Passive immunity to West Nile virus provides limited protection in a common passerine species.

Passerine birds have played an important role in the establishment, maintenance, and spread of West Nile virus (WNV) in North America, and some are susceptible to WNV-associated mortality. Characterization of passive transfer of anti-WNV antibodies in passerines is important to understanding transmission and demographic effects of WNV on wild birds. We showed passively acquired maternal antibodies to WNV in the house sparrow (Passer domesticus). Although all seropositive females (N = 18) produced antibody-positive egg yolks, only 20% of seropositive mothers (3/15) produced seropositive chicks. The estimated average half-life of maternal antibodies in chick sera was 3 days, and no antibodies were detected after 9 days post-hatch (DPH). Maternal antibodies failed to provide protection against viremia in chicks at 21-25 DPH. Although the observed duration of persistence of passively inherited anti-WNV antibodies in house sparrows differs from some non-passerine birds, it remains unknown whether similar patterns occur in other passerines.