To smash it, or flick it? That is the question.

And it now arises when people cross paths with summer's No. 1 outdoor pest - those bloodthirsty mosquitoes.

A new scientific report argues against the knee-jerk response - a lethal smack of the hand -when those blood-suckers insert their needle-sharp feeding tube. It may carry a risk of injecting a disease-causing fungus into the body, according to several experts.

"I think if a mosquito was in midbite, 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.

Dr. Dawn Wesson, a specialist in tropical medicine at Tulane University, said the approach would be similar 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., said there's no scientific basis for making the 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 Dr. Coyle and a group of associates studied the death of a Pennsylvania woman. Age 57, she lived in the Allentown area, and was hospitalized in 2002 with myositis - 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. The infection 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 that B. algerae caused disease only in mosquitoes and other insects. Mosquitoes with the infection have difficulty reproducing and die early. The microbe even was proposed for use as a biological control - or "germ warfare" - agent to control grasshoppers and other insect pests without harming people or other animals.

Since this was the first known case in which the fungus had caused a muscle infection in humans, doctors wrote about it in an article published July 1 in the New England Journal of Medicine.

They had no direct evidence that the woman infected herself by squashing a mosquito in midbite, Dr. Rhodes said. Other factors, however, led them to that conclusion.

B. algerae, for instance, never has been detected in the salivary glands of mosquitoes West Nile virus, malaria, and other diseases that mosquitoes transmit to humans settle in the insects' salivary glands. Only female mosquitoes bite, and the bite injects saliva into the victim's body.

Mosquito saliva contains anticoagulants and local anesthetic substances. The anticoagulants keep the victim's blood from clotting, so the mosquito can slurp blood without clogging its hollow feeding tube. The anesthetics also offer squash protection, usually keeping the victim from realizing that a bite is under way - unless the bite hits a nerve.

Disease-causing microbes flow into the victim's body with mosquito saliva. Although missing from the salivary glands, B. algerae settles into the rest of an infected mosquito's body, especially its intestines and muscles.

Dr. Cole and her associates concluded that the woman, or a well-meaning bystander, probably smashed an infected mosquito in midbite, smearing infected body parts into the bite.

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

Dr. Wesson suggested other options, based on the stage of the bite.

"If she 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," Dr. Wesson said.

However, if the mosquito already is engorged with blood, the victim may just as well let it finish eating. Saliva already has been pumped into the victim's body, she explained. Flicking the insect away may do no good.

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

Dr. Cole and Dr. Rhodes pointed out that the 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 take drugs that suppress the immune system. In addition to rheumatoid arthritis patients, they include organ transplant recipients and people taking cancer chemotherapy drugs.

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

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

Dr. Wesson noted that flicking rather than squashing does involve one big downer.

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

Contact Michael Woods at: mwoods@nationalpress.com.

First Published July 18, 2004, 11:23 a.m.