

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability statement

Data associated with this study has been deposited at Hawassa University website.

Declaration of interests statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.