California's lone West Nile virus case baffles scientists

Mosquito hitchhiking on airplane considered plausible scenario

By GUY ASHLEY
CONTRA COSTA TIMES

     How, when and where are not the only questions asked by scientists investigating the only documented case of West Nile virus in California.

     Here's two more: first-class or coach?

Scientists say it's possible a Los Angeles County woman who contracted West Nile in August was bitten by an infected mosquito that "hitchhiked" aboard an airplane. The scenario is more plausible because she lives near Los Angeles International Airport and works for a private mail company that handles some air cargo.

     State health officials downplay the possibility, but some experts in mosquito-borne disease are receptive to the idea that California's lone West Nile case was caused by an infectious bug that touched down via cargo plane or passenger shuttle.

     There's historical evidence to show virus-carrying mosquitoes do hitchhike.

     Health officials in Europe and North America have grappled for the past three decades with mysterious cases of malaria among people living close to airports in countries where the disease is not endemic. The World Health Organization has linked at least five "airport malaria" deaths to infected mosquitoes traveling on planes or in passenger luggage.

     Entomologists say several mosquito species were introduced to the United States from Asia and elsewhere after traveling thousands of miles on planes or ships.

     Some even subscribe to the theory that mosquitoes in airplanes, cars or cargo trucks have fueled the rapid U.S. spread of West Nile over the past three years.

     Frederick Murphy, an internationally known virus expert and a UC Davis professor, said he believes hitchhiking is the best explanation for the Los Angeles County case.

     "Mosquitoes are brought into the state aboard airplanes and other vehicles all the time," said Murphy, former director of the Center for Infectious Diseases at the Centers for Disease Control and Prevention.

     State health officials say a number of unlikely events would have had to occur for the Inglewood woman to contract West Nile that way.

     Not only would the bug have had to survive a trip of at least a few hours -- it would also have had to survive outside its preferred humidity long enough to find its prey.

     But every other possible explanation seems to raise just as many doubts.

     "One thing is certain: She was infected by a mosquito," said Vicki Kramer, head of the vector-borne disease section of the state Department of Health Services.

     "Whether it was a mosquito that was imported by an automobile, a truck or an airplane, or a mosquito that picked it up within Los Angeles County, we will probably never know."

     If she had to guess, Kramer said, she believes it's more likely West Nile arrived via a more conventional route: through an infected bird. The bird would then have been bitten by a mosquito that passed it to the woman.

     Kramer said state investigators have all but given up trying to figure out this case's origins. What's more important is that the state gears up for next year, when "we certainly expect to see statewide transmission'' of West Nile, Kramer said.

     Since its arrival in New York in 1999, West Nile has been found in 43 states in the continental United States. So far this year, more than 3,700 West Nile illnesses were reported, and 214 deaths.

     Scientists have been baffled by the Los Angeles case ever since tests first showed the woman had been infected by West Nile.

Health officials say the 31-year-old woman, who has not been named, was hospitalized with asceptic meningitis but made a full recovery.