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Bird flu has been behaving very strangely lately. A strain of the highly pathogenic avian influenza virus (H5N1) has been spreading in dairy cows in at least nine U.S. states. Infected cows have very high levels of virus in their milk, and early reports indicate that it is being spread by contaminated milking equipment, although other methods of transmission are also possible. Several cats that drank raw milk from infected cows developed neurological symptoms and died. Pasteurizing milk appears to effectively neutralize the H5N1 virus.
In recent weeks, three human infections with the virus have been confirmed—all in dairy workers who had contact with sick cows. All three developed symptoms of eye infections known as conjunctivitis. The latest case, reported in Michigan this week, also involved respiratory symptoms more typical of a flu infection. The workers were most likely exposed to the virus in contaminated milk—by getting it on their hands and then touching their eyes, for example, or via milk droplets (or even microscopic particles called aerosols) from a cow’s udder or milking equipment.
“It is really surprising how widespread this thing got over a few months’ time and how this virus seems to be spreading through the milking machines from udder to udder,” says Ron Fouchier, deputy head of the viroscience department at Erasmus University Medical Center Rotterdam in the Netherlands. “This is a completely new situation for all of us, and it’s surprising and a little bit worrying because of the enormous amounts of virus that can be in raw milk.”
But why is H5N1 causing eye infections in humans? And is there a risk the virus could spread more widely and potentially cause a pandemic?
In fact, cases of avian flu causing conjunctivitis are not that rare. There was a large outbreak of H7N7 avian flu in poultry in the Netherlands in 2003, which led to 89 confirmed human cases. Of these, 78 people had conjunctivitis; five had both conjunctivitis and flulike illness and two had only flulike illness. One person developed pneumonia and respiratory distress and died, according to a 2004 study by Fouchier and his colleagues.
“We’ve seen this [conjunctivitis] also before with … H7N7 viruses quite a lot and a little bit less with H5 bird flu viruses,” Fouchier says. (The latter is the type now spreading in cows.) “But we know that these bird flu viruses can cause conjunctivitis rather easily.”
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Matthew Ludak/The Washington Post via Getty Images
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