A serological survey for avian infectious bronchitis virus and Newcastle disease virus antibodies in backyard (free-range) village chickens in Mexico

The commercial flocks in Yucatan, Mexico are free of Newcastle disease viru s (NDV) in its velogenic viscerotropic form, but little is known about the disease status of backyard poultry. A seroprevalence survey in 30 villages using haemagglutination inhibition (HI) tests for infectious bronchitis vir us (IBV) and NDV antibodies was carried out from December 1997 to June 1998 . The seroprevalences were 56.5% (95% CI 50-63%) for IBV and 2.2% (95% CI 0 .5-3.8%) for NDV. All the villages had chickens that were positive for anti bodies to IBV and nine of the villages had chickens that were positive for antibodies to NDV. This suggests that IBV may be responsible for a large pr oportion of the respiratory disease observed in backyard chickens in Yucata n. The implications of these findings are discussed, including the highly s usceptible status of the backyard chickens in Yucatan to NDV and the possib ility of this virus being one cause of the syndrome known as mortandad by t he local people.