Millions of U.S. Chickens Have Bird Flu. Are Humans At Risk?

Experts answer questions about the avian flu outbreak in the American Midwest.

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Chickens stand in their cages at a farm near Stuart, Iowa. The rapid spread of bird flu among poultry farms in Iowa led Governor Terry Branstad to declare a state of emergency on Friday.


Millions of chickens and turkeys have been killed in the Midwest this week in a desperate attempt to stop the spread of bird flu.

On Friday afternoon, Iowa Governor Terry Branstad declared a state of emergency after four new poultry farms tested positive for the virus.

The outbreak, which appears to be the deadliest for birds in United States history, has spread to 13 states and across the border into Canada. Humans do not seem to be at risk from this outbreak, but any avian flu has the potential to mutate into a disease as dangerous to people as it is to poultry.

National Geographic asked experts about the current outbreak and how much risk it poses to humans:

What is bird flu?

The influenza virus can infect mammals such as horses, whales, and pigs, as well as people and birds. Different strains tend to prefer different species, though occasionally a strain will jump from one animal to another, as happened when the swine flu infected humans in 2009.  

This current strain, called H5N2, was last seen in birds on the East Coast in 1983 – and resulted in the largest poultry death toll in U.S. history until now, said Stephen Morse, a professor of epidemiology at the Mailman School of Public Health at Columbia University.

Why is an outbreak happening now?

Experts suspect that the outbreak was triggered by wild birds migrating north. Wild birds can be infected with the flu without showing any symptoms, though the virus quickly sickens and kills farm-raised poultry. An infected wild bird could transmit the virus to a farm’s food or water supply, or the farmer could inadvertently bring it in, Morse said.

It’s not clear whether the affected farms had free-range animals that might have been exposed outside, or if they kept their poultry indoors, which should have made it much harder for them to catch the virus, said Andrew Pekosz, an associate professor and bird flu expert at the Johns Hopkins Bloomberg School of Public Health. “How the virus comes from the environment inside those facilities is a bit of a concern, and may suggest that the farmers need to look at their containment measures again,” he said.

Pekosz said he is satisfied with the way the government has been handling the infection and with its flu-monitoring system. The virus was detected quickly, he said, and he thinks officials have a good understanding of the extent of the current outbreak. Since it wouldn’t be realistic to track or kill migratory birds, the virus couldn’t have been contained before it reached farms.

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Sunrise Farms, one of the largest egg-producing farms in Iowa, was the second of 21 farms in the state infected with avian flu. The farm, which hosts nearly 4 million chickens, is now under quarantine.


Is there a chance the virus could jump to people?

There is a small risk that the bird flu could infect a person who comes into direct contact with sick poultry. But “there are no signs whatsoever that this is something that is of imminent threat to humans,” Pekosz said.

However, influenza viruses mutate constantly, exchanging genetic material within themselves and also with other flu strains in people or animals. Public health specialists are always concerned that dangerous strains in animals will mix with human strains, causing widespread illness.

“Avian flu has become a word that causes fear – and it does cause fear for farmers when they see it in their operations – but most of [the strains] are not a threat to human health,” Morse said.

A similar strain has been found in the blood of people in Nigeria and China, but has not caused serious symptoms or spread widely, said Josh Michaud, associate director of global health policy at the Kaiser Family Foundation.

Is there anything people can or should do to protect themselves?

There shouldn’t be any risk to average consumers, Pekosz said. The affected farms are destroying their animals quickly and preventing them from entering the food supply. Moderate heat kills the virus; eating infected chicken isn’t likely to pose a risk if handled properly in the kitchen.

Poultry workers should be taking adequate care to protect themselves against infection, Pekosz said, but hunters need to be careful, too. The carcass and blood of an infected wild bird are loaded with pathogens – both the flu and others – and should be handled with gloves and respiratory protection. Anyone who comes across a dead, wild bird should avoid contact with it, added Pekosz.

This year’s flu vaccine doesn’t need to be altered to add protection against the H5N2 strain, Pekosz said, because the risk to people remains so small.

Could the outbreak impact the food supply?

At latest count, roughly one-quarter of Iowa’s 60 million egg-laying hens had been sickened or slated to be killed – about 5 to 6 percent of the total in the U.S., according to Iowa Agriculture Secretary Bill Northey, speaking at a press conference this week.

The virus is spreading rapidly, with three Iowa farms infected last week and at least 17 more this week. "This is a magnitude much bigger than we've dealt with in modern times," said Northey. A drop in overseas demand for eggs may prevent rising prices, he added, "but we'll probably still see some impact."

Morse said he’s fairly confident that the flu surveillance and poultry destruction on infected farms will eventually end the outbreak.

“Any predictions are really hard when it comes to influenza, but I do anticipate it will come under control if they follow current measures,” he said.

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