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West Nile Virus

Background

West Nile Virus (WNV) is a Flavivirus that can infect and cause disease in people, birds, horses, and many other animals.


WNV was found to occur in North America (New York, USA) for the first time in the summer of 1999. Prior to this the virus found in Africa, Asia, and Europe. WNV has now spread and is endemic to virtually all jurisdictions in North America, except for the far North and British Columbia.


WNV is transmitted by the bites of infected mosquitoes (at least 50 species worldwide). It is susceptible to sunlight and drying and thus does not survive long in the environment or on the skin of a person who washes with soap and water.


WNV multiplies in the tissues of infected birds, circulates in the blood, and may be picked up by mosquitoes taking blood meals from these birds. These infected mosquitoes may then transmit the virus when they fly to another bird or animal and feed again. Most birds do not become ill when infected with this virus, but individual birds of over 135 species (as of March 2003) are known to have become ill after infection.


Crow-family birds (including crows, ravens, magpies, blue jays, gray jays and steller's jays) are very susceptible to the WNV and often die when they are infected, due to inflammation of many organs including the brain (encephalitis) caused by the virus. For this reason, crow-family birds have been chosen as an indicator species for the presence of WNV.


Although wild birds are the usual host animals infected by WNV, the virus also may infect amphibians, domestic poultry, domestic mammals (particularly horses), humans, apes, and monkeys.


West Nile Virus may cause mild disease in people, resulting in fever, frontal headache, muscle aches, swollen lymph nodes and skin rash. Less commonly, it causes severe disease that is marked by headache, fever, neck stiffness, muscle weakness, stupor, disorientation, coma, and death. The disease is usually more severe in the elderly or in those already suffering a serious illness. The incubation period (interval between infection and the onset of disease) in people is usually 5 to 15 days. Please visit the Public Health Agency of Canada website for human disease information.


There is no WNV vaccine available for use in humans. For those people that have fallen ill from WNV infection, supportive care has shown to aid in recovery.


A vaccine has been approved for use in horses and can be acquired through veterinarians. Some bird rehabilitation centers' and zoos have used this horse vaccine. The effectiveness of this practice is not known.


People are best off taking personal protective measures against WNV. This can be done by avoiding times of day with high mosquito activity such as dawn and dusk, by avoiding known infected areas, by draining any standing water around your home, by refreshing the water in your bird bath at least twice a week, by using screens on windows and doors, by wearing long clothing and by using an effective mosquito repellent. Visit this website for more information about mosquitoes.


Click here to view an article with more information on West Nile Virus.