The course of pigeon circovirus infection in young pigeons experimentally kept under conditions mimicking the One Loft Race rearing system.

Introduction: Racing pigeon competitions are a popular sport where success depends on birds' ability to return fast to their loft of origin. However, many additional factors like differences in feeding, training, everyday care and even geographical loft location influence race outcomes, which has led to the development of the One Loft Race (OLR) system. The OLR system aims to eliminate these factors by housing pigeons from various lofts in equal conditions in one facility. This in turn, however, fosters inter-individual transmission of pathogens.

Material and methods: Fifteen young racing pigeons from five different lofts, naturally infected with pigeon circovirus (PiCV) were reared in one unit for six weeks. Four uninfected birds were kept in a separate unit and were treated as controls for flow cytometry analyses (background establishment). Blood samples were collected every seven days to extract DNA for PiCV quantification using droplet digital PCR and to isolate the mononuclear cells for flow cytometry analyses. On day 42, all birds were euthanised for spleen samples to be collected for further analyses.

Results: The viraemia peak was noted on day 14 of the experiment and subsequently decreased afterwards, with a remarkable decrease noted on day 35. The percentage of IgM⁺ B lymphocytes, including apoptotic cells, in the blood was very similar throughout the experiment. The percentage of apoptotic splenic IgM⁺ B cells was approximately 40% higher in the experimental group than in the control group.

Conclusion: Study results showed that the birds' adaptation period and the specific immunity they had probably developed hindered PiCV replication. Mild PiCV infection led to a slight increase of B lymphocyte apoptosis in the spleen.