By Gillian Slade
Southern Alberta Newspapers – Medicine Hat
This summer has been relatively free of pesky mosquitoes, but we are entering the season of West Nile virus transmitted by bites from 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.
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.
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.
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.