ABSTRACT
Seventeen infectious bronchitis virus (IBV) field isolates recovered from commercial broiler flocks in Mexico were identified by reverse transcription-polymerase chain reaction cycle sequencing of the S1 gene. The isolates were obtained from broilers on farms from the neighboring states of Queretaro and San Luis Potosi in 1998 and 1999. Flocks had an ongoing history of bacterial-complicated respiratory disease with mortality rates as high as 28% in spite of receiving live vaccinations for Massachusetts and Connecticut strains of IBV. Sequence analysis of the S1 gene identified two unique genotypes that have been described, as of this time, only in Mexico and thus appear to represent strains indigenous to the country. The Mex/1765/99 genotype was isolated from 64% (11/17) of the respiratory disease outbreaks. Three isolates (18%) were similar to the BL-56 genotype, a unique Mexican IBV strain observed initially in 1996. In addition to the two indigenous strains, three isolates (18%) were found to be the Connecticut genotype.