Detection of Leishmania (Viannia) IN Nyssomyia neivai and Nyssomyia whitmani by multiplex polymerase chain reaction, in Southern Brazil.

Sandflies transmit pathogens of leishmaniasis. The natural infection of sandflies by Leishmania (Viannia) was assessed in municipalities, in the state of Paraná, in Southern Brazil. Sandflies were collected with Falcão and Shannon traps. After dissection in search of flagellates in digestive tubes and identification of the species, female sandflies were submitted to the Multiplex Polymerase Chain Reaction (multiplex PCR) for detection of the fragment of the kDNA of Leishmania (Viannia) and the fragment from the IVS6 cacophony gene region of the phlebotomine insects. The analysis was performed in pools containing seven to 12 guts from females of the same species. A total of 510 female sandflies were analyzed, including nine Migonemyia migonei, 17 Pintomyia fischeri, 216 Nyssomyia neivai, and 268 Nyssomyia whitmani. Although none of the females was found naturally infected by flagellates through dissection, the fragment of DNA from Leishmania (Viannia) was shown by multiplex PCR in one sample of Ny. neivai (0.46%) and three samples of Ny. whitmani (1.12%). It was concluded that Ny. neivai and Ny. whitmani are susceptible to Leishmania infection, and that multiplex PCR can be used in epidemiological studies to detect the natural infection of the sandfly vector, because of its sensitivity, specificity and feasibility.

INTRODUCTION

Knowledge of the fauna composition, behavior, rates of natural infection of the sandfly, Leishmania species identification, and environmental characteristics of endemic areas are essential for the public-health services responsible for protecting populations that live in areas in which leishmaniasis is endemic. Leishmaniasis has worldwide propagation. In Brazil, cutaneous leishmaniasis (CL) has been reported in all states[3].

Cases of CL have increased significantly since the 1980s, and are appearing over wider areas in the State of Paraná, in the South of Brazil[28,29]. This disease has been recorded in occupied areas for more than a century, even in urban areas, contrary to expectations that human pressure would eliminate natural foci and reduce the incidence of this endemic disease[16,33,46]. The organization of rural areas in the Brazilian colonial period created environmental conditions that clearly favor CL transmission[28].

There are several reports of Leishmania detection in sandflies in endemic CL areas in Brazil and in the world[1,32,41]. However, considering the wide geographical distribution of this dermatosis in the Americas[47], knowledge of the natural infection rate of sandflies is still insufficient to estimate the risk of Leishmania infection in many endemic areas.

Given the occurrence of autochthonous CL cases in several municipalities, in the state of Paraná, natural infection rates of sandflies by Leishmania (Viannia) were investigated, in order to identify the species of Leishmania present in locations where cases of this disease had been reported.

MATERIAL AND METHODS

Sandfly collection: Sandflies were collected in the localities of Recanto Marista, Água Azul Farm and Flor de Maio Grange, in the municipalities of Doutor Camargo, Fênix and Mandaguari, respectively, in the state of Paraná, where CL cases had been reported. Sandflies were collected from January through September 2006, from 6 p.m. to 6 a.m., with Falcão light traps and a Shannon trap, installed in woods, domiciles, peridomicile and domestic-animal shelters (cattle shelter and pigsty)[30]. The collected insects were kept alive for further dissection and observation of the natural infection by flagellates.

Dissection and identification of sandflies: The dissection was carried out under a stereoscope; the legs and wings were removed and the dissection was carried out by making two incisions in the distal portion of the abdomen and, with zigzag movements, the digestive tubes were removed and examined under an optical microscope (400 x) in the search for flagellates and the identification of the species of the sandfly[30]. The nomenclature of the species follows GALATI[12].

After dissection and identification[30] of species, digestive tubes were stored at -18 °C in tubes containing 150 µL STE buffer (0.1 M NaCl, 10 mM Tris-base; Na2EDTA-2H2O 1 mM, pH 8.0), each containing seven to 12 guts from females of the same species.

Extraction of DNA: The samples were macerated, and DNA was extracted with a solution of guanidine isothiocyanate and phenol, and hydrated in 20 µL of ultra-pure H2O[31]. For each group of 22 samples submitted for DNA extraction, one negative control (male sandflies) and one positive control [male sandflies plus 104 L. (V.) braziliensis promastigotes] were used.

Multiplex PCR: Two pairs of primers were used: MP3H (5′-GAA CGG GGT TTC TGT ATG C-3′) and MP1L (5′-TAC TCC CCG ACA TGC CTC TG-3′)[18] to amplify a fragment of 70-bp from the mini circle region of the kinetoplast (kDNA) of the Leishmania (Viannia), and 5Llcac (5′-TGG CCG AAC ATA ATG TTA G-3′) and 3Llcac (5′-CCA CGA ACA AGT TCA ACA TC-3′)[17] to amplify a fragment of 220-bp from the IVS6 cacophony gene region of the phlebotomine insects.

The PCR reaction mixture (final volume 25 µL) was composed of 0.5 µM of each of the primers (Invitrogen Life Technologies, São Paulo, Brazil), 0.2 mM dNTP (Invitrogen, Carlsbad, CA, USA), 1U Platinum Taq DNA Polymerase, (Invitrogen, Carlsbad, CA, USA), 1.5 mM MgCl2, 1X enzyme buffer, and 2 µL DNA template. The amplification was carried out in a PC Thermocycler (Biometra, Germany) at 94 °C for seven min to activate the enzyme, followed by 30 cycles, each divided into three stages, of denaturation (1.5 min at 95 °C), annealing (1.5 min at 57 °C), and polymerization (two min at 72 °C). After this, the extension was continued for a further 10 min at 72 °C, and the tubes were then kept at 4 °C until analysis[31]. The amplification products were submitted to electrophoresis in 2% of agarose gel (Invitrogen, Paisley, Scotland, UK) stained with 0.1 µg/mL ethidium bromide, at 10-15 V/cm. The presence of bands was observed in a transilluminator (Macro Vue™ UV-20, Hoefer). For every five samples, one positive control [reaction mixture plus L. (V.) braziliensis DNA] and one negative control (reaction mixture plus water) were added.

RESULTS

In total, 510 (52 pools) female sandflies were analyzed by dissection and multiplex PCR, including nine Migonemyia migonei (one pool), 17 Pintomyia fischeri (two pools), 216 Nyssomyia neivai (22 pools), and 268 Nyssomyia whitmani (27 pools) (Table 1). A total of 244 female sandflies were collected at Recanto Marista, 107 at Água Azul Farm, and 159 at Flor de Maio Grange (Table 1).

Table 1

Sandflies collected in Recanto Marista, Água Azul Farm, and Flor de Maio Grange, in Southern Brazil, from January to September, 2006

Specimens/Localities (Municipalities)		Recanto Marista (Doutor Camargo)	Água Azul Farm (Fênix)	Flor de Maio Grange (Mandaguari)	Total
Migonemyia migonei	Na	9	0	0	9
	Positive pools / Poolsb	0/1	0/0	0/0	0/1
Nyssomyia whitmani	Na	19	97	152	268
	Positive pools / Poolsb	0/2	1/10	2/15	3/27
Nyssomyia neivai	Na	216	0	0	216
	Positive pools / Poolsb	1/22	0/0	0/0	1/22
Pintomyia fischeri	Na	0	10	7	17
	Positive pools / Poolsb	0/0	0/1	0/1	0/2
Total	Na	244	107	159	510
	Positive pools / Poolsb	1/25	1/11	2/16	4/52

Number of Specimens;

Number of positive pools/number of pools composed. Each pool contained seven to 12 guts from females of the same species.

All 52 sandfly pools contained the 220-bp fragment from the IVS6 cacophony gene region of the sandflies, and four pools (7.7%) showed the 70-bp fragment from the mini circle kDNA of Leishmania (Viannia) (Fig. 1). The minimal infection rate of Ny. neivai was 0.46% (1/216), and of Ny. whitmani was 1.12% (3/268). At Recanto Marista one Ny. neivai pool with Leishmania infection was detected on the porch of a domicile; at Água Azul Farm, one Ny. whitmani pool was detected in the peridomicile (near the woods ); and at Flor de Maio Grange, two Ny. whitmani pools were detected, one on the porch of a domicile and another from a domestic-animal shelter. The minimal infection rate of Recanto Marista was 0.41% (1/244), of Flor de Maio Grange was 1.26% (2/159), and at Água Azul Farm was 0.93% (1/107).

Fig 1 -

Multiplex PCR in 2% of agarose gel showing fragments of 70-bp and 220-bp. The fragment of 70-bp of the kDNA mini circle region of subgenus Leishmania (Viannia) were amplified with MP3H and MP1L primers. The fragment of 220-bp of the IVS6 cacophony gene region of the phlebotomine insects were amplified with 5Llcac and 3Llcac primers. Lane 1, Ny. whitmani DNA sample collected in Fênix; lanes 2, 3 and 5, Ny. whitmani DNA samples collected in Mandaguari; lane 4, Ny. neivai DNA sample collected in Doutor Camargo; lane 6, positive control [DNA from L. (V.) braziliensis promastigotes]; lane 7, negative control (all reagents without DNA). M, 100-bp molecular marker (Invitrogen Life Technologies, São Paulo, Brazil).

DISCUSSION

Mi. migonei, Pi. fischeri, Ny. neivai, and Ny. whitmani are frequently found in Brazil[1,2,4,31,34,35,43,46]. Both species detected with Leishmania infection are widely propagated in Brazil[4,5,6,9,20,21] and in the state of Paraná, where either Ny. whitmani or Ny. neivai predominate, depending on environmental characteristics[26,42,43,46].

Although no flagellates were detected in the dissected sandfly digestive tubes, DNA from Leishmania (Viannia) was found in 0.78% (4/510), indicating that at least one infected sandfly was present in each positive pool. The infected specimens were collected at sites near a riparian forest, which is inhabited by small wild mammals (e.g. rodents, armadillo) that are possible natural reservoirs of Leishmania. These locations show favorable environment for the formation of sandfly-breeding sites. Furthermore, the domestic animals are highly attractive blood sources for female sandflies[37,44,45]. Natural infection by Leishmania has been recorded in Pi. fischeri [23,36,38], Mi. migonei [2,7,34], Ny. neivai [8,22,31,41,47], and Ny. whitmani [1,4,11,19], by dissection or PCR, in several localities in many of the Brazilian states.

Natural infection rates of sandflies by Leishmania vary widely: 15.68% in Venezuela by PCR[13], 0.83% and 7.14%[4], and 18.2%[23], in Brazil, by PCR[4], and 1.4% and 2.6%, in Peru, by dissection[15]. Studies on natural infection rates have revealed that PCR is more sensitive and specific than dissection showing the presence of Leishmania in sandflies[10,27,39,40]. This method has often been used in areas where sandfly infection rates are low[27,31], due to its sensitivity (it is able to detect the presence of a single parasite), specificity (independently of the number, location and stage of flagellates in the digestive tubes of the vector)[25,27,34], rapidity, and ease of performance enabling it to be used in leishmaniasis epidemiological surveillance[24]. The dissection of sandflies for the detection of flagellates in the digestive tubes needs confirmation by Leishmania in vitro, cultivation or inoculation in laboratory animals[27] while molecular methods allow the identification of Leishmania species, isolated in cultures from patients or reservoirs, as well from sandflies[25,27].

Several primers have been used[14,27,34], however, the primers used in this study have been tested successfully in diagnosis and detection of naturally infected sandflies, besides having good sensitivity [8 fg/µL of Leishmania (Viannia)][31].

The advantage of employing the multiplex PCR technique is that, in addition to the primers for detection of Leishmania (Viannia), the pair of primers used for internal control can assess the presence of probable interference from digestive contents of insects, which can inhibit the detection of Leishmania [31,34].

The results show the susceptibility of sandflies to Leishmania strains. The minimum infection rates in Ny. neivai (0.46%, 1/216) and Ny. whitmani (1.12%, 3/268) are low, and might explain the low CL endemicity in the municipalities in question. Multiplex PCR, because of its sensitivity, specificity and feasibility, can be used in epidemiological studies to detect the natural infection of the sandfly vector.