Oh, the difference 55 freezes make.
Denton has been trapping and monitoring mosquito pools this year, as it has since a graduate student at the University of North Texas first discovered mosquitoes with West Nile virus in the region in 2002. But so far, none of Denton’s traps have come up positive this year.
The colder-than-normal winter likely killed off mosquitoes that might have survived otherwise. Those surviving mosquitoes can give the virus a jump-start on the season, according to Ken Banks, the city’s director of environmental services.
In addition, the heavy rain in mid-July likely washed away mosquito larvae, Banks said. The city’s storm drains have proven to be a particularly good mosquito habitat.
“When we have a big rain event, even the adults that rest on the [storm drain] walls can get washed away and drown,” he said.
Banks briefed the City Council on the monitoring program last week.
He said July traps showed that the mosquito species Culex quinquefasciatus, sometimes called the southern house mosquito, was increasing, as it often does in midsummer. However, because of the heavy rains, he expects the population to go down when the city gets the next round of reports.
It’s still possible that mosquito traps will test positive for West Nile virus later this summer, he said. If they do, the city will know sooner than it has in past years. A new lab at UNT can test traps and release results in about a day.
The city agreed to help pay for the lab after studying what happened with the virus in 2012. The outbreak was not only the largest the state and city have seen in many years but it also affected far more younger people than in the past.
The city still sends samples to state health officials, however, as part of its monitoring program.
UNT professor Jim Kennedy, who oversees the mosquito monitoring program and who supervised the graduate student who first discovered West Nile in the area, has been following new reports of the chikungunya virus closely.
Similar to West Nile virus, chikungunya virus affects the human central nervous system and can leave lifelong, debilitating effects. The disease is carried by a different variety of mosquito, the Asian tiger mosquito.
But unlike West Nile, trapping and testing for those mosquitoes won’t help as much, Kennedy said.
The West Nile virus grows more prevalent each season through infected birds.
Trapping mosquitoes helps public health officials know when a human outbreak of West Nile is more likely. The chikungunya virus grows only in humans. Once the virus is established in a human population, it will be in the mosquitoes, too, Kennedy said.
There’s another important difference between the two diseases and the mosquitoes that carry them, he said.
Southern house mosquitoes come out at night to bite. But the aggressive Asian tiger comes out during the day.
“They’ll come out of the bushes to bite you,” Kennedy said. “We’ll have to be concerned about mosquitoes both day and night.”
PEGGY HEINKEL-WOLFE can be reached at 940-566-6881 and via Twitter at @phwolfeDRC.