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| Last Review/Updated: September 1, 2006 |
West Nile Virus (WNv) and wildlife: an Alberta perspective
Frequently Asked Questions
What do I do if I find a dead bird? Although many bird species can be infected with the West Nile virus, mortality is rare except in members of the corvid or crow family (crows, ravens, magpies and jays). Because of these fatal infections and because corvids are widespread across the province, the Alberta West Nile virus wild bird surveillance program focuses on fresh dead corvids, particularly crows and magpies. Bird surveillance will begin June 1, and this year will be limited to the Grassland Natural Region in southeastern portion of the province - the area east of Highway #2 and south of Highway #12. Anyone who finds a fresh dead crow, magpie, raven or jay in this region can drop it off at any Fish and Wildlife office or designated drop-off location. To find the office closest to you, call toll-free 310-0000. Please note that the bird surveillance program for 2005 was completed on September 30. When dealing with any “found dead” wildlife, always wear gloves, use a double plastic bag inverted over your hand, or use a stick to move the dead animal into a container. Do not handle found dead wildlife directly with your hands.
How many dead birds will be tested? The purpose of the bird surveillance program is to determine the presence of the virus in the province. Health professionals and veterinarians will use the information obtained as they assess the risk to humans and horses, respectively. Each natural region has a similar makeup of birds, habitats and weather within that region. Thus, once the virus is confirmed in a region, it is likely that it occurs throughout the region. Based on patterns from previous years, surveillance will be limited to the Grassland Natural Region of southeastern Alberta as conditions in this region are most favourable for development of the Culex tarsalis mosquito. In 2006, the surveillance program will be discontinued once 6 birds have been confirmed positive. What happened with West Nile virus in birds in Alberta last year (2005)? A total of 220 birds was tested for West Nile virus in 2005. The first positive bird was found in mid-August and the number of positives was very low (n=7). All positive birds were from the Grassland Natural Region and included 6 corvids and 1 sage-grouse. For further details, refer to Alberta West Nile virus wild bird surveillance 2005. Birds are the natural habitat for West Nile virus. It is likely that all bird species are susceptible to infection. To date, the virus has been identified in over 225 species of wild and captive bird species in North America. In addition, the virus can occasionally spill over into a few species of mammals and reptiles. The list continues to grow and can be viewed at http://www.nwhc.usgs.gov/research/west_nile/wnvaffected.html. The U.S. National Wildlife Health Center is investigating the possibility that some North American raptor species, including some owl and hawk species common in Alberta, may be more susceptible to West Nile virus than most bird species. To date, there is insufficient information to allow any conclusions about the risk to these species. Infection does not necessarily cause illness and the large majority of infected birds do not show any ill effects of having West Nile virus. Crows and their relatives are the exception. In these species the virus can cause illness and death in many individual birds. There are specific concerns regarding the potential effects of West Nile virus on sage grouse, an endangered species in Alberta. In conjunction with colleagues in the U.S., a group of Alberta wildlife managers, university professors and graduate students is developing possible management responses to try to limit the mortality of sage grouse.
Horses are an exception to the general rule for mammals and they are more susceptible to West Nile virus and closely related viruses. Alberta Agriculture, Food and Rural Development has good information about West Nile in horses, at http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex5455?opendocument. Why didn't "someone" stop the spread of this virus? Like any living organism, West Nile virus is well adapted for its own survival. It can survive in many species of birds and can use a wide range of mosquito species as a means of transferring the virus to new individuals. From its arrival in North America on the east coast in 1999, it quickly spread among local bird populations. Many infected birds were migratory and carried the virus to southern climates where viral transmission continued as these birds intermingled with local mosquitoes and overwintering birds of the same or many different species. During spring migration, the virus was carried northward in a variety of infected birds that spread out across the continent. Thus in 1999, the virus was restricted to the northeast U.S. By the end of 2001, it was in most states east of the Mississippi River as well as in southern Ontario. By the end of 2004, it was found in most provinces and states. This expansion of the West Nile virus distribution reflects the primary bird migration pathways as the virus sequentially entered the Atlantic, Mississippi and Central Flyways. Given the wide range of birds and mosquitoes that the virus can live in, there are virtually endless possibilities for it to survive in North America. This virus is a survivor – it has been around for many years in other parts of the world and will continue to expand its range and distribution when given appropriate opportunities. It is apparent that this virus has already established populations throughout the U.S. and southern Canada. It is also moving south into Mexico, Central America and South America where it will likely establish new populations. Should waterfowl hunters take special precautions? Hunters, like all outdoor recreationists, should take precautions against being bitten by mosquitoes, which are common in wetland habitats and are active at dawn and dusk when temperatures are suitable for insect activity. Health officials advise that there is no evidence or reason to believe that there is any West Nile virus risk from handling hunter-killed birds in Alberta. Free-flying waterfowl are undoubtedly healthy; if not, they would be unable to fly. In addition, the only evidence of direct transfer of West Nile virus from birds to humans without going through a mosquito involve accidental infection when lab technicians were handling many, many heavily infected birds. Do bird feeders pose a risk to birds or to humans? Similar to the comments about handling live birds, bird feeders do not pose a significant concern either for the transmission of West Nile virus nor for the infection of humans. It is recommended that you change the water in bird baths regularly and drain stagnant water in your backyard to reduce mosquito breeding. There have been ongoing problems with salmonella infections at bird feeders
and as a result, feeders and birdbaths should be disinfected regularly
with weak bleach. Since salmonella bacteria can infect humans, anyone
handling potentially contaminated materials should wear gloves and wash
thoroughly when the job is done. See Should bird banders take special precautions? Health officials advise that there is no evidence of West Nile virus risk to persons handling live passerines (perching birds) or waterfowl in Alberta. The majority of birds are not infected and those that are do not contain significant numbers of virus and do not pose a threat to human health. Anyone handling live birds can always increase their protection by wearing gloves. Similar to hunting, bird banding activities often occur at dawn and dusk, thus banders should take precautions to avoid being bitten by mosquitoes. Should bird rehabilitation facilities take special precautions? There are growing concerns that captive or recuperating birds may be at increased risk of West Nile infection. As the virus becomes established in Alberta (as it is likely to do each summer), facility operators would be well advised to screen the facility or take other precautions to avoid exposure of birds to mosquitoes. Preliminary investigation of a vaccine for birds looks somewhat promising, but is not available at this time. Although some facilities have used the horse vaccine on individual birds of critically endangered species, there is no evidence that it provides any protection to birds.
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Mammals
in general are very resistant to infection with West Nile virus. Although
individual wild mammals may be bitten by infected mosquitoes, they generally
produce an immune response that prevents infection. Thus, if we take a
blood sample, we can find antibodies in various mammals but there is no
virus present that could be passed on to mosquitoes. Of course, as with
any infective agent, some individuals may not develop immunity and could
become sick or perhaps even die.