Three cases of West Nile diagnosed in Alberta
Three cases of West Nile virus have been confirmed in the province.
One was in Calgary and two in the Alberta Health Services’ south zone which, includes Medicine Hat.
There are a number of factors that influence the prevalence of West Nile-carrying mosquitoes, including an accumulation of what are called “degree days.” A total of 109 Degree Days above 14.3 C are required for 50 per cent of mosquitoes to be able to transmit the virus, according to online details. The risk of transmission increases with the increase of Degree Days.
If the temperature is 18 C it takes around 30 days for Culex tarsalis (the larvae carrying the virus) to be able to transmit the virus. With temperatures of 30 C it takes less than a week, according to government documents.
In the past, West Nile season activity has started once the 150-200 Degree Day threshold is met in the southeast of the province.
According to a provincial map showing Degree Days, effective Aug. 20, a swath of land covering Saskatoon and Calgary has 350-400 degree days while this region sits at the 250-300 mark.
West Nile virus can cause West Nile Non-neurological Syndrome or, on rare occasions the more serious West Nile Neurological Syndrome.
Those with West Nile Non-Neurological Syndrome may experience fever, chills, nausea, vomiting, fatigue, skin rash, swollen glands and headache. People who develop West Nile Neurological Syndrome may experience tremors, drowsiness, confusion, swallowing problems, high fever, unconsciousness, paralysis and even death.
In 2003, there were 275 cases of West Nile in Alberta and in 2007 there were 320. The numbers dropped drastically after that with only one in 2008, two in 2009, nine cases in 2012 including a local man who died that October from West Nile Neurological Syndrome. There were 21 cases in 2013 and then nothing until last year when there were five cases, three of which were in the south of the province, according to data provided on Alberta Health’s website.
It is not possible to tell which mosquitoes near you are carrying West Nile virus, so it’s best to avoid being bitten at all, says Alberta Health Services. Use an insect repellent that contains DEET and limit your time outdoors at dawn and dusk when mosquitoes are most active. Cover up with long-sleeved shirts and long pants in light colours.