Swallows and avian influenza: assessing transmission risk to poultry

Working with avian influenza surveillance partners in Ontario, New Brunswick and Nova Scotia in 2022, we collected and tested samples of fecal droppings from over 200 swallows nesting in agricultural landscapes. We did this to determine if swallows may spread avian influenza viruses (AIVs) through their feces in agricultural areas that contain domestic poultry facilities. We found that all samples tested negative for AIVs. Importantly, the number of samples tested was sufficient to detect the presence of AIVs in swallow populations, even at low levels of infection. Although our results show that swallows are unlikely to be main contributors to AIV outbreaks, biosecurity measures preventing contact between wildlife and domestic poultry, including the contamination of feed and water sources, remain the most effective way of preventing AIVs from entering poultry facilities.

Understanding how diseases in livestock spread in agricultural operations is imperative to securing Canada's food supply and ensuring the economic prosperity of producers nationwide. The recent outbreak of highly pathogenic strains of AIVs in Canada proved deadly to domestic poultry, and some wild bird and mammal species. Although wild waterfowl are known as the primary carriers of AIVs during outbreaks — shedding virus through their feces, mucus, or saliva — other wild birds may become infected through close contact or shared environments, such as wetlands. Species of swallows that build nests with mud gathered from wetlands have raised concerns that nests located in, or around agricultural buildings may be to blame for outbreaks on poultry farms. This motivated additional research to understand how this disease spreads between wildlife and domestic animals.

What this means for swallows

Although swallows are not considered primary hosts for AIVs, as wild waterfowl are, we must investigate the potential role of swallows, and other migratory birds, in spreading this disease to domestic animals. Some species of swallows, particularly barn, tree, and cliff swallows, prefer nesting on open structures in agricultural areas, including barns, which house livestock. These findings suggest that swallows are not a primary cause of AIV outbreaks, and the presence of these birds around domestic poultry facilities likely presents a low risk of disease transmission.

This bodes well for the conservation of the barn swallow — a species at risk in Canada that has undergone substantial population declines across North America. Not only do the results indicate that barn swallows may not be susceptible to AIV infection, including often-fatal highly pathogenic AIVs such as H5N1, but they also provide evidence to suggest that farmers do not need to remove barn swallow nests located outside of biosecure domestic poultry facilities.

More work to do

Although this work continues to shed light on which wild bird species serve — or don't serve — as vectors of AIV spread to domestic poultry, we are still working to understand transmission pathways among wild birds through inter-agency disease surveillance programs. The results will provide further insight into how these diseases spread between wild birds and domestic animals, and the steps that producers can take to keep their animals healthy.

Learn more about how these results inform the risk of disease transmission from wild migratory birds to domestic poultry. Take the time to find to get the latest information on the current avian influenza outbreak in Canada at the following Government of Canada webpages:

• Avian influenza in wild birds — Canada.ca
• Avian influenza (bird flu) — Canadian Food Inspection Agency (canada.ca)
• Wildlife and avian influenza — Handling guidelines to protect your health — Canada.ca