Tuesday, February 11, 2025

What to Know About the H5N9 Bird Flu Outbreak

The World Organization of Animal Health reported earlier this week that a strain of bird flu known as the H5N9 was found among sick birds in a California duck farm.

While this isn’t the first case of H5N9 in domestic birds, it’s the first time that it was found in poultry; it also caused severe disease among the flock.

The affected farm has since been quarantined.

What Is H5N9? How Does It Compare to H5N1?

Bird flu viruses are classified based on the type of protein they contain. More specifically, the hemagglutinin (e.g. H3, H5) and the neuraminidase (e.g. N1, N9).

Depending on how the two proteins are blended, the virus will affect people and animals in different ways. Mutations elsewhere in the virus also plays a role.

california duck farm
A new strain of bird flu was found on a California duck farm earlier this week

Since last year, H5N1 has been the dominant strain in the U.S., with many variants spread in poultry flocks, wild birds, dairy cattle and pets. At least 67 human cases have also been confirmed.

According to experts, the H5N9 bird flu virus is the result of the H5N1 virus genetically mixing with other influenza viruses inside of birds. This was not surprising as it’s not uncommon for viruses to undergo ‘reassortment’ within hosts.

The USDA said both H5N1 and H5N9 were found among sick ducks at the farm.

S. Tompkins, who leads the Center for Influenza Disease and Research at the University of Georgia said the H5N1 virus is ‘making its way across North America’ and that it can ‘reassort in species that are susceptible to influenza viruses’.

H5N9 Has Been Seen In the Country Before

The H5N9 virus has been found in U.S. birds before but it typically causes milder symptoms.

Some of the earliest cases of H5N9 date back to the 1960s, when the virus infected turkeys in Wisconsin. However, the birds only experienced ‘mild respisratory symptoms’ and ‘a decrease in egg production’.

h5n9 outbreak
The new H5N9 bird flu virus caused severe disease among ducks at the California farm

The strain of H5N9 involved in the recent California duck farm outbreak is different as it’s related to a newer H5N1 variant. The variant, known as H5N1 D1.1, only emerged over the last year in poultry and wild birds.

Virologist Florian Krammer said just because the variant is now detected, doesn’t necessarily mean trouble. He is more worried about the fact that the H5N5 strain was seen jumping from birds to mammals across Canada.

How Big of a Risk Is H5N9 to Humans?

The H5N9 bird flu virus would still need to undergo several key mutations before it is able to spread among humans.

h5n9 virus
So far, there is no evidence that the H5N9 virus can transmit from human to human

So far, there has been no evidence that the bird flu can transmit from human to human, according to the Centers for Disease Control and Prevention. Rather, most cases stem from direct contact with sick animals.

If the H5N9 virus does mutate and spread among humans, however, it will likely be more virulent as people will have less immunity to the virus compared to H5N1.

Brooke Carter
Brooke Carter
Freelance writer who loves dogs and anything related to Japanese culture.
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