Epidemiological investigations on the role of clinically healthy racing pigeons as a reservoir for avian paramyxovirus-1 and avian influenza virus

Abstract

Clinically healthy racing pigeons may harbour notifiable pathogens and serve as an unnoticed reservoir. Thus, 3480 healthy racing pigeons from 172 different lofts were monitored over a period of 2 years for the presence of avian influenza virus (AIV) and avian paramyxovirus-1 (APMV-1). Pharyngeal and cloacal swabs as well as blood samples were collected from juvenile and adult pigeons. Pools of five pharyngeal swabs per loft and age group were initially screened by real-time reverse transcriptase-polymerase chain reaction (rRT-PCR). Pharyngeal and cloacal samples from lofts that were positive or suspect in the AIV rRT-PCR or the APMV-1 rRT-PCR were inoculated into embryonated chicken eggs for virus isolation. In addition, sera were examined for antibodies against AIV by enzyme-linked immunosorbent assay. The antibody levels after vaccination against APMV-1 were determined by haemagglutination inhibition assay. Of the investigated lofts, 0.0 to 1.4% were positive by rRT-PCR for APMV-1 and 0.0 to 6.7% for AIV during this 2-year period with a total of four samplings. No sample yielded replicating virus in egg culture. No antibodies against AIV were detected. Haemagglutination inhibition test of vaccinated racing pigeons indicated age-dependent APMV-1 titres. The results suggest that the examined racing pigeons may have had contact with AIV, but virus replication may have been too low to induce detectable circulating antibody levels. Only a low percentage of samples were positive for APMV-1, but two outbreaks were observed in monitored flocks, indicating ongoing circulation of APMV-1 in the racing pigeon population. These observations highlight the relevance of APMV-1 vaccination and indicate the importance of flock immunity.