Are passerine birds reservoirs for influenza A viruses?

Abstract Although peridomestic passerine species have been involved in influenza A virus (IAV) outbreaks in poultry, there is little evidence to indicate they serve as reservoirs for these viruses under natural conditions. Recent molecular-based detections of IAV in terrestrial wild birds have challenged this paradigm, and it has been suggested that additional research is warranted to better define the role of these birds as IAV hosts. To address this need, we reviewed the published literature reporting results from IAV surveillance of passerines. We also conducted prospective virologic and serologic surveillance of North American passerines for IAVs. The literature review included 60 publications from 1975-2013 that reported results from 829 species of passerines and other terrestrial birds. In our prospective study during 2010 and 2011, 3,868 serum samples and 900 swab samples were collected and tested from 102 terrestrial wild bird species from Georgia, New Jersey, Delaware, and Minnesota, USA. Antibodies to the nucleoprotein of IAV were detected with a commercial blocking enzyme-linked immunosorbent assay in 4/3,868 serum samples (0.1%); all positive samples were from Minnesota. No virus was detected in 900 swab samples by virus isolation in embryonated chicken eggs or matrix real-time reverse transcriptase PCR. Our results are consistent with historic literature; although passerines and terrestrial wild birds may have a limited role in the epidemiology of IAV when associated with infected domestic poultry or other aberrant hosts, there is no evidence supporting their involvement as natural reservoirs for IAV.