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Bird Flu – H5N1 – Status


Epidemiologists have long been concerned that a type of influenza that mainly infects birds, called H5N1, could develop into the next pandemic. So far it has infected relatively few humans but has been devastating to wildlife in local incidents. So far it lacks the ability to attach easily to most human cells and to be transmitted human to human. But it is an influenza virus, and its cousins have those abilities.

Now it is being found in dairy cows in the US. The map above shows the states in which it has been confirmed. Additionally, virus particles have been found in milk in stores. Emphasize “particles.” These are pieces of virus that have been deactivated by pasteurization. (Another of the many reasons to avoid unpasteurized milk, if you’re inclined that way.) No live virus has been cultured from store milk.

The USDA, CDC, and FDA gave a closed briefing today. Eric Topol was there and reports.

Here are the key points:

  1. Confirmation of H5N1 infected dairy cattle herds in 8 statesBut the FDA report yesterday of commerical milk PCR positivity strongly supports that the cattle spread is far wider than these 8 states. Important to emphasize that (PCR) is testing for remnants of virus, not live virus, which would be unlikely with pasteurization. Other tests, assessing potential evidence for any live virus (egg viability and culture), are to be reported by the FDA going forward. Limited culture tests are all negative to date for any live virus in milk.
  2. From the great work of U Arizona evolutionary biologist Michael Worobey who (heroically) analyzed the 239 H5N1 sequences that were released Sunday night for the first time, it was likely a single initiation of transmission from bird to cows. USDA stated they believe teh outbreak in dairy cattle in the US began in late 2023, initially inTexas.
  3. There is confirmation from sequencing of cattle to cattle and cattle to poultry back transmission. Also there is confirmation of asymptomatic dairy cattle with H5N1 infections but the extent of testing is unclear. The cows that have been infected appear to have a mild illness lasting about 2 weeks with discoloration of their milk. More information on the natural history of illness in cows and the proportion who remain asymptomatic are needed. The only documented human case to date was a dairy worker through direct contact that resulted in conjunctivitis.
  4. For the readiness plan in case human transmission does occur, the public officials asserted that Tamiflu would be effective and it has been stockpiled, that gearing up testing would be done and, if necessary, the US could fully shift its annual flu vaccine production to make H5N1 shots at scale. They have 2 candidate H5N1 vaccines in hand that are well matched to the current sequence and there is the possibility to augment vaccine supply via mRNA-nanoparticle production. Nicely summarized by Helen Branswell at STATnews here.It appears very unlikely, but the more the H5N1 is spread unchecked, the bigger the reservoirs and chances for further functional mutations to take hold. So better to plan for a worst case scenario.
  5. Federal order was put out this morning to mandate testing and reporting of cattle infected, measures to avoid further spread.
  6. Routine testing of pigs, which is important due to their potential facilitation of spread to humans, has been negative to date. To date, data we have are based on dairy cattle; little is known or available about beef cattle, but occupational exposure notifications have been put out to dairy farms and slaughterhouses.

In the US, one person, a farm worker, has been infected with the virus, which caused conjunctivitis (“pink eye”). It’s good to see the federal agencies getting on this and getting information out.

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