More than half a dozen states worried about West Nile virus, including Florida, are using climate-based computer models to predict the course of the mosquito-borne disease before a fatal outbreak.

Public health officials usually rely on reports of dead birds as an early warning sign that West Nile is spreading in their region. Scientists say this new method would warn local officials in advance if their counties are at high risk for the virus.

"We look at this as another tool we can potentially use to help us as we try to protect people from catching West Nile," said Bryon Backenson, assistant director of the New York State Health Department's arthropod-borne disease program.

Last year, New York collaborated with NASA and Oxford University to create climate maps based on satellite data to track the virus. Delaware, Florida, Louisiana, Maryland, South Carolina and Virginia have since joined.

In the $504,000 NASA-funded project, state health departments tally the number of dead birds and mosquitoes that test positive for West Nile while NASA satellites pick up weather information like temperature and humidity.

The information is sent to Oxford, which uses a computer program to create "risk maps" showing areas infected with the virus, temperature and vegetable distribution and migratory routes of birds.

State health officials will use the maps to warn counties when they are at high risk for West Nile so they can develop a plan to fight mosquitoes and the virus.

"Risk maps will help authorities take charge and control as well as anticipate the disease," said Oxford ecologist David Rogers, who helped create the maps.

Mosquitoes spread the virus from infected birds to humans, who can then develop deadly encephalitis, or swelling of the brain. Most people develop only flu-like symptoms and some don't get sick at all. Humans cannot pass the virus.

The potentially fatal virus infected 12 people in Florida last year and infected more than 400 horses and 1,000 birds.

Although no one in Florida has contracted the disease this year, 15 horses have tested positive for it.

No vaccine exists for humans, although health officials say a vaccine for horses, while not fully tested, has shown promise.

Experts say the best weapon against the disease is wearing mosquito repellent and long pants and sleeves, and emptying standing water near homes.

The virus is named after the West Nile district in Uganda, where it was first discovered in 1937.

It was virtually unknown in the United States until New York City was stricken in a summer outbreak in 1999, when seven people died and 62 were infected.

Since the disease turned up three years ago, the virus has hit 34 states and the District of Columbia. The total death toll nationwide is 22, with more than 200 people sickened. Last summer was the most severe with 66 infections and nine deaths.

Louisiana has been hardest-hit this year with the deaths of four people and 58 cases of the infection. There are four other cases in other states. Dead birds carrying West Nile have been found as far west as Texas, Oklahoma and Nebraska, according to the Centers for Disease Control and Prevention.

Scientists hope the satellite maps will pinpoint where conditions are ripe for mosquitoes to thrive and where the disease appears to be spreading. They also hope the information will help local communities to respond sooner.

In states like Florida, where temperatures rarely dip below freezing, mosquitoes breed nearly year-round. Satellite imagery shows the northern border with Georgia has denser vegetation and higher levels of West Nile.