This week Alberta reported its first case of West Nile virus in two years while the United States is experiencing a huge West Nile outbreak with nearly four times the normal number of cases. Officials suspect this is due to the hot summer temperatures and large amounts of rainfall but are also investigating the possibility that the virus has mutated in some way to become more infectious. Of course an outbreak of any kind is often unsettling news. Even though mosquito season is coming to an end, it seems important to discuss a little bit of the biology of the virus in order to aid you in making informed decisions regarding the virus.
The virus was first isolated from Uganda in 1937, it is similar to Dengue virus and Yellow fever virus, and indeed all three of these viruses belong to the Flavivirdiaefamily. Similarly to Dengue and Yellow Fever virus, mosquitoes transmit West Nile virus; however, birds in fact carry the virus. When a mosquito bites an infected bird it harbors the virus inside itself and then, upon biting a human, may transmit the virus. Humans cannot normally pass on the virus from person to person. Exceptions include blood transfusions (this is rare, blood is tested for West Nile virus), and organ transplants (equally rare, the testing of organ donors is rigorous). The virus can be passed through the placental layer to an unborn child and also through breast-feeding. It is important to remember that it is not passed through casual contact.
West Nile virus has a variety of symptoms that appear within 3-14 days of infection. It is important to realize that approximately 80% of those infected will not show symptoms at all and will not experience any form of the disease, their bodies will simply eradicate it. Around 20% of people experience a mild flu-like illness consisting of rash, fever, headaches or body aches. Very few people (1/150) will experience a severe illness which may include high fever, stupor, disorientation, convulsions or even paralysis, coma and death. These effects may last several weeks and may become permanent. However, this is of course very rare. There is no specific treatment for West Nile virus – symptoms are treatable – however there are therapies in the works. For instance, Tom Hobman at our very own University of Alberta has recently discovered how the virus breaks through the blood brain barrier. This research could ultimately lead to antiviral therapies or better treatment options.
Avoiding infection is relatively easy: wear insect repellant, avoid dusk and dawn when mosquitoes are most active and remove standing water basins from backyards. The WHO asserts that the most important aspect of controlling West Nile transmission is controlling the mosquito population.
As with any health reports you read, it is important to know the facts first before taking anyone’s recommendation. Be skeptical and be vigilant when reading any reports and don’t be afraid to ask questions to informed individuals. A great start for information is always the CDC website, and WHO website or the Public Health Agency of Canada.