How the Bird Flu Sweeping Through US Flocks Is Different Than Past Outbreaks

— -- The ongoing outbreak of avian flu has prompted four states to declare a state of emergency and 40 million birds being either infected or culled as a result. An now, Minnesota has canceled its poultry shows at the state fair to protect its prize fowl.

But this outbreak is different from previous outbreaks, some of which have led to human infections in other parts of the globe, experts said.

There are multiple strains of the virus in the H5 family affecting birds -- nearly all of them in the H5N2 strain, according to the U.S. Department of Agriculture.

The U.S. outbreak has been devastating to farmers, with tens of millions of birds culled in an effort to head off the virus. The outbreak has already cost $1 billion in the economies of Minnesota and Iowa, which are two of the hardest hit states in the outbreak, according to the Associated Press.

The cost of a dozen eggs has also risen 58 percent, up to $1.88 in parts of the Midwest, according to the AP.

In the Far East and parts of the Middle East, bird flu has also led to fatal human infections, experts said. On the other hand, in the U.S. outbreak, no human has been reported infected with the virus in spite of the large spread of the disease across the nation.

Dr. William Schaffner, an infectious disease expert from Vanderbilt University School of Medicine, said in previous outbreaks in Asia, where a version of the H5N1 virus wreaked havoc in the mid 2000's, people were in much closer contact with their animals than in the U.S.

The virus lacks the ability to infect human beings easily, said Schaffner, explaining that the virus cannot attach well to the cell in the throat area to infect humans. "Their attachment doesn't fit into the receptor sites of upper part respiratory tract," he said.

The problem occurs when people are in very close contact with their birds -- living cheek-by-jowl with them almost like pets. In those conditions the virus can eventually reach further into their respiratory tract, Schaffner said.

"In those intense exposures [the virus] gets deep into someone’s chest and makes someone sick," said Schaffner. "Even if it’s in that person, it does not readily spread" to other people.

A human infected with avian flu can face severe flu-like symptoms, including high fever, severe respiratory infection and pneumonia, Schaffner said, noting that the fatality rate can be extremely high -- as high as 30 to 40 percent.

While the H5N1 virus was first detected in Asia, it has recently caused an outbreak in Egypt, where 119 people were found to be infected with the virus and 30 died as a result since the beginning of this year.

A genetically different version of an H5N1 virus has recently been found in wild birds in the U.S. and is considered low risk to public health, according to the U.S. Centers for Disease Control and Prevention. After the initial outbreak of H5N1 in Asia, the CDC has stockpiled some version of a human vaccine for the virus in case of a pandemic, but Schaffner said that would likely be a stop-gap measure until a better, more precise vaccine could be developed to counter whatever mutations the virus has picked up.

Another strain of avian influenza is H7N9, which also was first detected in China in 2013. In that initial outbreak, the CDC reported 132 human H7N9 infections, with 44 deaths.

Dr. Stephen Morse, an epidemiologist and infectious disease expert at Columbia University Mailman School of Public Health, said that the newer H7N9 virus could be a problem if it spreads from person to person more easily.

"H7N9 might be better able to get into the population and spread," said Morse, but he clarified that has not been definitively proven.

The U.S. Department of Agriculture is already testing a vaccine to protect birds in the current outbreak, but Morse said that is not always the answer because of the expense and labor involved.

"You're talking about immunizing billions of animals that are going to live for six months before you send them out," to be culled, Morse noted. "It’s a big, expensive and laborious operation."