Bird flu in cows spread only through mammary tissue, not respiration, officials say

Being from just north of Missouri, "Show me!"

I’m currently suffering with a miserable case of COVID-19 (the old pandemic), which I picked up on my trip to the Midwest last weekend. When I came across this headline this afternoon quoting Dr. Eric Deeble, the USDA acting H5N1 response team advisor, I though perhaps I had hallucinated. Here are quotes from the sections that really surprised me related to bovine transmission of the H5N1 virus:

The U.S. Department of Agriculture said Tuesday that the strain of bird flu currently circulating among dairy cattle appears to be only transmissible via mammary glands, or udders, rather than respiratory droplets, a finding that gives officials greater optimism about managing the risks facing dairy workers…

“This is principally mediated by milk. This virus has an exquisite fondness for mammary tissue and is expressed in milk,” Eric Deeble, acting senior adviser for USDA’s bird flu response team, told reporters Tuesday…

Deeble told reporters that although H5N1 circulates via respiratory droplets among poultry, none of the studies conducted so far demonstrate respiratory spread among cattle. The virus also does not appear to affect other tissues in an infected cow.

“The disease, while it is H5N1, does appear to operate very differently in dairy cattle than it does in poultry,” said Deeble. “We have no evidence of respiratory transmission in any case involving dairy cattle.”

In sitting through webinars, talking with veterinarians involved in active cases, and considering that at least 8 poultry flocks have been infected remotely, I really struggle to accept that respiratory shedding is not a component in the epidemiology of H5N1 spread between both dairy herds and spread to area poultry flocks.

If Dr. Deeble has access to formal “infection and transmission studies” that demonstrate no respiratory spread, and “failure of the virus to attack any other tissues in dairy cattle”, then the wider research community needs access to that work for review. However, if he is referring to the limited epidemiological risk studies to date to draw his conclusions, I think we need further efforts before making such sweeping conclusions regarding lack of respiratory shedding or additional tissue tropisms.

Regardless of the results, ARS NCAH in Ames, IA has abundant experience performing infection and transmission studies for BSL-3 agents, including SARS-CoV-2 and Influenza A in large animals. My understanding is that such work has been underway for a while. If results are not yet available, could we at least be provided a status report? The entire H5N1 community needs to transparently see whatever infection and transmission work is available in cattle now, with more data added as further work is completed!

John