There have been no cases of humans being infected with the West Nile virus in the Sun Country Health Region ... so far.
Dr. Shauna Hudson, chief medical officer for the region, said there has been only one individual in the province testing positive for the virus and he showed no symptoms. The only way the infection was detected was due to the fact the man was attempting to donate blood when the virus showed up in the pre-draw test.
Hudson said culex tarsalis mosquitoes, the type that carry the West Nile virus, have been identified in the local health region though. She said two were caught in a trap about one week ago. The traps have been set in Sun Country for the past 11 weeks and this was the first reporting of the culex tarsalis type.
"They have been trapped in very low numbers since. We've never had more than 100 culex tarsalis in any trap and usually it's well below 100 which is lower than previous years and especially lower than 2010. Last year, the count was very low around Estevan and Weyburn where we had two positive tests on West Nile in mid-August around Estevan. There was one positive test in Weyburn."
"This year it was Week 32 when we got our first positive find of this mosquito and it was Week 32 last year and Week 30 in 2010 and it was Week 25 in 2007 which was the biggest year for culex tarsalis," said Hudson.
"It seems they are now showing up later in the season and we're usually getting 10 culex tarsalis mosquitoes in traps overnight and some are infected with West Nile but there hasn't been a lot of transferring to birds or horses yet," said Hudson.
But with persistent hot weather, the mosquitoes are still around so the population is not at zero risk, at least not for a little while.
Those engaged in harvesting operations are warned that the mosquitoes thrive in the rural areas. Culex tarsalis are small mosquitoes that like to bite the lower body.
That means the usual warnings and precautions are to be observed such as wearing long sleeved, light coloured clothing, especially if you have to be out at dawn or dusk, using insect repellent with DEET, cleaning out eaves troughs, old tires and bird baths and any other place where there is a possibility that water can collect and remain stagnant.
Philip Curry, provincial entomologist for the Health Ministry, said there have been no signs of any strict pattern of arrival or departure of the culex tarsalis other than it appears to be coming in a bit later in recent years.
Last year's floods actually helped eradicate a large volume of mosquitoes, he said. Yes, there was a lot of standing water after the event, but the flooding actually wiped out a lot of traditional mosquito breeding territory, he said.
"Larvicide programs, especially in the cities, have also helped keep the numbers down," said Hudson and Curry.
The entomologist noted though that even with over 10 years of careful scrutiny and study, there is still no human immunity to West Nile, although there has been some in birds, that are usually the first species to be infected, followed by horses and humans.
"In 2003 and 2007 we had very high activity with a big buildup of mosquitoes the year before, then the years following those, the situation was not as bad," said Curry.
Weather, of course, was a big factor although 2003 was a dry year, the infestation was high due to the build up a year earlier. Mosquito larva can easily survive over winter.
"The southeast had a higher activity level in previous years. Anyone born after 2007 wouldn't have any natural immunity and after 2003 we had cold and wet conditions in the spring that worked against the culex tarsalis."
Curry added that the work he and his staff do continues to concentrate on tracking the high mosquito counts that carry West Nile, knowing that there will always be culex tarsalis mosquitoes around so the problem will never be eradicated.
"Hot weather in summer means more people are out enjoying the weather, which, in turn, means more possibility of exposure to mosquitoes," he said.
"We need immunity to block it, but we're not near that yet. A lot of people have never been exposed and you can't assume that just because you've had mosquito bites, you're immune," Curry said.
This summer's early rains and high winds helped keep the mosquito count down too.
"We've done evaluation of larvicide programs and they are effective especially in hot, dry years when the mosquitoes' natural habitats are reduced. Programs in the cities are more effective and West Nile sites can be identified and treated. The larger the city, the better the chance of reducing mosquito counts. For instance the City of Regina has a larvicide program in all sectors within the city and for 10 kilometres outside the city limits. Mosquitoes can fly three kilometres a night, so let's say with 27 square kilometres being treated, you have a good combat system," Curry said.
"Culex tarsalis is a rural mosquito, it likes the shallow ponds, just like you have in the Souris Valley, so you have the challenge right there, but control programs like the larvicide program you have, does work. But for the farm community, there's just too much habitat, so I would suggest to the farmers to focus on their own farm yards and regional parks and eliminate the breeding areas there. Clean up the septic systems, get rid of old tires, water livestock away from the dugout or slough and keep the water fresh, put screens on your doors and remember the life cycle for a typical mosquito is just four weeks ... but then the next generation comes along," Curry said in conclusion.
