Hundreds of farm workers exposed to a highly pathogenic strain of bird flu have been offered antiviral medication as a preventative measure in recent days, U.S. public health officials said.
To date, the virulent H5N2 influenza, which has infected turkeys and chickens on Midwestern poultry farms, has not affected humans. But because flu viruses are highly mutable, there is a worry that those in direct contact with infected birds could fall ill from the disease.
How severe such human infections could be is not known. But even if some people become ill, government researchers and public health experts said, it is highly unlikely the illness could be passed between humans - in part due to the genetic make-up of this particular flu strain.
Dr. Alicia Fry, a medical officer in the Centers for Disease Control and Prevention's influenza division, said that while health officials are cautiously optimistic that humans will not be affected, her agency has isolated a pure strain of the H5N2 virus for potential use in a human vaccine, should one be needed.
Concerns about human health risk have prompted investigators to ramp up biosecurity measures on infected farms, with some government staff overseeing the culling of birds wearing full protective body suits and ventilators.
At the same time, the CDC is also working through legal issues related to releasing the government's stockpile of Roche's antiviral drug Tamiflu to be used for this outbreak, agency officials said.
An estimated 300 people in Minnesota, Wisconsin, Iowa and South Dakota have been told they should take the drug as a precaution, public health officials told Reuters, but fewer than half of them have begun doing so.
In South Dakota, all of the infected turkey flocks have been on farms owned by Hutterites, members of a Christian sect that lives and farms collectively, and more than 100 workers there have declined the medical treatment, state officials said.
Elsewhere, workers refusing the drug have said that they do not feel they are at high risk or want to wait to see if they actually get the virus before taking medication, agency officials say.
Economic impact unknown
The outbreak's rapid escalation is fueling concerns among scientists that the virus could become permanently entrenched in the nation's wild bird population.
And agriculture regulators are trying to assess how severe the economic impact will be on the nation's poultry industry.
The United States has boosted the number of people it has put into the field in recent days, from 220 to nearly 365 employees from the Department of Agriculture's Animal and Plant Health Inspection Service (APHIS).
The outbreak also could strain the agency's resources in other ways.
So far, the outbreak has affected more than 7.3 million birds in U.S. commercial flocks. On Friday, an APHIS official told Reuters the department has a pool of $84.2 million in funds available for the outbreak. It is already aware of $60 million in indemnity claims that will be made by poultry farmers seeking compensation for culled flocks.
Meanwhile, in Minnesota, state officials say the virus is being discovered on three to four new poultry farms each day.
Hunt for answers
Iowa, the top U.S. egg-producing state, has seen the largest number of affected birds to date: The strain was identified in an egg-laying facility with 3.8 million hens earlier this month.
Wisconsin, which has to cull hundreds of thousands of birds because of the outbreak, declared a state of emergency last week. Governor Scott Walker authorized the state's National Guard to help contain the disease.
Minnesota, which has seen more than 2.6 million birds affected by the outbreak, soon followed. On Sunday, the National Guard was called up to deliver water for use in the effort to contain the rapidly spreading virus.
One question still unanswered is how the virus is entering poultry barns.
Federal and state researchers are conducting a sweeping research effort to solve the puzzle, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, which is coordinating the study.
One partner in the research is U.S. meat producer Hormel Foods Corp, whose Jennie-O Turkey Store unit has seen at least 29 suppliers hit by the outbreak.
Researchers are examining a variety of factors - dust, wind, wild birds, age of poultry that fall sick and human factors, among others - at farms that have been infected with the virus, and those that have not.
State health investigators say they move quickly once a farm has tested positive for the virus.
Michael Schommer, a spokesman for the Minnesota health department, said state epidemiologists interview everyone working on affected farms to assess their level of contact with infected birds.
Sara Vetter of Minnesota's Infectious Disease Laboratory said her lab has tested 11 individuals who have developed cold symptoms to see if they might be related to avian flu. None has yet tested positive.