No new cases of West Nile virus were reported this past week in Oklahoma, according to state Health Department data.
Oklahoma has seen 176 cases of West Nile virus and 12 deaths this year, the highest number of reported cases and deaths the state has seen since the virus entered the U.S. in 1999.
West Nile virus is spread through the bite of the Culex mosquito, which feeds on infected birds and then transmits the virus by biting humans, horses and some other mammals, according to the state Health Department.
Most people who contract the virus show little or no symptoms. People older than 50 are at most risk of developing serious symptoms related to West Nile virus, including paralysis and brain swelling.
State Epidemiologist Kristy Bradley said even though there's been a dramatic decline in the number of cases, the mosquito population is not gone.
A hard freeze or multiple freezes does not kill off the mosquito population. Rather, over the winter, the mosquito population goes into diapause, a dormant state similar to hibernation, she said.
“The Culex mosquitoes are actually quite capable of overwintering and can sustain and remain viable through low freezing temperatures as long as they find protected areas,” Bradley said. “That might be cracks and crevices, or getting into homes, getting into barns, getting into other outbuildings to overwinter where they can be protected from the drying, really harsh winds.”
At this point in the year, most mosquitoes have stopped seeking blood meals or at least slowed down their efforts in biting humans and other mammals for food, Bradley said. Mosquitoes seek out blood meals to get the energy to lay eggs. Right now, they're stopped or slowing reproduction efforts.
Mosquitoes are triggered out of diapause in the spring when the days get longer. Those that survive the winter will become more active in the spring and resume their biting and seeking blood meals, Bradley said.
“It's the diapause that works in our favor because they're less interested in biting people and more interested in finding a nice warm comfy place to ride out the winter,” she said.