Evaluating the role of wild songbirds or rodents in spreading avian influenza virus across an agricultural landscape

Abstract

BackgroundAvian influenza virus (AIV) infections occur naturally in wild bird populations and can cross the wildlife-domestic animal interface, often with devastating impacts on commercial poultry. Migratory waterfowl and shorebirds are natural AIV reservoirs and can carry the virus along migratory pathways, often without exhibiting clinical signs. However, these species rarely inhabit poultry farms, so transmission into domestic birds likely occurs through other means. In many cases, human activities are thought to spread the virus into domestic populations. Consequently, biosecurity measures have been implemented to limit human-facilitated outbreaks. The 2015 avian influenza outbreak in the United States, which occurred among poultry operations with strict biosecurity controls, suggests that alternative routes of virus infiltration may exist, including bridge hosts: wild animals that transfer virus from areas of high waterfowl and shorebird densities.MethodsHere, we examined small, wild birds (songbirds, woodpeckers, etc.) and mammals in Iowa, one of the regions hit hardest by the 2015 avian influenza epizootic, to determine whether these animals carry AIV. To assess whether influenza A virus was present in other species in Iowa during our sampling period, we also present results from surveillance of waterfowl by the Iowa Department of Natural Resources and Unites Stated Department of Agriculture.ResultsCapturing animals at wetlands and near poultry facilities, we swabbed 449 individuals, internally and externally, for the presence of influenza A virus and no samples tested positive by qPCR. Similarly, serology from 402 animals showed no antibodies against influenza A. Although several species were captured at both wetland and poultry sites, the overall community structure of wild species differed significantly between these types of sites. In contrast, 83 out of 527 sampled waterfowl tested positive for influenza A via qPCR.DiscussionThese results suggest that even though influenza A viruses were present on the Iowa landscape at the time of our sampling, small, wild birds and rodents were unlikely to be frequent bridge hosts.

Utilising citizen science data to rapidly assess potential wild bridging hosts and reservoirs of infection: avian influenza outbreaks in Great Britain

“…Furthermore, while passerines tend to show low test positivity rates for HPAI infection (Wade et al 2023, EFSA 2022) and may therefore have limited capacity as biological sources of virus (i.e., virus replicates inside the wild host), they may also play a role as mechanical transporters via fomite (e.g., virus carried externally on feet or feathers). External swabbing of small passerines in the United States during previous outbreaks found no support for mechanical transport potential via fomites (Houston et al 2017). However, small sample sizes together with large populations typical of small passerines lead to low confidence in prevalence.…”

Highly pathogenic avian influenza A(H5N1) in animals: A systematic review and meta-analysis

“…These birds can carry the virus without showing signs of illness. Some birds may develop immunity after exposure to the virus, which can limit its spread within bird populations [ 71 , 72 ]. Influenza viruses, including H5N1, can undergo genetic changes through mutation and reassortment.…”

Avian Influenza A Virus Associations in Wild, Terrestrial Mammals: A Review of Potential Synanthropic Vectors to Poultry Facilities

“…mouse was assessed to be antibody positive by ELISA but was negative by HI tests [88]. A third study evaluated small mammals associated with Iowa poultry farms, some of which were located in counties that had HP IAV activity during 2015, several months after the 2015 outbreak had ceased [89]. None of the samples (a relatively small number of external and internal swabs) tested positive by PCR, nor did any of the subset of blood samples collected from small mammals (house mice, Peromyscus sp., meadow voles [Microtus pennsylvanicus], Norway rats, northern short-tailed shrews [Blarina brevicauda]) test positive for IAV antibodies [89].…”