Three U.S. dairy workers have been infected with H5N1 after contact with sick cows, and all of them developed eye symptoms.
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?