A mosquito comes in for a landing.

Associated Press A mosquito takes a bite. Click photo for larger image.

Ouch! is the response.

But to smash or to flick? That is the question.

And the answer appears to be ...

Flick!

After a tragedy involving a Pennsylvania woman and a new scientific report based on her experience, a number of experts now suggest resisting the urge to smack a mosquito because doing so can inject a disease-causing fungus into the bloodstream. Not all scientists agree that it really matters, however.

"I think if a mosquito was in mid-bite, it would be wiser to flick the mosquito off rather than squashing it," said Dr. Christina M. Coyle, of the Albert Einstein College of Medicine in New York City.

Dr. Dawn Wesson, a specialist in tropical medicine at Tulane University, compared this approach to the long-accepted advice for handling tick bites. "Try not to squash the tick in the process of removal," she said. "If infected with Lyme disease, that could result in more of the Lyme microbes being forced into the wound."

However, Dr. Roger S. Nasci, a mosquito expert at a U.S. Centers for Disease Control and Prevention facility in Fort Collins, Colo., doesn't think there is any scientific basis for making this call.

"There are no published data I'm aware of that document the risk of infections by fungus microbes associated with squashing vs. flicking blood-feeding mosquitoes," he said.

The concern with squashing mosquitoes in mid-bite arose when Coyle and a group of associates studied the death of a Pennsylvania woman at the age of 57. She lived in the Allentown area and was hospitalized in 2002 with myositis, which causes muscle and joint pain, weakness and fever.

Doctors found that the woman's muscles were infected with a fungus, Brachiola algerae (B. algerae). Attempts at treatment failed, and she died four weeks later.

Finding this infection in a person was surprising, according to Dr. Luther V. Rhodes III, an infectious disease specialist at Lehigh Valley Hospital in Allentown who treated the woman.

Experts thought B. algerae caused disease only in mosquitoes and other insects. Mosquitoes with the infection have difficulty reproducing and die early. The microbe even has been proposed for use as a "germ warfare" agent to control grasshoppers and other insect pests because it was thought to be harmless in people or other animals.

Since the Pennsylvania woman was the first known person to be infected by the fungus, doctors wrote about her case in an article published July 1 in the New England Journal of Medicine. They had no direct evidence that the woman was infected by squashing a mosquito in mid-bite, Rhodes said. Other factors led them to that conclusion.

B. algerae, for instance, has never been detected in significant quantity in the salivary glands of mosquitoes. West Nile virus, malaria and other diseases that mosquitoes transmit to humans settle in the salivary glands and are injected into a victim's body with a bite.

Anticoagulants in the saliva keep the victim's blood from clotting, so the mosquito can slurp blood without clogging its hollow feeding tube. Anesthetics in the saliva offer the mosquito squash protection, usually keeping the victim from realizing that he or she is being bitten -- unless the bite hits a nerve. Disease-causing microbes flow into victims with the anticoagulants and anesthetics.

But while mosquitoes do not carry much B. algerae in their saliva, the fungus often settles in their intestines and muscles. Cole and her associates concluded that the Pennsylvania woman, or a well-meaning bystander, probably smashed an infected mosquito in mid-bite, smearing infected body parts into the bite.

"When you feel the bite, there's a big temptation to swat," Rhodes noted. "Try to avoid it."

This summer, the Pittsburgh area is having a "moderately severe" mosquito season, much like last year, according to Bill Todaro, an entomologist with the Allegheny County Health Department. Most of the bites so far involve Aedes mosquitoes, which multiply quickly during wet weather.

Aedes bites have been regarded mainly as a nuisance, because Aedes mosquitoes are not known to be important in transmitting West Nile and other diseases, Todaro said. Only one suspected case of West Nile has been reported so far this year in the area -- in northern Allegheny County.

Culex mosquitoes, on the other hand, do transmit diseases, and the Health Department conducts weekly sampling of local Culex mosquitoes for West Nile virus. No infected mosquitoes have been found this season.

Todaro said more Culex mosquitoes will be buzzing around when hot, dry weather sets in, creating the stagnant pools of water that they favor for breeding. The drier weather may bring more West Nile infections, as well, he said.

Both Aedes and Culex mosquitoes can become infected with B. algerae. Todaro was not familiar with the New England Journal report and had no opinion on the flick-or-smash issue.

Wesson suggested a third option, based on the stage of a mosquito bite.

"If [the mosquito] has just started to probe or just started to feed, dislodging her could then prevent delivery of enough of the pathogen -- whatever it is -- to cause infection or infection resulting in disease," Wesson said.

That would be a flick.

However, if the mosquito already is engorged with blood, a victim might just as well let it finish eating. Saliva already has been pumped into the person's body, Wesson explained. Flicking the insect away may do no good. Squashing may make things worse.

Wesson noted a significant downside to flicking rather than squashing.

"Unfortunately, then the mosquito often goes on to bite another person, or bite you again."

Since B. algerae is a common mosquito infection, why haven't mosquito bites been linked to other cases of fatal or nonfatal myositis? Experts do not know.

Cole and Rhodes pointed out that the Pennsylvania woman may have been unusually vulnerable to infection. She was taking immunosuppressive drugs for severe rheumatoid arthritis, which weakened her resistance to infections.

Millions of other people in the United States also take drugs that suppress the immune system, including organ transplant recipients and people on cancer chemotherapy drugs.

Far better than squashing or flicking, all the experts agreed, is avoiding mosquito bites in the first place by using mosquito repellents when outdoors, especially in the evening when they are most active. That's especially important for people with weakened immune systems.

"I'd recommend that immuno-compromised persons use EPA-registered repellents to avoid contact with mosquitoes, thus making the squash-or-flick choice unnecessary," Nasci said.