Antibodies to avian infectious bronchitis virus in Pakistani chickens.

Using the hemagglutination inhibition test, sera from 20 diseased and 3 apparently healthy chicken flocks in Pakistan were examined for antibodies to four types of avian infectious bronchitis virus (AIBV). These flocks were not vaccinated against AIBV. Of the 900 serum samples from diseased flocks, 78 (8.7%) had antibodies to the Massachusetts (M41) type, 23 (2.6%) to the Arkansas type and 20 (2.2%) to the Connecticut type of AIBV. None had antibodies to the JMK type. None of the sera (n = 100) from apparently healthy layers was positive to any of the four AIBV types tested. Some of the birds with antibody titers exhibited no signs of illness except that they laid pale colored eggs or had a history of poor hatchability. These results indicate that at least three AIBV types are circulating in chicken flocks in Pakistan.