High death rate from West Nile led to mosquito trapping in Reno County last year

Health officials are continuing to use properties in southern Reno County this summer as one of just three mosquito trapping regions for tracking West Nile Virus in the state.

Reno County became a trapping site in 2017, after three people living within the Turon area zip code died from West Nile complications between 2013 and 2016, said Ingrid Garrison, state public health veterinarian with the Kansas Department of Health and Environment.

Extremely high mosquito counts – more 10 times numbers that normally trigger action – were discovered in some of the first traps set in the region, leading to a concerted response by health experts which included going door-to-door in Turon to advise residents about action and prevention steps.

So far this year, mosquito counts have been high a couple of times, but well below the numbers from 2017 and there have been no pools found with the West Nile Virus.

Still, with heavy rains in recent weeks followed by high temperatures that result in quick breeding, numbers have spiked, so local health officials advise residents to remain cautious and take measures to protect against mosquito bites.

The process

A federal grant from the Centers for Disease Control and Prevention is funding the placement of more than a dozen traps in three Kansas counties, and assessing the mosquito counts from the traps to develop an early warning system for disease, Garrison said.

Initially, CDC funding in 2013 concentrated traps in Sedgwick County as “a sentinel county” for the state for West Nile contamination.

Then in 2017, the CDC added more funding to also test for the Zika virus. That allowed the state to expand trapping and testing to Reno and Shawnee counties.

“For 2018, we plan to continue with five traps (in Reno County),” Garrison said. “Reno County Health Department staff are placing them in predetermined locations around the county.”

The traps are put out one evening a week at several locations in primarily western Reno County, then collected the next morning.

Mosquitoes, which are most active at dusk and dawn, are drawn to the traps by a small light and carbon dioxide gas given off by dry ice stored in a black-coated can at the top of the trap. The gas escapes through small holes circling the bottom rim of the can.

A tiny, battery-powered fan draws the insects into a white mesh bag, which they are then unable to escape.

When staff pick up the traps the next day, the mosquitoes are gently brushed or blown to the bottom of the net, placed in a brown paper sack and then placed on dry ice, which causes the insects to go dormant.

Once the traps are back at the health department, they are poured onto a “chill table,” and the mosquitoes quickly swept into test tubes for shipping to the state lab in Topeka.

Working in a small area that used to be a closet at the Reno County Health Department, environmental staff race to get the mosquitoes bottled before they thaw and fly off.

As long as the mosquitoes are kept cold, any virus they are carrying will not degrade, Garrison said.

Dangerous species

At the lab, Dr. Christopher Rogers of the Kansas Biological Survey views the mosquitoes under a microscope to sort them into their species and count them.

That’s because different species carry different diseases and a couple, in particular, are of interest to Kansas scientists.

The Aedes albopictus and the Ae. Aegypti mosquitoes, two non-native, invasive species known to carry the Zika virus, have been detected in Kansas, though not widespread, and no Zika virus has been found in mosquitoes the state.

The others species watched for is the female Culex spp., which transmits West Nile.

The captured mosquitos are ground up and their DNA tested for diseases.

A report is prepared and sent back to Reno County and other health officials in western Kansas weekly.

Dozens of times over last summer, mosquitoes in the Reno County traps tested positive for West Nile, Garrison said.

“Frequently all the traps were positive,” she said. “Reno County had far and away the most positive counts (in the state), but we didn’t really know why.”

Officials recommend spraying for adult mosquitoes when populations exceed 40 mosquitoes or more per trap.

Two of the first traps set near Turon in Reno County last year captured more than 600 mosquitoes each.

“It was an anomaly,” Garrison said. “We usually don’t see that many in June either.”

In other parts of the county, counts were much lower.

“Six-hundred is quite a bit,” she said. “We needed to do something.”

The response

The state assisted the City of Turon in implementing mosquito fogging twice a week and went door-to-door handing out larvacide “dunks.”

“We couldn’t be more proud of the response from Turon,” said Reno County Health Department Director Nick Baldetti. “Their reception was very welcoming.”

Officials recommend using larvacide in standing water if a trap count exceeds 20 mosquitoes.

“Larvacide lasts 30 days in a treated area,” Garrison said. “They’re very effective. It’s the most efficient treatment source when mosquitoes are breeding.”

The larvacide pellets, also known as bricks, are non-toxic except to specific species of mosquito larvae, Garrison said. They are not harmful to fish or other aquatic life.

Besides bringing mosquito counts down dramatically, there were no recorded cases of West Nile infection in people in Turon, Reno County or neighboring Stafford County in 2017.

“For 2018 the surveillance plan is the same,” Garrison said. “We’ll continue weekly trapping and testing of mosquitoes with the Kansas Biological Survey. The Reno County Health Department’s assistance is crucial in setting the traps and talking to landowners (who have to permit placing traps on their land.)”

Beyond counting

The testing is not only important for Reno County, but for health department across much of the state, since Reno County is a “proxy” for four of the six reporting regions in the state.

The other testing sites are Sedgwick County, for Southeast Kansas, and Shawnee County, for the northeast sixth of the state.

Besides counting and testing mosquitoes, the scientists are exploring environmental conditions to look for explanations why Reno County had such high West Nile counts. Data they are collecting includes rainfall amounts, temperatures and prevailing winds.

“North of Turon this is a large cattle stockyard,” Rogers noted. “But the prevailing winds go in the wrong direction. We’re at a loss right now. We have to do more focused data collection to figure out what is actually happening.”

One thing hampering their study is access to property, since they need the permission of landowners to go anywhere.

“We grew up on a farm, so I’m not going to go on a farm without permission,” Rogers said.

Closer into town, they haven’t seen as much standing water in ditches or fields as in the southwest portion of the county, Rogers said, though there tend to be more containers that hold small amounts of standing water.

Soils may also play a role, since sandier soils, besides draining more quickly, tend to draw more predatory insects because of their chemical makeup, Rogers said.

With the CDC funding, the state last year also surveyed some 637 municipalities and all 105 counties in the state to see what kind of mosquito controls are used.

“Half the cities and 20 percent of the counties had performed no mosquito surveillance, which is important for directing mosquito controls,” Garrison said.

Particularly since mosquitoes in some areas have developed resistance to commonly used pesticides.

“It’s not just an issue in Kansas,” Garrison said. “The National Association of City and County Health Officials did a study a year ago and found the overwhelming majority of vector controls are in need of improvement.”

The agency mapped the level of each state’s capability for surveillance and control – and ranked Kansas as a 0, or virtually no control.

Federal funding for future testing, however, is uncertain beyond this year, the health officials advised.

One way to reduce the number of mosquito-borne illnesses is to prevent mosquitoes from breeding and laying their eggs in standing water. Mosquito dunks, which are designed to kill mosquito larvae, are made from harmless bacteria that is animal and pet-friendly.

If you have standing water on your property and cannot drain it – such as fish ponds, rainwater in ditches, bird baths, stock tanks or ponds – pick up some free dunks at the Reno County Health Department, 209 W. Second. They are available first-come, first-serve until they run out. Staff can also provide information on their proper use.