North Carolina has become the seventh state to detect a bird flu outbreak in a dairy cattle herd, and scientists are concerned that the virus could evolve to become easily transmissible to and between humans.
Genomic sequences of the virus from a dairy worker in Texas reveal mutations hinting at adaptation towards mammals. Yet, more mutations are required for the virus to become a human pandemic. It would need to improve its airborne transmission capabilities, like common human influenza viruses.
“We really need to keep on top of this, because I think we are at a bit of a precipice where something interesting or unfortunate could happen,” said Michelle Wille, a senior research fellow at the Center for Pathogen Genomics at the University of Melbourne.
As the virus spends more time in mammals, it could alter its protein to bind with the cellular receptors in human upper respiratory tracts, which could lead to more efficient spread. But the proteins on the virus would also need to stabilize for airborne transmission.
Interestingly, the bird flu affecting cattle is not manifesting as a respiratory illness. “I want to emphasize really how unusual this is,” said Thijs Kuiken, a professor of comparative pathology at Erasmus University Medical Center. “In other mammalian species with influenza viruses, it’s primarily a respiratory disease, which doesn’t seem to be the case in these cattle.”
This suggests that the outbreaks could be a result of “mechanical transmission.” One theory is that the cows are being exposed to the virus during milking, which is supported by the high concentrations of the virus being found in the cows’ milk. Cattle in Texas were found to have been infected with drug-resistant tuberculosis from contact with infected migrant workers.
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