Molecular characterization of velogenic viscerotropic Ranikhet (Newcastle) disease virus from different outbreaks in desi chickens

AIM: Diagnosis of velogenic viscerotropic Ranikhet disease from six different flocks of desi chicken in and around Mumbai by gross and histopathological examination, isolation of virus and molecular methods. MATERIALS AND METHODS: A total of 25 carcasses (varying between 2 and 6 carcasses from each flock) of six different flocks of adult desi chicken were subjected to necropsy examination for diagnosis of the disease during the span of a year (2014-2015). After thorough gross examination, the tissue samples were collected and processed for virus isolation and histopathological examination. The 20% tissue homogenate was inoculated into 9-day-old specific pathogen free (SPF) embryonated eggs. Mean death time (MDT) of embryos after inoculation and intracerebral pathogenicity index (ICPI) were used to judge velogenic nature of the virus. Newcastle disease virus (NDV) was isolated from six cases and confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) targeting the partial fusion protein gene of the viral genome. RESULTS: spp. in three flocks was also noted. In this study, viscerotropic velogenic form of ND was confirmed in all six outbreaks by gross and microscopic examination, virus isolation and RT-PCR. CONCLUSIONS: In this study, viscerotropic velogenic form of ND was confirmed in all six outbreaks by gross and microscopic examination, virus isolation and RT-PCR. Nowadays, vaccine strains Lasota, B1 and F strains are used widely in India to control the infection of NDV. However, virulent NDV strains are still isolated frequently in the birds under backyard and also in commercial venture which demonstrates that NDV remains an on-going threat to commercial as well as backyard poultry flocks.