Invasive Non-native Species

Pathogens and diseases of wildlife

Pathogens are disease-causing organisms. They come from a large spectrum of species groups, including worms, insects, fungi, protozoa, bacteria, and viruses. Many pathogens are native to Canada and the wildlife diseases they cause are part of the normal functioning of ecosystems. However, some recent disease outbreaks appear to be caused by invasive non-native pathogens or new strains of native pathogens. These include: a bacterium of poultry that also affects house finches; avian influenza, a usually benign virus of ducks that now exists in a strain deadly to poultry; duck plague, a virus native to Eurasia that can kill wild waterfowl; a chytrid fungus of amphibians; and West Nile virus, affecting mammals, birds, reptiles, and people.20

Distribution of birds testing postive for West Nile virus

2001 to 2003
Map: distribution of birds testing positive for West Nile Virus. Click for graphic description (new window).
Source: Leighton, 201020 adapted from Health Canada, 200321

West Nile virus cycles in nature between a wide range of wild bird species and a narrow range of mosquito species. It was transported to North America from Afro-Eurasia.22 First detected in Canada in 2001, it affected all provinces from Nova Scotia to Alberta by 2003, and by 2009, it had reached British Columbia. West Nile virus has killed thousands of corvids (crows, jays, magpies, and their relatives) and fewer non-corvid birds.23

Global spread of chytrid fungus of amphibians

Earliest occurrences of chytrid fungus in each major centre
Timeline: global spread of chytrid fungus of amphibians. Click for graphic description (new window).
Source: adapted from Weldon et al., 200424

A chytrid fungus of the skin has been linked to worldwide declines in amphibian populations25 and is generally believed to be the largest infectious disease threat to biodiversity.26, 27

The origins of chytrid fungus in North America are unclear. It may have originated in Africa and spread through trade of African clawed frogs, which were widely used in human pregnancy tests.24, 26 Trade of other species, such as the American bullfrog, may have contributed to its spread.24 There is some evidence that chytrid fungus has always been present in North America, but that environmental stressors, such as pesticides and climate change, have made amphibians more susceptible to it.28-30 The earliest record of chytrid fungus outside of Africa is from Quebec, in 1961.31Photo: northern leopard frog © iStock.com/maimai

Since then, chytrid fungus has been found in British Columbia,31 Alberta,20 Saskatchewan,32 Ontario, Quebec, New Brunswick, Nova Scotia,31 and, most recently, Prince Edward Island,33 Yukon,34 and the Northwest Territories.35

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