At least for now, chickens, turkeys and other fowl are the only direct targets of the avian flu outbreak that has spread across the U.S. Yet scientists say there is a subtype of the virus that may have the potential to become a human pandemic.
The outbreak, which the U.S. Department of Agriculture says has affected 20 states, has resulted in the destruction of at least 6 million chickens and turkeys and has put upward pressure on poultry prices. It has also triggered fears that much worse could be in store.
Daniel Janies, professor of bioinformatics and genomics at the University of North Carolina at Charlotte who co-authored a paper this year on the spread of an avian influenza, admits it's "hard to say" whether the flu could make the jump from contained to catastrophe. Still, according to his research, bird flu has the potential to be "highly pathogenic and periodically infect humans."
The Centers for Disease Control and Prevention says that human infection, though rare, has been known to happen when people come into contact with an infected bird. Most recently, the H7N9 variant of bird flu infected some people in China, according to the CDC.
"Our work and that of others suggest that H7N9 has pandemic potential," saids Janies, who is also a research associate in the invertebrate zoology department at the American Museum of Natural History, "but we have not seen human to human transmission yet."
Flu pandemics, which are based on how a disease spreads rather than its death toll, have only occurred four times since the beginning of the 20th century, kicked off by the Spanish flu of 1918 that killed about 50 million people. The most recent was swine flu, which "quickly spread across the United States and around the world" in the spring of 2009, according to the Department of Health and Human Services.
This new avian flu subtype, first reported in China in the spring of 2013, hits the human body hard. Federal officials say that many patients experience "severe respiratory illness, with about one-third resulting in a death." The strain still seems to be outside of the United States, but in January it reached Canada from two people who had been in China.
As of March, more than 640 human cases and 224 deaths from H7N9 flu have been reported globally.
Epidemiologists have been worrying about a global pandemic for years. Just this week, philanthropist and billionaire Bill Gates—whose foundation is involved in disease prevention in developing economies—told Vox he was worried about the potential for a global disease outbreak, although he acknowledged that the probability is "very low."
In a normal season, human influenza can kill at least 10,000 and result in the hospitalization of more than 200,000 others in the U.S. each year, according to the CDC. That translates into an economic cost of $14.9 billion in direct medical costs and lost productivity each year. Some estimate this is just a fraction of the damage a severe flu pandemic could create. One study by the CDC puts the economic impact as high as $166.5 billion.
A recent study in mBio looked at the H5N1 avian flu's spread in Egypt, and whether it has the potential to become airborne. It found that the virus there "could rapidly adapt to growth in the human airway microenvironment," but emphasized that such a mutation was not one that "enhanced viral airborne transmission between humans."
In other words, explained Janies, the H5N1 in Egypt is not adapting to become transmitted between humans. Rather, the bug is doing "a better job of deepening the infection" in humans.
However, the question remains whether scientific inquiry and technology can keep pace with mutating viruses. That area at least offers modest comfort, according to Janies.
"We are much better equipped to see, via genetic sequencers, and communicate, via data sharing over the Internet, on viral spread than in the past," he said.