West Nile virus battle pits health against hunting

West Nile virus battle pits health against hunting
Sabin Russell, SF Chronicle Medical Writer
Monday, September 29, 2003
URL: http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2003/09/29/MN259293.DTL

Mecca, Riverside County -- West Nile virus, a mosquito-borne illness that has killed almost 100 Americans this year, has just a toehold in California -- it is lurking here, in the dried-out desert marshes at the edge of the Salton Sea.

Soon, that may change for the worse.

Over the objections of local mosquito control experts, hundreds of acres owned by private duck clubs are being flooded, with water pumped from wells, to accommodate bird life for the hunting season.

Predictably, the sparse mosquito population has begun to grow.

Pesticide spraying and other mosquito abatement techniques may keep the disease in check, but Riverside County scientists are concerned. The duck ponds are known for breeding large swarms of Culex tarsalis, the mosquito species that lab studies show is best suited for transmitting West Nile.

"We are going to see an increase in the number of mosquitoes we catch in traps," said Branka Lothrop, an ecologist for the Coachella Valley Mosquito and Vector Control District in Riverside County. "Instead of five or 10 per trap each night, there will be hundreds or even thousands."

Lothrop is concerned that the flooding of the desert marshes will create ideal conditions to boost the virus. "All those hunters are 65 to 70 years old,

and they get covered with mosquitoes," she said. "And building up the mosquito population in the fall cannot be good for the spring."

Culex tarsalis mosquitoes can spend winter with the virus and, unlike other species, can transmit it directly to their offspring through their eggs. They don't need to bite an infected bird to pick up the virus. They can be born with it.

Whether or not the flooding of marshes accelerates an outbreak, the skirmish among scientists and bureaucrats is a prelude to the kinds of problems the state is bound to face when the virus eventually takes hold.

It is an issue that will throw into conflict some of the most cherished values of millions of Californians: environmental protection, recreation and public health.

The flooding of the county's duck ponds comes after months of efforts to push the duck hunting season back. Mosquito breeding slows down as the weather cools, and by Nov. 15, Culex tarsalis enters a natural period of hibernation.

"Even a slight delay would reduce the period required for pond flooding, the potential for mosquito breeding, and the risk of disease transmission and dispersal," Donald Gomsi, general manager of the Coachella Valley mosquito district, wrote in a letter to California Fish & Game Commission Executive Director Robert Treanor on May 8.

Gomsi detailed his arguments at a commission meeting in Long Beach in August. He even carried with him the backing of local duck club owners. But the commission rejected their request. Duck hunting season was set to begin Oct. 18, and the flooding of the marshes has begun.

Sonke Mastrup, deputy director of the California Department of Fish & Game, said it was unclear whether delaying the hunting season would have caused the club owners to delay their flooding of their marshes anyway. "There was a concern that we'd be putting down restrictions without really solving anything, " he said.

Duck club owners had hoped that, by dropping the first two to four weeks of the season in the fall to accommodate the mosquito control effort, they could stretch the season by a like amount in the winter, after it was set to end Jan.

25. But Mastrup said the state is bound by federal regulations -- set by treaty with Canada and Mexico -- that forbid an extension.

Nothing prevents the club owners, Mastrup added, from dropping the first weeks of the duck season on their own. "There is no mandate for them to flood- up. They have the power to choose when and where to do it," he said.

There have been no known cases of West Nile virus transmitted to humans in California this year, but 5,000 Americans in other states have been sickened so far this season, and 95 have died. Striking hardest at those over 50, the virus causes encephalitis, a potentially lethal and often debilitating swelling of the brain, and has produced a frightening, polio-like syndrome in middle-age victims.

California health experts say it is only a matter of time -- this year or next -- before the epidemic washes over the state.

"If you have to wait for an outbreak of disease, that's like calling for a fire truck after your house is fully engulfed," said John Stroh, vice president of the Mosquito & Vector Control Association of California. His group supported efforts to delay the hunting season in the Salton Sea region.

Stroh also is concerned that California's push for wetland restoration is not accompanied by an equivalent effort at mosquito management. "There is tons of money for procuring land and easements but very little for maintenance," he said. Meanwhile, local taxes raised for mosquito abatement are being drained to Sacramento to deal with the statewide budget crisis.

Private duck clubs are not the only ones that flood the Salton Sea marshes in autumn. State and federal wetland managers do the same thing, the whole length of the state, both to accommodate hunters and to provide habitat for birds heading south, along the Pacific flyway, for the winter.

In a 500-acre private duck club in the northeast corner of the Salton Sea, a manager who declined to be identified said duck club owners "have tried to be cooperative" and have been working closely with the Coachella mosquito abatement district. "We, as duck clubs, want to be good neighbors. We don't want our neighbors, or our customers, to get this disease."

He admits he's concerned about his own health as well. "This is prime mosquito time. I got the heck bit out of me the other night," he said.