ABSTRACT
Newcastle disease is one of the most important diseases of poultry. It usually causes a great loss in poultry industry and domestic village chickens. Since domestic chickens in villages are free ranging for food, the chance of their contact with wild birds that may act as reservoirs is high. To determine the role of domestic chickens in the epizootiology of Newcastle disease virus in villages of Isfahan province, 400 serum samples from chickens with no history of vaccination from four regions [Khomeinishahr, Zarinshahr, Falavarjan and Mobarekeh] were collected in summers of [1998] and [1999]. Haemagglutination inhibition [HI] test was used for titration of antibodies against Newcastle disease virus. Chi-square and binomial tests were used for statistical analyses. 69.5 and 68.5% of the sera were positive in the two consecutive seasons [P>0.05]. About 25% of 3-4 month- and 1-2-year-old chickens were negative for HI antibodies and thus were sensitive to the disease in each season. Significant correlation was observed between the HI antibody liters and the age of the chickens [P<0.01]. A specific pattern of seroconversion was observed which was independent to the prevalence of the disease in industrial poultry flocks in each region and all regions studied. It was concluded that about 35% of the domestic village chickens are protected against virulent strains of Newcastle disease in summer. For protection of the remaining chickens, routine vaccination, especially in spring and summer is suggested