UNT scientist: Spraying, prevention are key to killing West Nile virus-infected mosquitoes

Reports of the West Nile virus spreading throughout the United States concern many citizens in Dallas, Fort Worth, Denton and other Texas cities.

James Kennedy, professor of biological sciences and an aquatic entomologist, is an expert on mosquitoes, which spread the virus.

"We need to be vigilant and aware that mosquitoes are adaptable and they're here to stay," says Kennedy.

Since April, he and graduate student Bethany Bolling have been monitoring mosquito populations in the Texas Parks and Wildlife Greenbelt corridor, which runs north and south along the Elm Fork of the Trinity River, near Aubrey, Denton, Pilot Point and Little Elm.

In August, the scientists were notified by the Texas Department of Health in Austin that the insects they collected tested positive for the West Nile virus. The infected mosquitos were from the currently dominant species present in the Greenbelt area.

"Mosquitoes pass the West Nile virus from one living thing to another," Kennedy says. "The virus is passed from a mosquito to a bird during what's called a blood meal."

Kennedy says once a bird becomes a carrier, the virus could exist inside the bird without harming it. When a virus-free mosquito bites an infected bird, however, it too becomes a West Nile carrier.

"Mosquitoes and birds are carriers of some viruses but not others," he says. "They carry West Nile and other encephalitis-type viruses along with viruses like Dengue and Yellow Fever, but don't carry viruses like HIV."

The West Nile virus is able to reproduce in the mosquito and ultimately gets into the saliva of the insect and is injected during feeding. Typically, this cycle goes back and forth between bird and mosquito, unless a mammal, like a human, is more convenient.

Kennedy says when a mosquito with the West Nile virus bites a healthy person, it normally causes nothing more than flu-like symptoms. People most at risk of a serious reaction are children, the elderly and those with compromised immune systems, he says. In these populations, there is a potential risk for brain swelling and death.

Kennedy suggests a two-pronged approach to reducing the mosquito population and diminishing the threat of disease. He says control and prevention are the keys to addressing the problem. But control methods, such as spraying at night with pesticides, must be scrutinized for safety and should not be applied routinely. Some of the mosquitoes will die, but beneficial bugs that are predators of the mosquitoes will also perish. Kennedy suggests the use of environmentally friendly biocides like Bacillus thuringiensis, a naturally occurring bacteria that can be applied to habitats where mosquito larvae live.

Kennedy also suggests removal of standing water, where mosquitoes breed, from yard drain-age pipes, buckets and birdbaths, or the introduction of Gambusia affinis — also called mosquito fish — to standing water. These fish are top feeders that will kill the insects.

"If you can control the water they breed in, you can control their population," he says. "If you see something wiggling in standing water, it's likely that it's the larvae of a mosquito," he says. "If you see it tumbling, that's probably a pupae, which is a more advanced state of mosquito development."

BY CATHY CASHIO ccashio@unt.edu

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