LOS ANGELES, Sept. 6 (UPI) -- Suspected human cases of West Nile virus were reported west of the Rocky Mountains for the first time Friday, although it was still not certain that the stubborn mosquito-borne affliction had completed its three-year march across America.
A Los Angeles County woman who developed symptoms of West Nile last month was described Friday as fully recovered as was a Montana woman, but a third female patient remained seriously ill in a Salem, Ore., hospital.
The patients in Oregon and Montana apparently contracted West Nile in the Midwest, and California officials told reporters that they were at a loss to explain how the Los Angeles woman came down with the disease.
"She is unsure how she got the disease. She has no travel history and doesn't recall being bitten by any mosquitoes," Dr. Jonathan Fielding told a news conference in Los Angeles.
The woman, whose name was not released, fell ill on Aug. 10 and was hospitalized two days later with a diagnosis of aseptic meningitis. Although she did not at first appear to have been a likely victim of West Nile, laboratory tests confirmed that she had indeed been exposed to the virus.
Adding to the mystery of how the unnamed woman was exposed to West Nile, health officials have yet to find the virus in animals, birds and mosquitoes in California.
"We have been anticipating the arrival of West Nile virus in California as reports of the disease have progressed steadily westward across the United States," said state Health Director Diana Bontá. "Although we have no other evidence that the virus has arrived, mosquito surveillance and control efforts are being increased."
The 23-year-old patient from Sweet Grass County, Mont., apparently contracted the disease during a visit to Ohio while the Salem woman, identified in news reports as 29-year-old Heather Aldridge, was infected while visiting her hometown of Grand Rapids, Mich.
"She was bitten by mosquitoes in her home state and became ill while traveling there," said state epidemiologist Dr. Mel Kohn. "We want to emphasize that this is not an illness that can be spread from one person to another. Also, the virus has not been detected in any animals or mosquitoes in Oregon."
West Nile virus is common in Africa and the Middle East, but it began showing up on the East Coast in 1999 and has since steadily spread West. Confirmed cases in animals have been reported as far West as Montana and Arizona.
Spread generally by birds and mosquitoes, the West Nile virus is part of the "flavivirus" genus that causes yellow and dengue fever and is closely related to the St. Louis encephalitis virus. It generally produces mild flu-like symptoms known as West Nile fever in humans, but it can also cause the more-serious ailments West Nile encephalitis, West Nile meningitis and West Nile meningoencephalitis, and has been blamed for 43 deaths nationwide.
Ohio, Illinois, Oklahoma and Indiana reported more human cases Friday and a horse in Arizona also was diagnosed with the virus after spending three months in Minnesota.
"The good news is the virus was not contracted here in Arizona," said Arizona Gov. Jane Dee Hull. "The bad news is that we know the virus has been moving west for a number of years."
Acting Cleveland, Ohio, Health Department Director Matt Carroll said Friday that West Nile virus likely was the cause of an 88-year-old man's death on Aug. 29, while an 83-year-old Louisiana woman who had been diagnosed with West Nile died Friday in Orleans Parish.
Louisiana had the most cases of West Nile in the nation with 222 as of Friday, including nine deaths, according to the most recent information released by the Centers for Disease Control; Illinois had 211 reported cases while Mississippi had 104.
A dead crow found on the fabled South Lawn of the White House in late July tested positive for the virus.
Health officials in virtually every state in the nation have been on the lookout for infected mosquitoes, birds and livestock, and have also been aggressively urging citizens to protect themselves and keep their property clear of any potential breeding grounds for mosquitoes such as standing water.
California Gov. Gray Davis signed a measure Friday doubling the fine for failing to get rid of mosquito havens to $1,000, while hunters in Louisiana and other states have been reminded to wear plenty of protective clothing and to keep bug spray handy.
"People should use mosquito repellent containing DEET, and carefully follow the label directions," Pennsylvania Health Secretary Robert Zimmerman said. "We also recommend that people wear long sleeves and pants when possible, and avoid known mosquito habitats at dawn and dusk, which are prime mosquito biting times."
(With reporting by Al Swanson in Chicago and Phil Magers in Dallas)