The epidemiology of Newcastle disease (ND) was studied in free-range chickens in Bangladesh . The study population was followed for 9½ months by interviews, post-mortem examinations (including tissue samples for virus isolation and characterisation) and blood serum collection. Approximately 90% of the village families reared chickens of which only 11% regularly vaccinated their chickens against ND. Another 14% of the chicken rearers occasionally vaccinated their chickens and 75% did not vaccinate at all. Mortality due to ND was higher in unvaccinated flocks compared to the vaccinated flocks, i.e., 21.6% and 4.9% respectively. The mortality was significantly higher in unvaccinated growers compared to chicks and adult birds. There was no significant difference between mortality due to ND in vaccinated or unvaccinated male and female birds. ND outbreaks were more frequent in unvaccinated flocks during November to January (winter) compared to August - October = Autumn (dry season). From 8 out of 24 samples it was possible to isolate ND virus (NDV), and 2 isolates were characterized as velogenic NDV. The first serological profile of unvaccinated flocks showed that 75% of the adult birds had NDV antibodies, 7.3% of the growers and 3.3% of the chicks had NDV antibodies. In the vaccinated flocks the serological profile showed that 96.15% of the adult birds, 80.26% of the growers and 55.10% of the chicks. There was a significant difference in antibody level between unvaccinated and vaccinated flocks during the study period. Furthermore, there was a highly significant difference in the NDV antibody level between the different age groups for neither unvaccinated and vaccinated birds.

The efficacies of a locally produced F-strain of Baby Chick Ranikhet Disease Vaccine (BCRDV), an M-strain of the Ranikhet Disease Vaccine (RDV), and a commercially produced vaccine ND-clone 30 (live lentogenic La Sota) were compared. two groups of chickens were vaccinated and 1 group served as control. Group 1 was vaccinated with BCRDV intraocularly at day 3 and day 28 followed by RDV intramuscularly at day 60. Group 2 was vaccinated with ND-clone 30 intraocularly at day 3, day 28, and day 60. On day 75 the groups were challenged with a velogenic field strain. Blood samples were collected for serum at day 3, day 28, day 60, and day 74 from all groups. Serum titre was highly significant in Group 1, compared to group 2 after using RDV, and protection was good when challenged with field velogenic virus after titration. There was significant difference in clinically affected birds between groups 1 and 2. No significant difference was found between groups 1 and 2 in relation to dead birds after challenge infection, even though there was 10 % mortality in Group 2.

Related Projects