What’s the county’s role in fighting mosquito-borne diseases?

​When reports come out on increased chances of contracting West Nile Virus, or some other nasty mosquito-borne disease, a lot of people want to know what Collin County's role is in the fight to check its spread.

Here's a brief run-down of what our folks do in our jurisdiction, the unincorporated areas of the county. Our cities all have their own measures and plans in place, which you can check out here.


During mosquito season, which runs from May to November, the county's Development Services staff is on watch for signs that arbovirus activity is on the rise. A bit more than half of Collin County's 886 square miles is unincorporated, rural land that has to be monitored for disease-carrying mosquitoes.

Once a week, some 10 remote sites are checked with two kinds of traps each to capture and test live mosquitos known to carry West Nile Virus or worse, the Zika virus.

Tuesday mornings, traps are set out, and Wednesday mornings they're checked for some pretty dangerous characters who go by the name of Culex Quinquefasciatus or Aedes Albopictus. True, mosquito trapping is a lot less dramatic than that, but the results of week-in, week-out checking are important when it comes to getting ahead of an outbreak of West Nile Virus.

The next week, traps are set out at a different set of locations. A couple traps are kept on hand in the event a breakout of human cases are identified, or Development Services gets a report of increased mosquito activity.

The only postponement for the checks comes when rains and high winds make these checks futile, since species like the Culex need about two weeks of dry, calm weather to successfully breed and hatch offspring.

Captured suspects are quickly shipped live to a lab in Austin and checked for West Nile virus, and a host of other nasty conditions that are classed together and called arboviruses. Results come back a few days later, and should the laboratory isolate a virus, the lab sends word back to the county and other state health offices about what's been detected.

Back in Collin County, a positive West Nile Virus mosquito pool prompts the staff to map out and identify residences and businesses within a half-mile radius of the pool, the outer limits of the flight path of the mosquito. Neighbors get a notice of the positive test, and are reminded to take precautions.

When truly bad news comes – say, a positive human test for Zika -- staff visit with the patient at their home and identify any areas of concern for mosquito activity on their property. 

Why we don't aerial spray

When mosquito-borne diseases make news, many densely populated areas – cities – will call for aerial spraying for mosquitos, and some folks wonder why Collin County does not.

The answer lies in the simple fact that rural areas of the county are much less dense than, say, Plano or Frisco – where aerial spraying might be effective in some tightly packed developments. Spraying more than 300,000 acres of rural land would have little or no effect, and comes at a steep cost.

With spraying, you've got to literally hit the mosquito with the spray to be effective at all. In the country, aerial or truck spraying would have little or no effect. The Culex mosquito, for example, flies at dusk and dawn. The Aedes mosquito is a daytime flyer.

What our staff does do about mosquito environments is apply anti-larval pellets on bodies of water  located on county land, just as private landowners are encouraged to do. But experts will tell you that a big risk comes from small, stagnant containers, like an old tire, a flower pot, even a puddle of standing water. For more information on mosquito-borne diseases, our Health Care Services offer some common sense ways to protect yourself and your loved ones from West Nile Virus and other types of arboviruses.

And our Epidemiology & Surveillance department post regular news -- Arbovirus Activity Reports -- of any cases cropped up, whether the disease was imported by a human carrier, or mosquitos were the source of transmission.

As of late June, the human case count in 2018 came to three confirmed mosquito-borne cases, one for Chikungunya and two for Zika. None of these confirmed cases involved folks who contracted the disease locally. And, so far, mosquito traps in cities and the county have yet to return a positive lab test for West Nile Virus.

But a relatively mild winter this year could set the stage for a bumper crop of mosquitos, and increase the odds of West Nile activity.