Return of West Nile Virus Has Health Officials Concerned

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Experts say it is too soon to know just how deadly this year’s West Nile season will be, but they worry that people are no longer as concerned about protecting themselves from the mosquito-borne virus as they should be.

Bird flu may have replaced West Nile in the headlines, but the CDC’s top vector-borne disease expert tells WebMD that West Nile is a much greater imminent threat.

“A couple of years ago everyone was asking about West Nile,” says Lyle Petersen, MD, MPH. “Now it is bird flu. I can tell you with absolute certainty that your bigger fear this summer is West Nile.”

More Than 1 Million Infections

That is because, so far, at least, bird flu is only a threat to humans who have had direct contact with infected birds. West Nile virus is also found in birds, but it is spread to humans by mosquitoes that bite the infected birds and then bite them.

Between Jan. 1 to Dec. 31 of last year, 3,000 cases of West Nile virus were reported in the United States, according to the CDC. Roughly 1,200 people with West Nile had meningitis (inflammation of the lining around the brain and spinal cord) or encephalitis (inflammation of the brain), and 119 people died.

More than a million Americans have been infected since the virus was first reported here in the late 1990s, but only a small percentage of those who are infected develop symptoms.

The elderly are most at risk for serious illness and death, but deaths have also occurred among the very young and middle-aged and younger adults.

Petersen says it may never be possible to predict the severity of West Nile outbreaks from year to year before the peak mosquito-bite months of July, August, and September.

As of late June, two cases of West Nile virus had been reported in Texas this year, with one case each having been reported in Mississippi and Colorado.

“Historically, we have very few cases at the beginning of July and quite a few by the end of July,” he says. “I think we will have a better idea of how things are shaping up by the end of the month.”

Katrina Worries

Fears that major West Nile outbreaks would occur in Louisiana and Mississippi late last summer following the devastation of Hurricane Katrina were not borne out.

Petersen says it appears that the hurricane had little direct impact on West Nile transmissions in the area last year. Torrential rains and flooding may have even reduced transmissions by diluting the stagnant waters that mosquitoes favor for breeding, he adds.

The mosquito that most often carries the West Nile virus typically breeds in small, stagnant, mucky pools of water that are nutrient rich.

That is why the threat to the most severely stricken part of the Gulf may prove to be bigger this year than last.

Outbreaks of West Nile tend to occur when it is hot and dry, rather than when it is very wet, Petersen says.

“We don’t yet know if environmental conditions will favor an outbreak [in the Gulf],” he says. “But if there is West Nile activity in areas where people are still struggling to recover we might see bigger outbreaks.”

Specifically, stagnant water that has collected around debris, which may have been sitting for almost a year coupled with the fact that more people may be outside fixing damaged homes could create the perfect ecological conditions for an outbreak.

Keep Mosquitoes From Biting

Since there is no way to predict when and where outbreaks will occur, the best protection against West Nile virus is keeping mosquitoes from biting, Petersen says.

Any one of three different types of insect repellants can do the job, he says. They are:

DEET. Most commercially available bug sprays contain DEET, which has been used for half a century and is the best studied repellent on the market.

“DEET has a remarkable safety profile and side effects are extremely rare when it is properly used according to the label directions,” Petersen says.

Lemon Eucalyptus Oil. Petersen says this is an effective alternative for people who want a more natural product.

Picaridin. Found in several repellents, including Cutter Advanced, picaridin-based products are not oily like products with DEET and they do not smell. But picaridin products are not sold in concentrations as high as some DEET products, so they should be applied more often.

“If you are going out in the woods for four hours or so I would recommend DEET,” he says. “But for backyard use the other two will work just fine.”

Clothing and tents can also be sprayed with products found in camping stores containing the insecticide permethrin.

And, of course, taking steps to prevent standing water in your yard can keep breeding mosquitoes away.

“The mosquitoes that spread West Nile typically don’t fly very far,” Petersen says. “So getting rid of stagnant water near your home is important. Clogged gutters can breed tons of mosquitoes.”

By Salynn Boyles, reviewed by Louise Chang, MD

SOURCES: Lyle Petersen, MD, MPH, director, division of vector-borne infectious diseases, U.S. Centers for Disease Control and Prevention. 2005 West Nile Virus Activity in the United States. 2006 West Nile Virus Activity in the U.S., June 27, 2006, CDC.