West Nile season is here

Of 62 different species of mosquitoes found in the state, only three carry the virus, said Lisa Coburn, Oklahoma State University senior agriculturalist.

Coburn has been part of an effort to study the particular mosquitoes that are known to carry West Nile virus since the state’s first cases in 2002.

Oklahoma saw an increase of human cases of West Nile virus in 2006, and a decline in equine cases, according to Oklahoma State Department of Health records.

“We had 48 human cases last year that were reported to the state health department,” said Dr. Kristy Bradley, deputy state epidemiologist and public health veterinarian. Bradley noted there were only two laboratory confirmed equine cases in 2006.

The disease is more likely to affect infants, adults over the age of 50 and those who have a compromised immune system.

“We had the highest fatality rate that we have seen with West Nile since it entered the state in 2002,” Bradley said. “We had six deaths last year from West Nile encephalitis.”

All six were 70 years old or older, she said.

“It underscores the importance of older adults taking mosquito bite precautions,” Bradley said. “The take-home message is that West Nile virus season is here. Take the necessary precautions. Drain any unnecessary standing water around your home if possible.”

Mosquitoes live in garages, vegetation in flowerbeds and rain gutters, as well as culverts and storm water drains.

The floodwater mosquito that has been in the state for weeks, though big and vicious in its bite, does not carry the virus. But it does take a good repellent to keep it away, Coburn said, a product with at least 30 percent DEET.

Coburn suggested looking for repellents in sporting good sections when shopping, and not being overly influenced by claims that any particular product was tested by the military, since the military tests were with the chemical DEET and not particular products.

“DEET is DEET,” she said.

Higher percentages of the chemical mean it will work longer.

Coburn said most of the mosquitoes we see, like the floodwater mosquitoes, are “nuisance mosquitoes.” Her concern is that when the weather changes and becomes hotter and drier, the public will be less cautious and may forget to use repellents at about the time the smaller, quieter and less noticeable mosquitoes that carry West Nile virus start appearing.

“Most people think the noisy buzzing and hard-biting early spring mosquitoes are their real concern,” Coburn said, “when actually the West Nile virus mosquitoes come out later in the year.”

Two common Oklahoma mosquitoes that likely transmit West Nile virus are the southern house mosquito and the Asian Tiger mosquito. The Asian Tiger is the only species in the state that prefers to feed in the daytime instead of the dusk-to-morning habit of other mosquito species. They are generally not prevalent in the state until Oklahoma’s temperatures crank up in July.

Bradley said the West Nile virus originated in regions of Africa and is spread primarily when it is dry and temperatures are high.

The virus was costly and devastating to the Oklahoma equine population when it first hit the state. Though vaccination has effectively brought the disease under control, Bradley does not want anyone to get a false sense of security.

“We know that we will have mosquitoes carrying West Nile virus every summer in Oklahoma,” Bradley said.

She said horses should receive annual booster vaccinations, readily available as over-the-counter products.

The public has a number of misconceptions about the disease and about mosquitoes, Coburn said, with education being a key factor in helping to prevent infection with the virus.

Repellents are readily available that work. Other easily applied common sense measures such as limiting standing water can also limit the growth of mosquito populations.

Bradley said Oklahoma’s wet spring has helped to limit mosquito species that carry the virus, but cases of both human and equine West Nile virus were reported in the state in June last year.

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REPORTER/MEDIA CONTACT:
Janet F. Reeder
Communications Specialist
Agricultural Communication Services
Oklahoma State University
142 Agriculture North
Stillwater, OK 74078
Phone: 405-744-3651
Fax: 405-744-5739
E-Mail: janet.reeder@okstate.edu

Oklahoma State University, U.S. Department of Agriculture, State and Local Governments Cooperating:  The Oklahoma Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, sex, age, disability, or status as a veteran, and is an equal opportunity employer.