A Bird-Flu Pandemic in People? Here’s What It Might Look Like.

The bird flu outbreak in dairy cattle has so far spilled over to just three farmworkers in the United States, as far as public health authorities know. All of them have had mostly mild symptoms.

But that does not guarantee that the virus, called H5N1, will remain benign if it begins to spread among people. Accumulating evidence from the animal world and data from other parts of the globe, in fact, suggest the opposite.

Some dairy cows never recovered from H5N1, and died or were slaughtered because of it. Infected terns seemed disoriented and unable to fly. Elephant seal pups had trouble breathing and developed tremors after catching the virus. Infected cats went blind, walking in circles; two-thirds of them died.

“I definitely don’t think there is room for complacency here,” said Anice Lowen, a virologist at Emory University.

“H5N1 is a highly pathogenic type of influenza virus, and we need to have a high degree of concern around it if it’s spilling over into humans,” she said.

In ferrets experimentally inoculated with the virus through their eyes — the presumed route of infection in the U.S. farmworkers — the virus rapidly spread to their airways, lungs, stomach and brain, according to a report published on Wednesday.