Facts about bird flu you need to know

Bird flu is a common disease that occurs every year. Here are the facts about bird flu that you need to know.

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Avian influenza viruses are found in more than 100 different bird species.

H5N1 is a respiratory virus that primarily infects birds. It is one of a group of viruses that cause highly pathogenic avian influenza (HPAI), which has been found in over 100 species of birds. Wild waterfowl such as ducks, geese, swans and gulls appear to be frequent carriers and they transmit the disease to farmed birds such as chickens and turkeys. Outbreaks are most common in the spring and fall when birds are migrating. Wild waterfowl are much less likely to become ill or die from H5N1 than domesticated birds.

Rarely infects humans but is often serious

Avian influenza may have been around for centuries. In 1878, Italian parasitologist Edoardo Perroncito first described an 'avian plague.' In the decades that followed, farmers and naturalists documented several outbreaks, including mass illness and death in live poultry markets in New York City in the mid-1920s. By the 1950s, the phenomenon had been documented on five continents, and in 1959, scientists isolated the first highly pathogenic avian influenza virus: H5N1.

Avian influenza was not considered a threat to humans until 1997, when an outbreak in Hong Kong coincided with 18 people becoming ill with severe flu-like symptoms. Six of them died. This strain of the virus was different from previous H5N1 viruses, suggesting that 'avian' influenza had jumped to humans.

Avian influenza is transmitted to humans through close contact with infected animals.

Infected birds shed avian influenza viruses in saliva, mucus, and feces. Of the few people who have become ill with H5N1, most have been exposed to these agents through work on poultry farms.

Human-to-human transmission of H5N1 has been documented, but it is rare and scientists believe the disease is not easily transmitted that way. Public health officials say you cannot get bird flu from eating properly prepared eggs and poultry.

Bird flu is making eggs more expensive

Occasional H5N1 outbreaks have been a regular feature of the poultry industry, but the problem has gotten much worse over the past three years. A particularly devastating outbreak in the United States began in February 2022. The CDC estimates that more than 108 million birds in 48 states were infected. By October 2024, when the disease had taken hold and flared up again, more than 2.8 million birds had died. The number of deaths from bird flu has certainly been a factor in the rise in egg prices.

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H5N1 has spread to dairy cows.

H5N1 was recently detected in dairy herds—and scientists are worried.
In March 2024, investigators discovered that dairy cows in the United States had been infected with H5N1. For those who study the disease, it was a wake-up call. Avian influenza is rare in cows and has never infected an entire herd. 'Every once in a while, a cow gets infected, but they're not a natural host for influenza A viruses, so this really shocked the field, ' says immunologist Jenna Guthmiller of the University of Colorado.

The virus has since spread to more than 700 cattle herds in the United States. Several farms in California and Colorado have been quarantined, and some states are requiring testing of cows purchased from out of state.

Cows are much larger than birds and shed more biological material that could carry H5N1. The process of bringing them into warehouse-like facilities and milking them with mechanical equipment is raising concerns that infectious waste could spread rapidly through the herd.

Isabella Humphrey

Update 20 December 2024