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Subject: Veterinary Pathology × Author: Tamuly, Nibedita × Start date: 2019 ×
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    ThesisItemOpen Access
    Pathomorphological and molecular detection of avian leukosis virus infection in chicken
    (College of Veterinary Science, Assam Agricultural University, Khanapara Campus, 2022-09) Tamuly, Nibedita; Dutta, Biswajit
    Avian Leukosis being a common neoplastic disease of the commercial poultry farm, causes significant economic losses to the farmers. The present study was undertaken to determine the status of the infection in the poultry population from 7 different locations in Kamrup district of Assam. During the period of study, twenty two (22) outbreaks of avian leucosis were recorded from seven (7) different locations of undivided Kamrup district of Assam. A total 243 numbers of post mortem was conducted from which 65 positive cases were reported on the basis of gross examination, histopathological alteration and molecular detection. The overall mortality percentage was recorded as 4.11%. Among different age groups maximum mortality was reported in adult birds above 20 weeks of age (7.36%). However few cases were also reported below 16 weeks of age. Breed/strain wise study revealed highest mortality was reported in BV-380(6.17%) followed by BV-300 (4.47%) which was further followed by Kamrupa (3.49%) and Daothigir (3.47%). Season wise occurrence of the infection was more during winter (4.86%) followed by pre-monsoon (4.11%) and post monsoon (3.68%). Clinically, affected birds did not exhibit any typical clinical signs, however some of the affected birds showed signs like anaemia with pale comb, emaciation with decrease growth rate and productivity and osteopetrosis. The gross pathological study gives a presumptive diagnosis of the diseases where prominent lesions were found in liver, spleen, kidney and heart. In all the cases hepatomegaly was most commonly seen. The affected liver also showed nodular, eucosis or diffuse form of lesions. Spleen, kidney and heart also showed enlargement, necrosis and the presence of nodular growth. Even though the bursal involvement could not be detected due to its rudimentary form in adult birds but in two cases the lesions in bursa was prominent. Microscopic alterations were severe in liver, spleen, kidney, heart and lung characterized diffuse infiltration of immature lymphoid cells, causing distortion of normal parenchyma. Molecular detection by targeting gp85 env gene produced amplification bands at 229 bp. The phylogenetic analysis of the resultant sequences showed 99-100% homology with the endogenous forms of isolates from China, USA and South Korea. Virus can be isolated on 6th day old embryo where replication of the virus was showed by severe hemorrhages and mortality 48-96 hours of post infection. In field condition presence of other neoplastic diseases like Marek’s disease produces similar lesions which complicates proper diagnosis of avian leucosis. In such situations differential diagnosis can be made on the basis of cell cytology, histopathology and Polymerase chain reaction. In histopathology Marek’s diseases affected tissue showed infiltration of pleomorphic cells and on molecular detection positive samples produced bands at 225bp. Myeloid form and erythroid forms were not found during the study. And the present study reveals that infective form of subgroup E of avian leucosis is circulating in the residential poultry population which might undergo mutation along with exogenous forms and create a more severe form of the disease.