There's a massive epidemic taking place across the US right now, though you probably haven't even heard about it. Over the last few months, more than 15 million chickens and turkeys have been infected with a deadly form of avian influenza, according to the latest numbers from the Department of Agriculture, and the country's bird disease experts can't figure out how it's spreading.
No one has been able to conclusively determine how the flu is continuing to spread and the effects have been dire. Dozens of countries have introduced bans or restrictions on importing US poultry, including China, South Korea, and Angola, where the US shipped a combined $700 million worth of poultry last year, according to Reuters. There have been no reported cases of human infections, though the Centers for Disease Control and Prevention (CDC) has noted that there is a slim possibility the virus could make the leap. "While no human infections with these [viruses] have been reported worldwide, similar viruses (like Asian-origin H5N1, for example) have infected people in the past," the CDC website reads, though it makes clear that the risk is low. The outbreak started late last year with reported cases cropping up in a few backyard flocks in Oregon and Washington. By the end of January, the virus was found at a commercial farm in California—and since then dozens of commercial and backyard farms have reported infected birds, with the greatest numbers reported in Minnesota. "Everybody is puzzled as to what could explain why large commercial farms seem to be affected," Hon Ip, a microbiologist at the USGS National Wildlife Health Center, told me over the phone. Ip said the H5N2 strain has also been found in waterfowl that have been shown to carry the virus without getting sick. He said there's pretty solid evidence that the wild birds are spreading the bird flu, but there are still many questions about how the virus is getting into farms—particularly the large-scale commercial farms where biosecurity (measures put in place to prevent viruses, bacteria, and parasites from getting anywhere near livestock) is usually quite strict. "The usual suspects in historic outbreaks have been things like the truck that moves your chickens to the slaughterhouse or the truck that provides feed to your farm," Ip told me. "But in the present outbreak, the usual suspects have been ruled out. There have been a number of epidemiological investigations. So now we need to start thinking about some of the more minor routes that may be the cause of the introduction of the virus." Ip said the virus could be infecting flocks through less detectable ways, via insects or rodents that have carried the flu from wild birds into a barn where they could then infect farm poultry. And Ip said once the influenza gets into a commercial operation, where hundreds of thousands of birds are in very close quarters, it can easily spread and wipe out an entire flock. Other researchers have suggested the virus might be airborne and carried through the wind via bits of infected feather or dust, but there are still a lot of questions. In the mean time, the virus shows to signs of slowing down. The governors of Minnesota, Wisconsin, and just last week Iowa, have all declared states of emergency in response to the outbreaks, hoping that disaster response measures might help curb the epidemic. "Not in my years of state government have we had a disaster situation affecting our poultry like this," Iowa governor Terry E. Branstad said during a press conference last week after declaring the state of emergency. "This is a magnitude much greater than anything we've dealt with in recent, modern times." Right now, the USDA's strategy for fighting the outbreak is to cull and carefully dispose of infected birds, closely monitor new cases of infection, and beef up biosecurity measures. Ip said that from his perspective, getting a more detailed picture of where the outbreaks are happening—and whether nearby wild birds are also infected—could hold the answer to discovering how the virus is spreading and how to stop it. "Are there a lot of wild birds that are infected and therefore lots of opportunity to track that into a farm?" Ip said. "Or is there some kind of agricultural practices that may be contributing to the spread?"