Isolation and pathotyping of Newcastle disease virus isolated from birds in Kerala
U. Rashi, M. Mini, P. M. Priya Surya Sankar and K. Vijayakumar
Newcastle disease (ND) is a pandemic viral disease of poultry. It is highly contagious and causes high morbidity and mortality in affected flocks. The disease is caused by Avian orthoavulavirus 1, commonly known as Newcastle disease virus (NDV) belongs to the family Paramyxoviridae. The virus affects almost 241 species of birds. Based on the pathogenicity, the virus is classified into five pathotypes viz., viscerotropic velogenic, neurotropic velogenic, mesogenic, lentogenic and asymptomatic enteric NDV. The severity of the disease varies with the viral pathotype. Isolation and identification along with pathotyping of the virus provides a basis for understanding the type of virus circulating in the region. In the present study, tissue samples from dead/ ailing birds showing lesions/clinical signs suggestive of ND were collected. They were subjected to virus isolation in embryonated chicken eggs and identified by haemagglutination test and confirmed by haemagglutination inhibition test. Eight NDV isolates were obtained out of 55 tissue samples and were classified into pathotypes by intracerebral pathogenicity index (ICPI) and mean death time (MDT). The ICPI values varied from 0.75 to 1.53 and MDT from 54 h. to 79.2 h. Out of eight isolates, three belonged to velogenic group and five were of mesogenic pathotype. The study revealed the circulation of virulent NDV in Kerala. The pathogenicity tests provide a basis for understanding the epidemiology of ND.
Keywords: Haemagglutination test, intracerebral pathogenicity index, mean death time