Sunday, February 2, 2025

What do we know about bird flu?

There are many influenza viruses. A and B are the main causes of seasonal flu outbreaks and while B only infects humans, influenza A can infect many bird and animal species.

A given influenza virus is identified by two proteins found on its surface, H and N. The common viruses causing winter influenzas are H1N1 and H3N2. The “bird flu” is H5N1.

When bird flu first appeared, it was thought to be a risk primarily to birds and was felt unlikely to infect people. Infecting birds is bad enough: the current outbreak among chickens has been a major cause of diminishing supply and increasing price of eggs. The infected flock must be slaughtered, so chicken also becomes scarcer and more expensive.

The story has gotten worse. H5N1 can clearly spread readily to dairy cattle; there have been major herd outbreaks around the U.S. It can also spread to cats, both wild and domestic and other animals.

From cattle, there has been spread to humans, so far rare and sporadic. Since 1997, there have been about 1000 proven human cases world-wide, reported from 23 countries. More than half of these have died, and this number is clearly an undercount, since testing for H5N1 is not routinely done.

In the U.S. since the start of 2024 there have been 66 proven cases of bird flu, most in dairy workers, and one death. One 13-year-old girl required life support but recovered.

So far, no human-to-human spread has been seen, but as we have learned, viruses mutate, and it would not be a shock for a mutation to appear that would allow this to happen.

Oseltamivir (“Tamiflu”) has been approved to treat H5N1 based on very little data. This drug has been available since 1999 to treat seasonal flu but is not that effective for most patients. Studies have shown that it shortens symptoms of influenza by a day. It does have benefit in very sick influenza patients, reducing the death rate by almost half.

A vaccine is available, but there are only a few million doses stockpiled and if the H5N1 mutates to spread human-to-human, the vaccine may need to be modified.

What should you do?

Avoid raw milk, which transmits H5N1 (as well as many other nasty infections!) and raw meat, and do not feed raw meat to your pets. Pasteurized milk is safe, as is properly-cooked meat.

Do not touch sick birds; call your animal control officer, who will know how to safely handle them.



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