FILARIAL PARASITES IN LIVESTOCK WITH SPECIAL REFERENCE TO Onchocerca armillata
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Date
2017-07
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College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati-781022
Abstract
A study was conducted to record the prevalence of filarial nematodes in cattle, buffalo and goat in Kamrup district of Assam (Metro and Rural) in local abattoirs in and around Guwahati from January 2016 to January 2017. A total of 792 animals comprising cattle (n=430), buffalo (n=262) and goat (n=100) was examined for this study. In cattle 3 species of adult filarial parasite (Setaria labiato-papillosa, S. digitata and O. armillata) and in buffaloes 2 species (S. labiato-papillosa, S. digitata) of adult filarial parasite could be recorded. Light microscopic morphological studies of these parasites were conducted. Based on the presence of lesion, Stephanofilaria assamensis could be encountered in 16.00% cattle. Setaria species infection was 62.50% in buffaloes. Prevalence of Onchocerca armillata in cattle was 68.40%, more in female Jersey cross bred animals (83.09%). Skin nip examination of cattle revealed presence of O. armillata microfilariae in 28.57% cases of O. armillata infection-positive cases. The molecular identification of ITS1-5.8S rDNA gene of Onchocerca isolate of the present study revealed 95% similarity with O. fasciata which complemented the light microscopic identity of the parasite. The molecular identification of 16S rDNA gene of Wolbachia revealed 99% similarity with O. volvulus, O. ochengi, O. cervicalis and O. gutturosa. Studies on the pathology of O. armillata infected aortae could reveal three major lesion types viz., parasitic migratory tracts in the intimal layer, nodular lesions in both intimal and adventitial layer and umbilical cord-like lesions in the intimal layer. These three lesion types appeared in the aortae either as a single or in combinations. Generally there was mild infiltration of inflammatory cells particularly mononuclear cells admixed with polymorphs and a few giant cells with thickening and edema of intimal layer. Migratory tracts showed empty spaces lined by fibrous connective tissue and proliferation of collagen fibers. Nodular lesions consisted of necrotic parasites and microfilariae inside them and inflammatory cell infiltration predominated by eosinophils. Umbilical cord like lesions exhibited edematous and massive fibrotic areas with calcification. In the present attempt, developmental stages of larvae and pupae of Simulium metatarsale and S. bhutanensis were encountered at 12 different breeding sites, with predominance of the former species. Presence of Wolbachia in Simulium metatarsale could be detected through a molecular identification of Wolbachia specific 16S rDNA gene. The results revealed 99% similarity with Wolbachia of other species obtained from different geographical regions. The Wolbachia obtained from S. metatarsale had 100% similarity with Wolbachia of O. armillata of the present isolate.