Transmission Dynamics of Visceral Leishmaniasis in Nepal

Abstract

Visceral leishmaniasis (VL) is also well-known as kala-zar is one of the neglected tropical disease, caused by a protozoan parasite, Leishmania speices and transmitted to humans by the bite of infected female P. argentipes sandflies. Humans are assumed to be the only established reservoir of VL including Nepal, India and Bangladesh.In human, VL may be either symptomatic or remain asymptomatic. So, it becomes necessary to know the role of symptomatic and subclinical infections in transmission of VL. Therefore, the main objective of this study was to elucidate the transmission of VL in Morang, Saptari, Sarlahi (confirmed endemic districts with VL control program) and Palpa (recently confirmed as endemic to VL) districts of Nepal. For this study, 331human blood samples, 3976 sandflies samples from 142 HHs and 100 domestic animals (cow, goats, dog, buffaloes and ox) blood samples were collected from 2016 to 2019 from the villages of the four districts. Using the rK39 rapid immunochromatographic strip test, the human blood samples, were tested for anti- Leishmania antibodies. And from genomic DNA extracted from human blood, female P. argentipes sandfly and animal blood samples, amplification of kDNA of L. donovani was done PCR amplification. 32 and 16 out of 331 people screened were rK39 test positives and by PCR respectively. Among the 16 PCR test positives in human blood sample, 10 were from Sarlahi, 2 from Saptari, 1 from Palpa and 3 were from Morang districts. Among these 16 PCR positives, 10 were VL symptomatic and 6 were asymptomatic cases of VL. This study also showed that the sandfly species P. argentipes is the most predominat species. Most of the sandfly collected harbor Leishmania parasites. We did not found Leishmania infection in domestic animals blood samples. The existence of VL cases, detection of Leishmania DNA and anti-rK39 antibodies in human blood samples showed that there is continuing transmission of VL in Morang, Palpa, Sarlahi and Saptari districts. However the maximum transmission was detected in Ishworpur village, Sarlahi district. This study reveals domestic animals were not the reservoir for L. donovani in tested villages. Thus, humans can be consider as reservoir host for L. donovani in Nepal. Thus, continuous investigation is essential to identify transmission in the new foci and previous endemic districts.