A: West Nile is a disease native to parts of Africa and the Middle East that is transmitted only by mosquitoes. It was first found in the United States in summer 1999, when it killed nine people and sickened about 80 in the New York metropolitan area.

It is unclear how it got here, although the strain found in New York is much like the strain found in Israel. Over the past two years it has migrated south with birds.

Q: How is it spread?

A: Birds carry the disease and mosquitoes spread it from bird to bird, bird to human, or bird to horse. It is unclear which birds are the best carriers and which mosquitoes are the best vectors.

Q: Should I be concerned for my safety or the safety of my family?

A: It is not usually dangerous, and in most people it appears to produce no noticeable symptoms. Others will suffer flulike symptoms for three to six days. Rarely, it causes encephalitis, a brain infection that can be fatal or cause permanent neurological disability.

The elderly are most at risk for developing symptoms or complications. So are very young children or people whose immune systems are weakened by other diseases, such as AIDS or HIV.

West Nile is an opportunistic infection and is not especially hardy. It is not as tough nor as deadly as eastern equine encephalitis or St. Louis encephalitis, which are found most summers in Florida. EEE, which killed a 9-year-old boy from the Panama City area two weeks ago, kills one to five people in the the state each year.

Q: How does West Nile cause encephalitis?

A: In some people, the virus multiplies in the bloodstream until it becomes strong enough to penetrate the blood-brain barrier, which normally protects the brain from viruses, bacteria and other harmful organisms that infect our bodies.

Once in the brain, the virus attacks the central nervous system and causes inflammation of the brain, which is encephalitis. Doctors can treat symptoms and make patients more comfortable, but there is no cure. A patient's immune system must fight off the disease itself.

Q: What is the incubation period?

A: Usually five to 15 days from the time of infection.

Q: What are the symptoms of West Nile virus?

A: Flulike symptoms, including fever, aching muscles and fatigue. Latter stages can cause delirium.

Q: Can I catch it from another person?

A: No.

Q: Is my cat or dog at risk?

A: Probably not. According to one published report, the virus was found in a dog in Botswana in 1982. There are no published reports involving cats. The virus was found in a dead cat in New York during the 1999 epidemic, but it's not known if the virus was to blame for its death.

Tests of dogs and cats during that epidemic showed low infection rates.

Q: What can I do to protect myself or my family?

A: First, get rid of any mosquito hatcheries around your home or property. Mosquitoes breed prolifically in standing water, even a tiny amount, so empty anything that holds it. This includes bird baths, old tires, drain saucers at the bottom of flower pots, children's toys and garbage can lids.

Limit time outside when mosquitoes are most active, at dawn and dusk. When outside during these times, wear long pants, socks and long-sleeve shirts and use a mosquito repellent that contains DEET.

Q: What should I do if I find a dead bird?

A: West Nile often announces its presence in a community by killing birds. Blue jays and crows appear most susceptible. If the bird is fresh and obviously has not been killed by something else, call your local health department.

You can also report dead birds online at www.wld.fwc.state.fl.us/bird.

Positive results will be reported, but negative results may not be. The state has tested more than 1,200 birds in the past month. About 30 have tested positive.

Q: Was West Nile to blame for the deaths this summer of dozens of doves in St. Petersburg?

A: No. Those birds died from a disease called trichomoniasis, caused by a naturally occurring protozoan with the scientific name Trichomonas gallinae. Q: I heard about West Nile when it first occurred in New York in 1999, but I heard of no other human cases until it arrived in Florida. What's so special about Florida?

A: That's unclear. However, Madison County, where the two residents have been hospitalized, is prime mosquito breeding ground and appears to provide the virus with an ideal environment. Q: I heard a West Nile vaccine for horses was recently approved and is being shipped to Florida counties where the virus has been found. Is there a vaccine for people?

A: There is no West Nile vaccine for humans and probably never will be. Vaccines are expensive and difficult to develop and grow, and the rate of serious infection appears too low to warrant one. Horses are at much greater risk of sickness or death.

- Sources: The U.S. Centers for Disease Control and Prevention, Florida Department of Health.

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