Nevada appears to have been spared an onslaught of West Nile virus this year and remains one of only four states in the contiguous United States yet to report any cases.

"We missed that bullet," State Veterinarian David Thain said Tuesday.

While isolated cases could still turn up in September or early October, Thain said the chances are lessening as summer turns to fall.

"It's cooling off in the nights enough that mosquitoes are kind of disappearing in numbers," he said. "I think if we do get some cases, it'll be a very small number.

"I'm surprised we haven't had it, but that's just the fickle finger of Mother Nature and the way diseases spread," he said.

Thain said Nevada's expansive desert may have shielded the state from the disease.

"It's a pretty good stretch of desert," he said. "I think that's probably what's acting as a buffer for us. We don't have a lot of cross movement with animals and birds because of the way the Great Basin is laid out."

The Washoe District Health Department plans to treat Reno-area wetlands one more time for mosquitoes on Thursday. The aerial treatments began in May when the potential of the mosquito borne illness making its way to Nevada seemed likely.

West Nile first appeared in the United States in New York in 1999. Since then, it has advanced rapidly across the country. Only Nevada, Oregon, Washington and Idaho have yet to report any cases, according to the National Centers for Disease Control and Prevention.

Mosquitoes pick up the disease from infected birds and transmit it to the people and horses they bite. The virus causes fevers and aches and can lead to potentially fatal swelling of the brain.

Horses vaccinated against the disease will need annual booster shots to retain protection against infection, Thain said.

There is no vaccination for people

So far this year, 3,541 people have been infected with the virus and 66 have died, according to the CDC's Web site. Last year, 4,156 people were infected and 284 died in the largest West Nile outbreak in the Western Hemisphere.

Thain said the Nevada Department of Agriculture will continue testing mosquitoes caught in traps and blood samples drawn from wild horses and sentinel flocks for signs of the disease through early October.

Additionally, people still are being asked to watch for sick or dead birds - specifically ravens, crows, magpies and jays.

"If anyone sees any of those birds that seem ill or just died, we'd like to know about it for West Nile testing," Thain said.

Thain said while Nevada may have escaped the virus this year, it is not immune.

"In all likelihood it'll hit us next year," he said.

On the Net:

Centers for Disease Control and Prevention: http://www.cdc.gov

Nevada Department of Agriculture: http://www.agri.state.nv.us

kolotv.com Extended Web Coverage

West Nile virus Facts

• The West Nile virus is a mosquito-borne virus that can cause encephalitis (an inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord) in humans and other animals.

• The virus is named after the West Nile region of Uganda where it was first isolated in1937.

• The virus appeared for the first time in the United States during a 1999 outbreak in New York that killed seven people.

How is the West Nile virus Spread?

• The virus is spread to humans, birds and other animals through the bite of an infected mosquito.

• A mosquito becomes infected by biting a bird that is carrying the virus.

• West Nile virus is not spread from person to person, and no evidence indicates the virus can be spread directly from birds to humans.

• Only a small population of mosquitoes are likely to be infected and most people bitten by an infected mosquito do not become sick.

• 1 in 300 people bitten by an infected mosquito get sick.

• 1 in 100-150 who get sick become seriously ill.

• 3 to 15 percent of those seriously ill die.

Symptoms of the Virus

• The symptoms generally appear about 3 to 6 days after exposure. People over the age of 50 are at a greater risk of severe illness.

• Milder symptoms include: Slight fever, headache, body aches, swollen glands and/or sometimes a skin rash.

• Severe symptoms include: High fever, intense headache, stiff neck, and/or confusion.

Protecting Yourself

• Control mosquitoes from breeding around your home. Remove standing water from any item or area that can hold water. Standing water is a perfect breeding place for mosquitoes.

• Wear long and light colored clothing.

• Use insect repellent products with no ore than 20-30 percent DEET for adults and less than 10 percent for children.

• Spray repellent on your hands and then apply to your face; spray on clothing, as well. Be sure repellent is safe for human skin and clothing.

• Wash off repellent daily and reapply as needed.

• Stay inside at dawn and dusk because that is when mosquitoes are most active.

Source: www.vdh.state.va.us contributed to this report