West Nile mosquitoes continue to inundate Williams and McKenzie County traps in greater numbers than usual, and with flood waters only recently receding, the situation is likely to continue.
Hot weather and the extended flood water has made a perfect environment for flourishing Culex tarsalis, Fran Bosch, Williston’s Vector Control Director, explained. As the flood waters recede, they tend to leave behind little pools of water full of organic matter — just what the pregnant female C. tarsalis is looking for.
“The flood stage for the Missouri River is 22 feet,” Bosch said. “We were at 21.96 today. So that is a first. For over two months, it was up as high as 26 feet.”
Above average temperature during spring meant that West Nile mosquitoes also came out of the chute earlier than usual.
“We’ve got a cycle going,” Bosch said. “Next year if we have just a normal flood cycle and it’s up and down in a couple of weeks, we should get back to normal in a couple years. But it won’t happen just like that.”
Two weeks ago, both Williams and McKenzie County had West Nile mosquitoes that tested positive for West Nile virus. This week, West Nile was found in mosquitoes from traps in both Watford City and Grenora.
The Watford City positives were all from Madison Flats, according to Megan Carter, who is in charge of both weeds and vector control For Watford City. She met with Bosch late Tuesday afternoon to plan strategy and schedule an aerial strike against mosquitoes in the Watford City area.
The last report on West Nile had indicated that traps in McKenzie County were positive, but she clarified that those mosquitoes had mainly been down by the river, far away from the city itself. The latest test, however, were for traps on the west side of the city, near Madison Flats, which she described as a large swampy area.
The Air Force is coming back in three weeks to spray again, Bosch said. It will likely be spraying in both McKenzie and Williams County.
West Nile virus does not cause symptoms for most people, but it can lead to serious complications and even death for some.
In 2017, North Dakota Department of Health reported 62 cases of human infection with West Nile virus. Thirty-five percent of the cases resulted in hospitalizations, and two in death.
This year, the state has already reported a human case of West Nile virus in the Ramsey County area. That person was not hospitalized. At about the same time, a pool of mosquitoes in Grand Forks also tested positive for West Nile.
That prompted the North Dakota Health Department to issue a warning urging people to take measures to avoid contracting the virus.
These precautions include:
• Using a repellent such as DEET, picaridin, IR3535, oil of lemon eucalyptus (or PMD), or permetrhin. Apply according to manufacturer instructions;
• Wearing protective clothing, including long-sleeved shirt and pants;
• Limiting outdoor activity between dusk and dawn, when mosquitoes are most likely to bite;
• Eliminating stagnant water in containers around homes, where mosquitoes can lay eggs, such as buckets, flowerpots, old tires, wading pools and birdbaths;
• Keeping grass around your home trimmed.
Old tires, Bosch said, are a favorite hangout for C. tarsalis.
“Any mosquitoes in a tire are undoubtedly going to be Culex,” he added. “Because flood water mosquitoes don’t breed in tires.”
Flood water mosquitoes lay their eggs in soil, Bosch explained. They hatch as flood waters rise and submerge that soil, creating a pool the larvae can swim in. They won’t lay eggs in a tire, and they won’t hatch from soil unless there’s standing water.