West Nile’s peak season set to begin
By Gillian Slade on August 26, 2017.
gslade@medicinehatnews.com @MHNGillianSlade This summer has been relatively free of pesky mosquitoes but we are entering the season of West Nile virus transmitted by bites from certain mosquitoes. There are a number of factors that influence the prevalence of West Nile-carrying mosquitoes including an accumulation of what are called “degree days.” “It is generally assumed that 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 provided by the provincial government. The risk of transmission increases with the increase of Degree Days. “Consistently warmer temperatures will significantly shorten virus development time thereby increasing the potential risk of WNV (West Nile Virus) transmission — should the virus itself be present and other conditions prove to be favourable.” If the temperature is 18 degrees it takes around 30 days for Culex tarsalis (the larvae carrying the virus) to be able to transmit the virus. With temperatures of 30 degrees it takes less than a week, according to government documents about Degree Days published Tuesday. 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. 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. No cases of West Nile have been diagnosed in Alberta so far this year but on a farm near Taber there has been a case of equine West Nile. Saskatchewan has reported its first human case of West Nile and in the U.S. there have been 46 human cases up to July 18 this year. The number of larvae this year in Medicine Hat, collected in samples from bodies of water, has been average, said Scott Richter, superintendent of parks operations. 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. 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. https://open.alberta.ca/dataset/west-nile-virus-and-degree-days-maps-in-alberta-in-2017 http://www.albertahealthservices.ca/info/page14953.aspx 18
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