Why are cow cases worrisome?

Most humans aren’t regularly in close proximity to wild birds or many of the other mammals that have contracted bird flu during the current outbreak.

But cows are a domesticated species regularly in close contact with people on farms. That is troubling to Seema Lakdawala, an associate professor of microbiology and immunology at Emory University.

“I’m always concerned when bird viruses are getting into mammals ... but the cows are concerning because like pigs, they have a really extensive contact network,” said Lakdawala.

Pigs, which are vulnerable to both avian and flu viruses, have long been identified as a potential “mixing vessel,” where bird and human influenza viruses could recombine to create a new strain that spreads more effectively from person-to-person. So far, there’s no evidence this is occurring.

While bird flu has appeared in many mammal species during the current outbreak, cows were not considered likely candidates to catch the disease, experts say. Virologists have long known cattle were vulnerable to influenza type D viruses, but not influenza A viruses like the current bird flu strain, Lakdawala said. Influenza A is one of two main subtypes that typically cause illness in humans.

David Skallnecht, a professor emeritus at the University of Georgia’s College of Veterinary Medicine, said he didn’t expect cattle to catch the virus, but was not terribly shocked that they had.

“I don’t think anyone really saw this coming, but there’s one thing that needs to be clear: As far as susceptibility goes, you can probably infect anything on the planet with flu, if you give it the right dose and the right virus,” Skallnecht said.

The concern now, Lakdawala said, is whether the virus, as it circulates among cattle, could change in ways that make it more transmissible to humans, or from person to person. “It’s not known how the virus will evolve in cattle and whether it will gain some of the mutations that we think of in terms of sensitivity to influenza in humans,” Lakdawala said.

THE DALLAS MORNING NEWS/TNS