West Nile season returns, though numbers have significantly dropped in the past decade

By Gillian Slade on July 12, 2018.

gslade@medicinehatnews.com  @MHNGillianSlade

Alberta Health Services is reminding Albertans to protect themselves against West Nile virus infection.

After being bitten by a mosquito carrying West Nile virus, humans can develop West Nile Non-Neurological Syndrome (formerly known as West Nile fever) or 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.

“With exposure to mosquitoes comes risk of West Nile virus,” says Dr.Vivien Suttorp, medical officer of health in the South Zone. “Because some mosquitoes carry West Nile virus, it’s important to avoid being bitten at all.”

Use an insect repellent that contains DEET, 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 and wear a 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 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 2016 when there were five cases, three of which were in the south of the province. Of the seven cases reported in 2017, one was the neurological type and the other six non-neurological.

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