The threat of West Nile virus is prompting the province to take action against mosquitoes in Portage la Prairie.
The province hopes to begin fogging the city with malathion as early as today, Manitoba Health medical officer Dr. Richard Rusk said on Wednesday afternoon, noting Portage la Prairie has a high concentration of mosquitoes carrying the West Nile virus.
The province does not plan to make additional interventions in Winnipeg. "Here in the city, those (mosquito) levels have not come up to a level where there's enough risk," Rusk said.
So far this year, 48 mosquito samples taken from 17 Manitoba communities have tested positive for West Nile.
Temperature and wind conditions could push the fogging to a different day. But once it begins, Rusk said, the province will keep a close eye on mosquito density around Portage la Prairie and continue fogging until the pests' numbers drop to a more comfortable level.
Two Manitobans have been found to have West Nile in 2012; they are the first to be confirmed infected since 2009. One patient was not aware he was infected. The other had been sick with mild flu symptoms, but did not know the virus was to blame.
Both of those patients were from Winnipeg and discovered they had West Nile when they were screened by Canadian Blood Services.
That kind of case history is common -- the majority of people infected with the virus may never know anything is amiss -- but serious infections can strike even healthy people. Seven people have died of West Nile in Manitoba since 2002.
The decision to fog Portage la Prairie was based on a complex mathematical model, Rusk said. It takes into account the number and density of Culex tarsalis mosquitoes, how many tested positive for West Nile and human population density where the mosquitoes are found.
Rusk said the province is mindful of what happened in 2007, which saw 587 confirmed cases of West Nile among Manitobans, a sudden spike in numbers that dropped quickly the next year.
"The reality with West Nile is it can infect more very quickly," he said. "In 2007, at the beginning of the season, we had very few actual cases... By the end of August, it was the highest number we've ever had."
The province is tracking its data on West Nile online (at www.gov.mb.ca/health/wnv). Manitobans are advised to take steps to reduce mosquito populations -- such as cleaning eavestroughs and reducing standing water around their homes -- and protect themselves against bites with mosquito repellent or loose, light-coloured clothing.