The West Nile virus has reached Arizona, state health officials announced Monday.
A sample of mosquitoes collected near San Simon in southeast Arizona in late July tested positive for the disease Monday, said Craig Levy, who is in charge of insect-carried ailments for the state Department of Health Services.
So far, though, there have been no reports of the virus in animal or human samples.
"We knew it was a matter of when, not if, we would see the virus," Levy said. "This tells us that our surveillance is working and makes it more important than ever that people take precautions to prevent mosquito breeding around their homes."
That includes eliminating standing water. Even small places such as old tires, cans and jars can provide a breeding ground.
For items such a birdbaths, change the water at least twice a week.
If there are mosquitoes around, particularly at night when they are active, state health officials recommend lightweight clothing that covers the arms and legs and putting on a repellent with DEET, a chemical compound effective in keeping the bugs from landing and biting.
Despite all the talk about West Nile, "the chance that any one person is going to become ill from a mosquito bite is extremely low," said state epidemiologist Bob England.
The symptoms are so mild, most people don’t even know they were infected, he said. For a few, there is a mild flu-like illness for a few days, with eventual recovery.
In rare cases, though, the virus leads to more serious conditions including encephalitis — an inflammation of the brain — or meningitis, which affects the lining of the brain and spinal cord.
Only a few species of mosquitoes carry West Nile, usually picking it up from biting an infected bird, state health officials said. After a few days, an infected mosquito can pass it to humans. It cannot be caught directly from infected birds or other animals.
There are no vaccines and no real treatment, other than dealing with symptoms.
Other types of mosquitoborne diseases like West Nile have shown up in Arizona, England said. Tests of chickens and mosquitoes in Maricopa and Yuma counties have shown the presence of St. Louis encephalitis, and western equine encephalitis was detected in Maricopa, Pinal and Apache counties.