Following the recent announcement of a human case of West Nile virus in Alberta, the perils of this mosquito-borne virus are once again making headline news.
Though the probability of becoming ill from West Nile infection is low, news reports suggest the public should be afraid--very afraid. With an abundance of mixed messages and sensationalized media coverage, it can be difficult to determine the reality of the threat.
West Nile is a mosquito-borne virus that can cause West Nile Fever or, in serious cases, West Nile Neurological Syndrome. There is evidence of West Nile in Alberta, particularly in the Southeastern region of the province. If infected, a person may experience headaches, fever, nausea, chills, body aches, muscle weakness, numbness, or even paralysis. In the most severe instances, West Nile can cause death.
'"West Nile is a 'low risk, high consequence' disease," said Deputy Provincial Health Officer Dr. Karen Grimsrud. "Twenty per cent of those infected will get West Nile fever, but people can get quite ill. It is not as benign as you might think."
The Government of Alberta is taking precautions with their 2005 West Nile Response Program, which is modified based on the response plans of previous summers, as well as information from other jurisdictions. It focuses on raising public awareness about the disease, and through a surveillance program that tests for the virus in mosquitoes, animals, and humans. Funds are also distributed to municipal larval control programs in areas at highest risk for West Nile virus.
Still, the key messages about West Nile are unchanged.
"The most effective way to prevent infection is through personal protective measures--wearing repellant with DEET, covering up with long sleeves and trousers, and avoiding outdoor activities at dawn and dusk whenever possible," said Grimsrud. Citizens are also encouraged to eliminate any standing water that may have collected around their homes and yards where mosquitoes lay their eggs.
Calgary Varsity MLA Harry Chase believes these measures are insufficient to protect Albertans. He is particularly concerned with the assessment of high risk areas, which were determined using 2003 surveillance data.
"They are using statistics from a dry summer." said Chase. "Calgary and Edmonton have received extraordinary amounts of rainfall. We can't isolate the risk to only the Southeast portion of the province. They are basing their reaction on statistics from a dry summer and are not funding based on this summer's moisture level."
However, Grimsrud disagrees, noting the Culex tarsalis breeds best in dry climates.
"These mosquitoes like dry, hot weather," said Grimsrud. "They are within the expected range. They don't do well in wet weather."
The question of whether the 2003 data is still appropriate is a valid one. There is no specific treatment for West Nile, and much is still unknown about the virus and activities of its host.
This lack of information is prompting Chase to call for preventative measures to be taken while the insect is in the larval stage.
"It is extremely debilitating for those who contract it," he said. "If this province would take a more pro-active, preventative approach, we could be improving the health of Albertans."
"The risk of acquiring West Nile virus is related to exposure--time spent outdoors in high risk areas," said Provincial Labratory for Public Health Clinical Virologist Dr. Kevin Fonseca.
West Nile is nearly always contracted through mosquito bites. While it can be transmitted through blood or organ transfusion, the screening process makes this almost impossible.
"The viraemic period in humans is relatively short--maybe a few days," explained Fonseca. "Humans are dead-end hosts."
This means personal protective measures will remain the most effective way to prevent West Nile infections.