Scientists take a swat at mosquitoes

By Maggie Koerth-Baker

updated 3:01 p.m. ET June 26, 2008

As storm clouds begin to lift over the flooded Midwest, experts are predicting an entirely different sort of deluge. Mosquitoes, which can breed out of control in the puddles and pools left behind as flood waters recede, may be poised to add insult to injury.

Midwesterners aren't the only ones ripe for the biting. Mosquitoes are ubiquitous in the United States, living in every state and capable of thriving in all kinds of climates, according to Joseph M. Conlon, technical advisor to the American Mosquito Control Association. Wherever there's standing water, there are mosquitoes, he said. And the diseases they carry, such as West Nile Virus, aren't far behind.

But science has some new solutions in the form of improved repellents, genetically modified mosquitoes, and new approaches to vaccine design, as well as some science-based ideas you can put to use at home.

Control just the mosquito
The big strides in mosquito control have largely involved better eradication and population control efforts, aimed to affect only mosquitoes, leaving other animals intact.

One of the most important developments in this effort was bio-rational control materials, said James Stark, executive director of the Metropolitan Mosquito Control District, the public agency charged with keeping Minneapolis and St. Paul relatively mosquito-free. Developed in the 1980s, these "materials" are actually a strain of naturally occurring wetlands bacteria. The District sprays the bacteria onto lakes and other water sources where mosquito larvae hatch and grow. The larvae then eat the bacteria, which kills them by destroying the walls of the insect's stomach. Only mosquitoes and a few related fly species are susceptible. Other animals, including people, can ingest the bacteria without any damage.

LM Otero/AP Mosquitoes are sorted by species and gender before West Nile virus testing. The human form of the disease can cause meningitis or encephalitis, both potentially deadly conditions in the brain.

The project, one of the largest in the world, according to Conlon, has had a lot of success with this bacteria, particularly when combined with newer computer database systems that allow the agency to easily map and track areas where the bacteria are needed most.

But a new method, or, rather, a new twist on an old method, is on the horizon.

Sterile insect technique, or SIT, involves breeding large numbers of sterile male insects and then releasing them into the wild. Ideally, the huge influx of sterile males out-compete their normal counterparts in the game of love, creating a whole generation of unfertilized eggs and crashing the insect population. SIT wouldn't eradicate all mosquitoes, but it would keep population levels low enough to control the spread of diseases.

It's a trick that has worked before on other insects, said James Becnel, research entomologist and lead scientist with the USDA's Fly and Mosquito Control Unit. Those past experiments used radiation to sterilize, but that can be problematic with mosquitoes, making them less able to compete for mates.

Now, an English company called Oxytec is pushing a new approach to SIT, using genetically altered mosquitoes. "They have a gene that's sensitive to antibiotics," Becnel said. "You can rear them in the lab with a small amount of antibiotics and grow big numbers. Then, when you release them, there's no wild antibiotics, so the genes are turned on and they become sterile."

This technique could be coming to malaria-stricken Malaysia very soon, according to an article in the May 21 issue of the journal Nature.

Viral vision
Other efforts focus on controlling the ability of living mosquitoes to spread disease among humans. The most obvious way to do this, of course, is through the use of vaccines. But, while there is a vaccine for the tropical Yellow Fever virus, there aren't any for the mosquito-spread illnesses most common in the United States.

In fact, in the case of West Nile Virus, there's a vaccine for horses, but not for people.

This is a funding issue, said the AMCA's Conlon. "Production and distribution of human vaccines is an extraordinarily expensive process and the time investment from concept to commercial production can be as much as 10 years," he said. "There aren't enough people getting sick to make it worthwhile to a company to develop a vaccine."

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