Although the isolation and identification of CAV as well as other recent diagnosis of the virus in broiler flocks have provided evidence for chicken anemia virus, Brentano & Ottati (1999), the prevalence of CAV had not yet been determined in Brazil. Since the knowledge of the prevalence of the virus and the level of antibodies against CAV in breeders flocks provide key information for designing control measures against chicken infectious anemia, we conducted a serological survey in broiler breeders of different ages, in five States with intensive commercial broiler flock production. Of a total of 2,355 sera tested by a commercial ELISA assay, 89% were found positive for antibodies to CAV, indicating a high prevalence of the virus in Brazil, in all the surveyed states. The analysis of antibodies to CAV in 6 to 70 week-old breeders showed that flocks between 6 and 18 weeks of age have the highest number of seronegative and low antibody titer chickens, thus representing the age group with the most uneven level of immunity against CAV. Chickens with negative or low antibody titers were still detected until 24 weeks of age, whereas at 25 weeks there was a 100% seroconversion to CAV and a reduction to less than 2,5% in the number of chickens with low antibody titers. These results provide evidence for a gradual and progressive virus spread in broiler breeder flocks, with the occurrence of a small percentage of chickens with low antibody titers at beginning of lay and therefore susceptible to inadequate transfer of passive immunity and vertical transmission of CAV to their progeny.
chicken anemia virus
