Ever since the West Nile virus reached the United States in 1999, health authorities have assured an anxious public that they could not get sick from contact with dead or dying birds -- only from the bite of mosquitoes that carry the virus from birds to people.
That's still the official word from the federal Centers for Disease Control and Prevention.
While there remains no scientific proof that sick birds can infect people directly, without the aid of mosquitoes, some who work with birds say their experiences suggest they can.
"I think it is possible that people could get it," says Nicholas Komar, a vertebrate ecologist at the CDC. "There is plenty of virus being shed by some species of birds.
"When we make the statement that people are not known to be infected directly [by infected birds], it doesn't mean people can't get infected. It simply states what we know and don't know.
"People need to take precautions and avoid risky behavior. And handling a sick bird with bare hands and no respiratory protection is risky behavior."
State health officials say they have always advised people to use precautions -- gloves, plastic bags or shovels -- when they handle dead birds.
And natural resources officials have urged hunters to wear gloves, to wash up carefully after cleaning or handling game, and to thoroughly cook their kill.
Those advisories are now being underscored.
"Whether it's a virus like this or any other infection, it [West Nile] has brought back to the forefront the things people should be doing all the time," says Mark Shieldcastle, a wildlife biologist with the Ohio Department of Natural Resources. "It should be part of a hunter's daily way of life."
In New York last year, a young technician was cut during a bird necropsy. Days later he was hospitalized with West Nile virus. After a second person was cut this year, the state's wildlife pathologist, Ward B. Stone, ordered everyone in his lab to wear stainless steel mesh gloves sandwiched between three or four layers of latex gloves, in addition to the customary masks, face shields and gowns.
It slows down their work by half. But with thousands of infected birds under the knife, and no vaccines or other treatments to rely on, Stone says, "I think the procedures are important."
Hunters are at risk, too, Stone says. A lot of hunters still dress their kill with their bare hands, just as they did when they were young. "It was unwise when they were young boys to do it that way, and it's still unwise," he says.
Stone advises hunters to use disposable gloves when dressing game; to wash thoroughly afterward with soap and water; to soak their tools for 20 minutes in 5 percent household bleach; and to cook the game thoroughly.
If they're cut, he says, "they should certainly wash the wound out as thoroughly as they can with soap and water, and contact their personal physician for guidance."
Although American crows have been hit hardest by West Nile, birds from more than 110 species have been felled by the virus, including game species -- wild ducks, Canada geese, pheasants, turkeys, pigeons, doves and grouse.
Rabbits and squirrels have also tested positive.
When hundreds, perhaps thousands, of owls, hawks and eagles in the Midwest fell ill with West Nile during the summer, there was speculation that they might have been infected by eating smaller birds slowed by the infection.
There has been no proof. The raptors might simply have been bitten by infected mosquitoes.
But there is growing evidence that West Nile might be spread in other ways.
In 2000, scientists at the National Wildlife Health Center in Madison, Wis., infected nine crows with the West Nile virus in the laboratory. The birds were then placed in a mosquito-free flight room with seven healthy crows. The birds all shared common food, water and perches.
Eight days later, all the infected birds were dead, and the previously healthy crows began to sicken and die.
In a follow-up study recently submitted for publication in a scientific journal, the CDC's Komar repeated the experiment with 18 different species of birds.
"We were able to document direct transmission in four of those," he says -- American crows, black-billed magpies, blue jays and ring-billed gulls.
The healthy birds began to test positive for the virus after five or six days of exposure to the infected birds. "We don't know exactly what the mode of transmission was," Komar says, "but we know it wasn't by mosquito bite."
Other studies have suggested some answers.
"We have done experimental work with great horned owls and American kestrels, and have documented that they do have the virus in their oral cavity and cloacal cavity," Komar says. The cloaca is the common cavity where the birds' digestive, urinary and genital tracts meet.
Birds that touch or feed each other, share perches or come into contact with each others' feces might become infected that way.
Marge Gibson of the Raptor Education Group Inc. in Antigo, Wis., has little doubt that the West Nile virus can be transmitted without hitching a ride on a mosquito.
In August, Gibson took in 30 young common terns that had been orphaned by minks. Housed in a screened enclosure within a screened building, "they seemed active; they had healthy appetites," she says.
But two weeks after the flock arrived, one of the birds fell ill. "It started to have some weakness in its leg -- only one at first," she recalls. Then another tern got sick, "and it became like a domino effect. They just started falling off -- dying."
Tests of one tern brain was strongly positive for West Nile.
Gibson believes she touched off the contagion by hand-feeding an infected hawk and then using an inadequate disinfectant before hand-feeding a tern. "Within a few days [the first tern] began showing limb weakness," she says. The rest of the terns then infected each other, she believes. Only three survived.
Komar was curious about Gibson's terns. "But until her report is presented in the [scientific] literature and evaluated by scientific peers and accepted ... it [the means of transmission] will be just speculative," he says. "It's possible, in a big cage like that, that some mosquitoes do get in."
The larger question is whether people, too, can acquire the virus directly from birds.
Gibson is convinced they can. In September, seven weeks after she began taking in dozens of sick and dying birds, Gibson fell ill.
The first symptoms were headaches and then a curious weakness in her legs. She ran a fever as high as 102.4 degrees and spent days in bed. "I was hot and tired and very slow ... no energy," she says. She began to feel better in 10 days but had a lingering hand tremor.
Her blood tests for West Nile virus were inconclusive, she says. But she believes it was West Nile, picked up from her birds.
Other bird rehabilitation workers have had similar experiences, according to Joe McLeod, a board member at the International Wildlife Rehabilitation Council in Manitoba, Canada. Gibson is a past president of the organization.
"Many of our IWRC members have themselves contracted the virus from their birds and are suffering through the additional strain of becoming ill and still trying to put in 16- to 20-hour days. It is a sad and difficult situation," McLeod says.
Emi Kate Saito, who directs West Nile research at the National Wildlife Health Center, says the rehabilitation workers' experience "certainly needs to be looked into."
"But since these are areas of high [viral] activity, it's hard to say whether it came from birds or mosquitoes," she says.