Outbreak of Viscerotropic Velogenic form of Newcastle dis-ease in vaccinated six weeks old pullets

An outbreak of very virulent form of Newcastle disease in 6 week old pullets is reported. The flock was vac-cinated against Newcastle disease with Newcastle disease vaccine intra ocular at the hatchery and Newcastle disease vaccine Lasota at 4weeks of age at the farm. The signs noticed by the farm Manager were yellowish and greenish watery faeces, weakness and decrease in feed consumption. Response to treatment with Bioxin® (oxy tetracycline) was poor. The sick birds never recovered. The gross lesions observed were: Necrosis of the gastrointestinal tract (Payers patches), caecal tonsils and bursa of fabricius. The disease lasted for 11 days and the mortality rate was 99.7%. The high mortality rate suggested that the vaccine had failed to immunize the birds against Newcastle disease and the birds were highly susceptible and had been infected with a very pathogenic stain of Newcastle disease virus.