Hot temperatures can mean higher risk of West Nile

By Gillian Slade on August 15, 2018.

Sustained hot temperatures result in an increased threat of mosquitoes that can transmit the West Nile virus.

gslade@medicinehatnews.com @MHNGillianSlade

Sustained hot temperatures result in an increased threat of mosquitoes that can transmit the West Nile virus.

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.

By the end of July there had already been six cases of West Nile confirmed in Canada. Five of those were in Ontario and one in Manitoba. There are no cases yet confirmed in Alberta, according to Alberta Health online data.

West Nile 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 320 in 2007.

The numbers dropped dramatically after that with only one in 2008, two in 2009, and nine 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, three of which were in the south of the province, according to data provided on Alberta Health’s website.

In 2017, there were seven cases in Alberta, with four in the south zone, two in Calgary and one in central Alberta.

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://www.canada.ca/en/public-health/services/diseases/west-nile-virus/surveillance-west-nile-virus/west-nile-virus-weekly-surveillance-monitoring.html