Manitoba health officials are reporting the first case of human West Nile virus (WNV) in the province this year in a female in her 50s from the Southern Health–Santé Sud region.

West Nile virus
Culex quinquefasciatus

The patient did not experience neurological symptoms and was not hospitalized.  She is believed to have been exposed during the week of July 26.

Prior to this case, Canada has seen four WNV cases–2 in Ontario and 2 in Quebec in 2015, according to surveillance data.

In Manitoba, the main carrier of the virus is the Culex tarsalis mosquito. The department’s surveillance program found this season’s first Culex tarsalis mosquito samples infected with WNV during the week of July 12.

Last year, Canada saw 21 human WNV cases, with five in Manitoba [Interlake-Eastern Health Region (1), Prairie Mountain Health Region (2), Southern Health Region (1) and Winnipeg Health Region (1)].

WNV is spread by the bite of an infected mosquito. Mosquitoes are WNV carriers that become infected when they feed on infected birds. Infected mosquitoes can thenspread WNV to humans and other animals when they bite. Rarely, WNV also has spread through transfusions, transplants, and mother-to-child.

Related: West Nile virus season is upon us, how bad could it get?

Approximately 80 percent of people who are infected with WNV will not show any symptoms at all. Up to 20 percent of the people who become infected will display mild symptoms, which appear 3-14 days after getting infected, and include fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms typically last a few days.

About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, andneurological effects may be permanent. There is no specific treatment for WNV infection. Prevention is by avoiding mosquito bites and eliminating mosquito breeding sites.

Robert Herriman is a microbiologist and the Editor-in-Chief of Outbreak News Today and the Executive Editor of The Global Dispatch

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