West Nile Virus is back in Ontario, but hasn’t yet raised its ugly head in Renfrew County.

The Ontario Ministry of Health and Long Term Care issued a notice last week that the number of mosquitoes with the virus is on the rise across the province, especially in Southern Ontario.

Eighty-nine positive mosquito pools have been found in the province to date, mostly in the Windsor and Golden Horseshoe areas, which is the highest for the same time period since 2002.

WNV-carrying mosquitoes have been detected in the Kingston and Ottawa areas as well.

The province is also seeing probable and confirmed human cases of West Nile virus appearing, which typically start to occur in August and September.

Bob Schreader, manager of environmental health with the Renfrew County and District Health Unit, said that rise in virus numbers is due to the hot weather, which has been encouraging its spread. He noted WNV tends to come in cycles, with peak years fading off into ones where the occurrences are much lower.

So far in Renfrew County there has been no sign of the virus in local mosquitoes.

“We’ve been continuing our mosquito monitoring program here for the past six weeks, and WNV hasn’t been seen in any of the population pools,” he said.

Mr. Schreader believes there are two main reasons for this; first, the dry weather has greatly reduced the number of mosquitoes in urban areas – one of their traps only caught six mosquitoes within a local municipality during the week of July 15-21, while in comparison, that same week in a rural area, the trap was filled with 1,028 mosquitoes.

The other factor seems to be in the species of mosquito prevalent in the county. Mr. Schreader said local varieties are not efficient WNV carriers.

Schreader said they have been monitoring the mosquito populations across the county for a decade now, and it appears the local varieties aren’t prolific at carrying WNV.

“Most of the mosquitoes we are collecting are ones which are a very weak vector for West Nile Virus,” he said. “This is not to say it isn’t out there, just to say the main thing going for us is we don’t have the species of mosquito which normally carries it.”

West Nile Virus is a mosquito-borne virus that can very rarely cause encephalitis (inflammation of the brain). The virus was named after the West Nile region of Uganda, where it first appeared in 1937.

West Nile Virus is spread to humans through the bite of a mosquito which has become infected with the virus. Mosquitoes get the virus by feeding on infected birds. It is not transmitted from person to person, or directly from a bird infected by West Nile Virus to a person.

Less than one per cent of people who acquire West Nile Virus develop severe symptoms from the disease, and less than one per cent of them who contract it become seriously ill from the West Nile Virus. Most people only exhibit mild, flu-like symptoms, if they get infected at all.

The risk of becoming seriously ill with West Nile Virus is very low and most people who become infected experience no symptoms or have very mild illness. Despite that, the virus had become the subject of a provincial monitoring program since the late 1990s, with the first traces of the virus being detected in dead birds found in Renfrew County in 2002. However, the virus has never was detected in local mosquito populations.

Several years ago, the county ended an ongoing dead bird collecting program, but have maintained mosquito trapping to monitor the virus.

Mr. Schreader said their trapping program is set to wrap up by the Labour Day weekend.

Even though the risk is low for WNV, the health unit continues to advise people to take precautions by reducing mosquito breeding areas on their properties by eliminating sources of standing water. This includes recycling/disposing of unwanted containers, draining water regularly from flower pots, window boxes, planters and swimming pool covers, making sure eaves troughs are clean and drain properly, changing the water in bird baths at least once per week, removing and recycling old tires, plastic containers and paint cans, and turning over wheelbarrows, canoes and plastic wading pools to drain standing water.

The health unit also states it is always wise for residents spending time outside in mosquito territory to wear light coloured clothing, including long sleeves, pants and hat, to cover exposed skin, use insect repellent containing DEET on exposed skin, and ensure all windows and doors to your home have screens that are in good condition.

Stephen Uhler is a Daily Observer multimedia journalist

stephen.uhler@sunmedia.ca