Along Canada's border with the United States, the chickens stand on guard, a thin feathered line newly pressed into duty against a viral foe.
These "sentinel" chickens are the front rank of defense deployed by Canadian health authorities to sound the alarm, should the mosquito-borne West Nile virus cross the world's longest undefended international boundary.
"The chickens serve as one of our surveillance systems," said Harvey Artsob, chief of zoonotic, or animal-borne, diseases at Health Canada's National Microbiology Laboratory in Winnipeg, Manitoba. "The hope is, blood tests on the chickens will provide us early warning if the disease spreads to Canada."
The notion of vigilant platoons of chickens, arrayed at strategic sites along thousands of miles of border might seem comical. For Canada it is part of a serious high alert. The country is girding for what health specialists see as the inevitable surge north of the virus.
The West Nile virus, carried by birds and transmitted to humans by mosquito bites, claimed its first North American victims in New York City last year. This summer, the virus reached New England and spread as far west as Buffalo, just across the Niagara River from Ontario.
"The virus crossed the Atlantic to the U.S.," said Gordon Surgeoner, an entomologist at Ontario's University of Guelph. "To think it won't cross a river to Canada is dreaming."
The West Nile virus, named after the district in Uganda where it was isolated in 1937, has killed eight people in New York, has sent at least 65 others to hospitals and has infected thousands in the city, which recently canceled a Central Park concert for fear of mosquitoes.
"Those are tough New Yorkers running scared," said Marie Douville, a public health physician in Quebec. "So it's no wonder we Canadians are nervous behind our chickens. We're already warning elderly people to stay indoors in the early mornings and early evenings, when mosquitoes are most active."
Most humans infected by the virus suffer only minor flu-like symptoms, such as fever, headache and muscle stiffness. More serious cases, which usually occur in the elderly or those with weakened immune systems, can produce stupor, convulsions and paralysis. Death would come from encephalitis, or severe swelling of the brain.
The virus, which since the 1950s has caused epidemics in Israel, South Africa and Romania, has made it to Massachusetts and Connecticut, although so far it has not made the leap from birds to humans in New England.
Canada's "chicken line" stretches from New Brunswick's St. Croix River valley, which forms its border with Maine, to the Saskatchewan grasslands, opposite Montana. Public health officials say that there is almost no chance that the virus could travel farther west, at least this season.
Military-like secrecy surrounds the 360 chickens, stationed in mesh wire cages at critical junctures near the border, along migratory bird routes or near habitats known for mosquito infestations.
Authorities will not allow U.S. journalists to view the chickens. They say the media might "contaminate" the fowl or compromise the guard sites. However there is suspicion that Canada, hypersensitive about its image south of the border, really just wants to avoid pictures of its wattle-beaked, dirt-scratching, swivel-necked sentries from appearing on front pages of U.S. newspapers or, worse, CNN.
Chickens make good soldiers against the West Nile virus because, unlike hawks or humans, they do not succumb to the enemy. Instead, their bodies manufacture antibodies, which can be detected in weekly blood tests undergone by every guard fowl. Presence of the antibody is proof that disease has arrived.
"Canada has a 25-year tradition of using chickens as sentinels against certain disease," said Randy Gadawski, chief entomologist for the department of Insect Control in mosquito-ridden Winnipeg. He noted that chickens were successfully put on guard against invasions of two other exotic diseases, western equine encephalitis and St. Louis encephalitis.
The West Nile virus is carried by birds, but spread from bird to human by the bite of mosquitoes. There are 73 species of mosquitoes in Canada, and 126 in the United States, but, so far, only Culex pipiens, or the northern house mosquito, has been found transmitting the disease.
Canada has already suffered a West Nile casualty _ one of those fatally stricken in New York last year was a man, 75, from Toronto.
As in the United States, health authorities in Canada are scouring urban parks and the countryside for dead birds. The West Nile virus is wreaking havoc among many North American bird species, including crows, sparrows, bluejays, mallards, robins and red-tailed hawks. Other species, like pigeons, are immune.