Isolation and characterization of Newcastle disease virus from vaccinated commercial layer chicken

Abstract

Aim: Newcastle disease (ND) is an infectious, highly contagious and destructive viral disease of poultry and controlled by vaccination. In spite of vaccination, incidence of ND was reported in commercial layers with gastrointestinal lesions. This study was undertaken to assess the prevalence and pathotypes of Newcastle disease virus (NDV) involved in gastrointestinal tract abnormalities of vaccinated commercial layer chicken of Namakkal region for a period of three years from 2008 and 2011.

Materials and Methods: Pooled tissue (trachea, lung, spleen, proventriculus, intestine and caecal tonsils) samples collected from dead birds on postmortem examination from 100 layer flocks above 20 weeks of age with gastrointestinal lesions were subjected to isolation of NDV in embryonated specific pathogen free (SPF) chicken eggs. Mean death time (MDT) and intracerebral pathogenicity index of the isolates were characterized. Flock details were collected from NDV positive flocks to assess the prevalence and impact of NDV on vaccinated commercial layer chicken.

Results: Among the 100 flocks examined Newcastle disease virus was detected in 14 flocks as a single infection and 10 flocks as combined infections with worm infestation, necrotic enteritis and coccidiosis. Chicken embryo mean death time (MDT) and intracerebral pathogenicity index (ICPI) values ranged from 50.4 to 96.0 hrs and from 0.650 to 1.675 respectively. Affected birds showed anorexia, diarrohea and drop in egg production. Macropathologically, matting of vent feathers, petechial haemorrhage on the tip of proventricular papilla, caecal tonsils and degeneration of ovarian follicles were noticed. The incidence of ND was most commonly noticed in 20-50 wk of age and between the months of September to November. Morbidity rate varied from 5% to 10% in the NDV alone affected flocks and 5 to 15% in NDV with other concurrent infections. Egg production drop from the expected level ranged between 3 to 7 % in ND and 5 to 10 % in concurrent infections. Average mortality in NDV and concurrently affected (NDV and Coccidiosis) flocks were 2.89% and 3.50 % respectively.

Conclusion: The present study revealed 24 % of gastrointestinal tract abnormalities in commercial layer chicken were caused by various pathotypes of Newcastle disease virus. The virus caused the disease as single and concurrently with other diseases. Vaccination minimized the clinical manifestation and lesions even in velogenic virus affected flocks.