West Nile Virus and the Environment

Much attention has been paid to the human health implications of West Nile virus, but it is important to consider the environmental implications of this disease.

West Nile virus presents a number of environmental challenges, including the effects of the disease on wildlife health and populations, particularly migratory birds, and the impacts of mosquito control and management strategies.

West Nile virus has been confirmed in nearly 200 species of birds in North America, striking down waterfowl, shorebirds and landbirds alike. Nearly 200 owls, including the lone remaining birds of several northern species, died during an outbreak at the Owl Foundation in Ontario. Several Loggerhead Shrikes, an endangered species in Canada, have also died from the disease. While many experts believe that most bird populations will eventually develop an immunity to the disease, some species may simply not have the numbers to withstand the threat.

West Nile virus also has the potential to indirectly impact birds, other wildlife, their habitats and aquatic life through efforts taken to control mosquito populations.

A variety of pesticides are used in Canada for mosquito control, ranging from reduced risk biological-based products to more traditional chemical products. The Pest Management Regulatory Agency regulates the use of pesticides in Canada.

One mosquito control option is the use of biologicial larvacides, a naturally occurring bacteria that when commercially formulated, kills mosquito larvae. Bacillus thuringiensis israelensis (BTi) is the only microbial larvacide registered for use in Canada. Studies show that BTi has minimal impact to both human health, and the environment. This larvicide is now available to the general public for use in large bodies of standing water on private properties, but care needs to be taken to apply the product carefully and judiciously, especially if the standing waters may flow off site to sensitive aquatic habitat.

Decisions on whether or not to use stronger pesticides to control the spread of West Nile virus in communities are made by local and provincial governments. The Government of Canada provides guidance to provinces and municipalities to help them make informed decisions on control measures for their jurisdictions. If insecticides are implemented, only products registered under the Pest Control Products Act for mosquito control can be used, and mosquito control programs must be undertaken in such a way that they will minimize risk to Canadians or the environment.

However, there is little empirical data available that measures the long-term effect of mosquito control programs on the environment.

Environment Canada, in collaboration with the Pest Management Regulatory Agency, is working on the Government of Canada Position on the Use of Pest Control Products to Control Potential Vectors of West Nile Virus to help provinces, territories and municipalities make informed decisions on control measures for their jurisdictions.