A New Weapon Against West Nile Virus

This season, the CDC recommends a fourth insect repellent to fight mosquito bites.

An aedes aegypti mosquito is shown on human skin.
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Mosquito bites can be more than an annoyance. For the unlucky, getting bitten can lead to West Nile virus, a potentially serious illness that the Centers for Disease Control and Prevention says is very likely underdiagnosed and underreported. With West Nile season getting underway, and mosquitoes and birds recently testing positive for the virus from Philadelphia's suburbs to California, the agency is spreading the word on prevention.

One of the latest developments for consumers is a recently recommended source of protection that guards against mosquito bites: In May, the CDC added IR3535, a chemical used in Europe for 20 years and sold in certain Avon products in the United States, to the list of three other safe and effective mosquito repellents. The others are DEET, picaridin, and oil of lemon eucalyptus.

The CDC suggests sticking with the four recommended types of insect repellents rather than taking a risk on other products that may not work as well. "There's lots of other things out there on the market that generally don't work," says Lyle Petersen, director of the CDC's Division of Vector-Borne Infectious Diseases. "These four are proven." DEET has been used for more than 40 years; picaridin and oil of lemon eucalyptus were added to the CDC's recommendation list a few years ago. Another option is permethrin, a potent chemical that can be applied to clothing, shoes, camping gear, and bed nets—but shouldn't be used directly on the skin.

The repellents should be applied routinely before going outside, since West Nile is most commonly transmitted through the bite of an infected mosquito, especially between mid-July and mid-September, Petersen suggests. "Every single year since 2002, we've had major epidemics" of West Nile virus, says Petersen, who himself had a previous bout with West Nile. The illness is "basically here to stay, and it's something that we need to take precautions for every summer. And it is spread across the entire continental United States." Prior to 1999, the virus did not exist in the United States.

In a report published last week, the CDC estimated that in 2007 there were approximately 175,000 West Nile virus infections. However, just 3,630 cases of West Nile and 117 deaths from the virus, were reported to the agency in 2007, it indicated in the July 4 Morbidity and Mortality Weekly Report.

This year, areas like Bridgeport, Conn., have already reported trapping mosquitoes carrying the West Nile virus. And many jurisdictions have begun spraying pesticides to kill off mosquitoes. Thirteen cases of West Nile have been reported in the United States as of June 24, with no deaths attributed to the illness.

Because serious problems, while rare, can result from West Nile infection, "it's definitely worth avoiding," advises Petersen. He gave U.S. News tips on how to avoid the illness.

Some Facts About West Nile Virus

West Nile is usually spread by infected mosquitoes, which pick up West Nile by feeding on infected birds and can then transmit the illness to people and animals. There are also limited reports of West Nile being transmitted through organ transplants, blood transfusions, and from pregnant women to their babies, the CDC reports. The virus is not spread through touching or kissing.

About 80 percent of people who are exposed to West Nile don't develop symptoms, but about 20 percent end up with West Nile fever, the signs of which typically appear three to 14 days after a bite by an infected mosquito. Symptoms include skin rash, fever, headache, diarrhea, nausea, vomiting, muscle aches, backache, swollen lymph nodes, and lack of appetite, according to the Mayo Clinic.

Most people who get infected make a full recovery. About 1 in 150 people who have West Nile ends up with severe symptoms such as neck stiffness, high fever, stupor, disorientation, tremors, coma, convulsions, vision loss, muscle weakness, numbness, and paralysis, according to the CDC. Most people who experience severe problems such as meningitis, encephalitis, and paralysis "are left with some permanent neurological effects, often severe and incapacitating," Petersen says. People older than age 50 or with weakened immune systems are more likely to end up with serious or fatal infections.