No signs of West Nile virus this summer

Duane Hicks

The miserable weather this summer appears to have put a damper on any West Nile virus activity in the Kenora-Rainy River Districts.
Al Mathers, environmental health officer with the Northwestern Health Unit, said they once again have been trapping mosquitoes on a weekly basis in the Fort Frances, Kenora, and Dryden areas, and testing them for the virus, but no positive signs of it have turned up yet.
“We catch mosquitoes, but there’s no virus being detected. There’s just not enough cumulative days of sufficient heat to get the virus moving in the mosquitoes,” noted Mathers.
“It’s been a very, very quiet year.
“It’s been quiet because there’s been no amplification of the virus within the mosquito,” he added, noting that as far as he’s aware, there seems to be a lull in West Nile activity elsewhere in Ontario and the rest of Canada.
Mathers explained that, quite literally, the temperature has to be warmer for a sustained period of time for the virus to circulate in the Culex breed of mosquito which carries it. If there’s no high heat, it just doesn’t occur.
“I think if we had had a hot summer, we would have seen something different across the province. But with the cool, damp summer this year, there just wasn’t enough nice days to get them moving,” he remarked, adding there’s certainly mosquitoes out there biting, “they’re just not carrying the virus.”
Mathers said if the summer had been hotter, he believes testing would have turned up some West Nile-positive mosquitoes in the region.
“I don’t think there would have been that many of them because this is a low-risk area, but I think we would have found a little bit.
“And across the province, I think we would have seen a lot more activity, especially in the southern regions where the Culex mosquito is in larger abundance.”
For sevens years now, health unit staff have used the traps to collect mosquito samples from late June to September. The purpose is to determine what species of mosquito are most common in the two districts.
In past years, only a small percentage of all the samples collected in the region were specimens of the main virus-carrying mosquito species, the Culex (or common house mosquito).
This means the chances of seeing the Culex breed (and thus the virus) here remain slim.
Mosquito season usually tapers off in September, and any mosquitoes spotted in the latter part of that month are not likely looking for a “blood meal” but instead simply are interested in finding a place to go into stasis for the winter.
Mosquito activity normally drops off after nighttime temperatures average 10 C.
Mathers also noted the bird surveillance program, whereby the health unit would accept from the public dead crows and ravens suspected of virus-caused deaths, is not being offered this year, adding it’s no longer provincially-mandated.
If individual health units want to continue with it, they can choose to do so—they just have to pay for it themselves.
“It was only used to detect if the virus is active in an area, and we already know that,” explained Mathers. “The collection was immaterial from that point on.”
In the seven years that the bird surveillance program was conducted, dozens came back from testing with positive results. There also had been very rare cases of the virus showing up in humans and horses.
West Nile virus is spread to humans by the bite of an infected mosquito. Mosquitoes, in turn, become infected by biting an infected bird.
Crows and ravens are particularly susceptible to the virus and thus serve as an effective early-warning indicator.
The virus is not spread by person-to-person contact, and it cannot be spread directly from bird to human, according to the health unit.
The risk of becoming seriously ill as a result of an infection with West Nile virus is low. In fact, most people who become infected experience no symptoms or have a very mild illness, with fever, headache, muscle weakness, or body aches, the health unit reported.
Those at increased risk of severe illness are individuals over age 50 and people with weakened immune systems.
Symptoms of West Nile virus encephalitis (the rare, serious form of the disease) include severe headache, stiff neck, nausea, and vomiting, as well as altered levels of consciousness and mental states.
Tick testing
In related news, the health unit also has been on the lookout for black-legged ticks—and occurrences of Lyme disease—again this summer, but testing has not turned up any reasons to worry.
“We’ve been watching black-legged ticks, or deer ticks, but they only accept now ticks that are found on humans,” Mathers noted. “Before they accepted ticks found on animals, but that’s now changed.
“So, we’ve sent a few through [for testing]. Nothing has been confirmed; we haven’t picked up anything definitive.
“We had one case of Lyme disease, but it was related to a trip to the States. The guy had [the tick] when he was down there,” Mathers added.
The health unit will continue to accept suspicious ticks turned in by the public to determine the presence of deer ticks in its catchment area.
If a tick does bite you and becomes imbedded in your skin, the best bet is using tweezers to remove it, taking care not to remove its mouth, which is key for identifying the species of tick.
If a tick cannot be removed by you, see a doctor to do so.
If it’s a wood tick, they’re fairly easy to identify and are not sent away for testing.
Deer ticks, on the other hand, are smaller than the common wood tick in all three of their life stages (larva, nymph, and adult). They’re three-seven mm in length and dark brown to black in colour, with no white marking on their backs.
Engorged females appear to have an orange/yellow-coloured abdomen.
Adults and nymphs have eight legs; larvae have six.
If there’s a chance it may be a black-legged tick (or deer tick), the health unit sends it to the public health lab in Thunder Bay, then on to Toronto, where it will be identified.
If it’s a black-legged tick, it then is forwarded to the National Microbiology Lab in Winnipeg to be test for Borrelia burgdorferi—the corkscrew-shaped bacterium that causes Lyme disease.
If a specimen sent for testing comes back positive or negative, the health unit will contact the person who submitted it to let them know.
Only about 12 percent of the black-legged ticks actually carry the bacterium.
The Ministry of Health and Long-term Care offers the following advice to foil ticks of any variety:
•Wear light-coloured clothing. It makes ticks easier to spot.
•Wear long pants and a long-sleeved shirt.
•Wear closed footwear and socks, never sandals. Tuck your pants into your socks.
•Use a tick repellent that has DEET. Apply it to your skin and outer clothing (avoid your eyes and mouth).
•Treat your pets and check them for ticks periodically.
•If in an area where you might get a tick bite, it’s important to search your body well for ticks each day.