Bird flu — or avian influenza, to give it its proper name — is the kind of lurking threat that keeps public health officials awake at night. Luckily, it’s still in the “lurking” column, because the often-deadly disease is not easily contracted by humans, and as far as doctors can tell, it can’t yet be transmitted from person to person.
But because the real threat is that the bird flu virus will mutate into a form that’s better at preying on humans, researchers keep a sharp eye on each flare-up, whether it’s an outbreak that annihilates a hen house or a cluster of human cases. In the past few days, researchers have encountered a bit of both.
In Arkansas, the poultry giant Tyson Foods has been busy slaughtering 15,000 hens that tested positive for exposure to a strain of bird flu. State officials say the birds came into contact with a less virulent strain of the virus, H7N3, which has been known to sicken humans, but hasn’t caused any deaths. The hens are being killed with carbon dioxide gas, and their carcasses are being buried to avoid spreading the disease.
Jon Fitch, director of the Arkansas’ Livestock and Poultry Commission, said officials have a “working theory” on how the hens came in contact with the virus. “The speculation at this point in time was that a large group of Canadian geese made home on a pond very near this facility,” Fitch said. “Our speculation is someone stepped into some of those droppings and carried it into the poultry house” [AP News]. Sounds like a life lesson: Never underestimate the danger of goose poop.
Across the world, in Indonesia, health officials reluctantly announced the death of a 15-year-old girl last month from the dangerous H5N1 form of the virus. Indonesia has had the highest number of bird flu fatalities, a reported 109 out of 241 deaths worldwide. Epidemiologists have raised concerns about the spread of the disease in the Indonesian hot spot, although local health officials claim they have things under control.
[Indonesia's health minister] said only 18 people have been infected in the first six months of 2008, compared to 27 during the same period in 2007 and 35 in 2006 — something she attributed to improved surveillance and public awareness. But the U.N. Food and Agriculture Organization issued a critical statement in March, saying Indonesia’s efforts to control the disease in poultry are failing. The H5N1 virus is entrenched in 31 of the country’s 33 provinces and will continue to kill humans until it can be controlled in birds, it said [AP News].
Finally, an outbreak at a chicken farm in southern England has been called “highly pathogenic,” but only to chickens, not to humans — it’s another example of the less dangerous H7 virus strain. The flock is being slaughtered, and English agriculture officials temporarily banned the movement of live birds in the surrounding area, but those measures weren’t enough to reassure some poultry consumers; Japan and Hong Kong immediately suspended poultry imports from the United Kingdom.
But back to the lurking, insomnia-producing threat: Even though the H7 virus isn’t very dangerous for humans, scientists say it appears to be evolving in our direction. Flu viruses bind to a sugar on respiratory tract cells called sialic acid, which comes in several shapes. Last week US scientists reported that H7 viruses from recent poultry outbreaks in North America are starting to bind the human form of sialic acid, and losing their ability to bind the bird form. Even worse, an H7 was even isolated from a man with the flu in New York in 2003 and it bound most effectively to the human form [New Scientist blog].