Ontario remains the Canadian hot zone for West Nile virus
This 2006 photo made available by the Centers for Disease Control and Prevention shows a female Aedes aegypti mosquito acquiring a blood meal from a human host at the Centers for Disease Control in Atlanta. (The Canadian Press/AP - Centers for Disease Control and Prevention - James Gathany)
Published Wednesday, September 5, 2012 7:15PM EDT
TORONTO -- Ontario remains the hot zone for West Nile virus activity in Canada this summer, with a case count that climbed 41 per cent over the past week.
Public Health Ontario, the province's public health agency, says in its weekly West Nile report that there have been 116 confirmed and probable cases in the province.
Manitoba has the next most cases, with 20, Quebec has recorded 19 and Saskatchewan and Alberta have had three cases apiece.
There have been no West Nile-related deaths in Canada this season.
Meanwhile, cases continue to mount in the United States, which is having its worst West Nile virus year to date on record.
The U.S. Centers for Disease Control say there have been 1,993 cases and 87 deaths in 48 states; Texas has recorded the lion's share of the cases, 1,013 as of Wednesday.
By the time it was issued, the CDC count was already out of date. It was compiled with numbers collected at the start of the work day Tuesday. But by Wednesday, Texas was reporting another five deaths, which would take the national toll to 92.
In Canada, the issue of out-of-date numbers is also a problem. The Ontario report, based on cases reported as of Sept. 4, lists 57 confirmed and probable cases for Toronto.
But Toronto Public Health's website now says there have been 61 confirmed and probable cases in the city. Toronto has had the largest number of cases this year in Ontario by far.
A spokesperson for Toronto Public Health says about one third of the people in the city who've been diagnosed with West Nile virus needed hospital care.
Of the 20, six remain in hospital, Kris Scheuer says. Four of those people are in intensive care units.
Other Ontario hot spots include Windsor-Essex and Halton counties. Other counties in the southern part of the province have had a smattering of cases.
Canadian Blood Services is currently using enhanced screening procedures in Hamilton, London, Ont., and Winnipeg because they've recently detected donations that were positive for West Nile virus at blood clinics in those centres, a spokesperson for the agency said Wednesday.
Ron Vezina, director of communications for the blood agency, said donated blood is typically tested for West Nile virus in pooled lots, with six donations per lot. That approach saves time.
West Nile virus can be transmitted via blood transfusion.
If a positive result comes back, each of the units in the pool is individually tested and only the infected unit is discarded. When the positive unit is found, the location of the donor is identified.
Then the agency moves to enhanced testing, screening each unit from that area individually. If no new infected units are found within seven days, pooled testing is resumed.
This year has definitely been a more active West Nile year than the previous few, Vezina said.
So far in 2012, 15 infected units of blood have been identified and pulled from the system. Last year, six infected units were found. In 2009 and 2010, no infected blood was discovered.
While it won't be clear for several weeks, West Nile activity may have already hit its peak in several areas. It takes some time for people bitten by infected mosquitoes to become ill, seek medical help if they need it, get tested and receive a test result.
Officials in Texas said Wednesday that August is typically the worst month for infection there, so the accumulation of new cases could start to slow down soon.
In Canada, Manitoba Health says that the most recent surveillance information on the type of mosquitoes most associated with spread there -- Culex tarsalis -- suggests the numbers are decreasing throughout southern Manitoba.