8 Key Facts About Bird Flu You Should Be Aware Of

Since December 2024, the H5N1 virus, commonly referred to as bird flu or avian influenza, has expanded from California, infecting 58 individuals across seven states. Most of these cases involve farm workers who, as reported by the Centers for Disease Control and Prevention, likely contracted the virus through direct contact with infected dairy cows. Here’s essential information about the disease and its potential risks to the general public.

Over 100 bird species have been identified as carriers of the virus.

H5N1 is a respiratory virus that mainly affects birds. It belongs to a category of viruses responsible for highly pathogenic avian influenza (HPAI), which has been detected in over 100 bird species. Wild waterfowl, including ducks, geese, swans, and gulls, are common carriers and often transmit the virus to farmed birds like chickens and turkeys. Outbreaks typically peak during spring and fall migration seasons. Unlike domesticated birds, wild waterfowl are less susceptible to severe illness or death from H5N1.

Human infections are uncommon but frequently severe.

Bird flu has likely existed for centuries. In 1878, Italian parasitologist Edoardo Perroncito first identified a 'fowl plague.' Over the following decades, numerous outbreaks were recorded, including significant illness and mortality in New York City's live bird markets during the 1920s. By the 1950s, the disease had been observed on five continents, and in 1959, researchers identified the first virus causing highly pathogenic avian influenza: H5N1.

Avian influenza was not seen as a human threat until 1997, when an outbreak in Hong Kong led to 18 individuals developing severe flu-like symptoms, six of whom died. This strain differed from previous H5N1 viruses, signaling that bird flu had crossed over to humans.

Infections in humans remain rare, but the mortality rate exceeds 50 percent. Since 1997, 948 people have been confirmed infected with H5N1, resulting in 464 deaths.

Human infections typically occur through close interaction with domesticated birds.

Birds infected with avian influenza release the virus through saliva, mucus, and droppings. Most human cases of H5N1 have occurred in individuals who had direct exposure to these materials while working on poultry farms.

Human-to-human transmission of H5N1 has been recorded, but it is extremely uncommon, and researchers believe the virus does not spread easily between people. Health officials confirm that consuming properly cooked eggs and poultry does not pose a risk of bird flu [PDF].

The bird flu outbreak is driving up the cost of eggs.

H5N1 outbreaks have been a recurring issue in the poultry industry, but the situation has significantly worsened over the past three years. A severe U.S. outbreak started in February 2022, with the CDC estimating over 108 million birds across 48 states were affected. By October 2024, as the disease persisted and resurged, more than 2.8 million birds had perished.

The surge in bird flu-related deaths has directly contributed to the recent spike in egg prices, which climbed from an average of $1.84 per dozen in September 2021 to $3.82 in September 2024.

H5N1 has recently been detected in dairy cow herds, raising concerns among scientists.

In March 2024, researchers identified H5N1 infections in U.S. dairy cows, a development that stunned experts. Cows are not typical hosts for influenza A viruses, making this outbreak unprecedented. 'It’s highly unusual and alarming for the scientific community,' noted Jenna Guthmiller, an immunologist at the University of Colorado.

The virus has now spread to over 700 herds nationwide. Farms in California and Colorado have been quarantined, and some states have mandated testing for cows brought in from other states.

Cows, being significantly larger than birds, release more biological material that could potentially carry H5N1. The practice of housing them in warehouse-like facilities and using mechanical milking equipment raises concerns about the rapid spread of infectious materials within a herd.

Consuming pasteurized milk is considered safe.

As a precaution, the U.S. Department of Agriculture now mandates that milk processors and transporters test for H5N1. However, the CDC assures that pasteurized dairy products pose no risk of bird flu transmission. Pasteurization, a standard procedure in the U.S., involves heating milk to at least 154°F for a specific duration to eliminate pathogens, and nearly all milk sold in the country undergoes this process.

Unpasteurized milk may contain the virus.

Some individuals prefer raw (unpasteurized) milk, which they obtain from stores, farms, or by owning shares in a cow herd, depending on state regulations. Advocates claim it aids digestion or aligns with their natural lifestyle. However, health experts caution that now is an especially risky time to embrace raw milk consumption.

Raw Farm in Fresno, California, a farm known for its raw milk, has been in the spotlight during the current outbreak. Officials from the California Department of Food and Agriculture detected bird flu pathogens in its products, leading to a quarantine. Raw Farm voluntarily recalled two batches of its products.

A child who consumed milk from the farm developed a fever and vomiting, though it’s unclear if H5N1 was the cause. Additionally, two pet cats that ingested Raw Farm products tested positive for bird flu.

Researchers are worried about the potential for the virus to mutate into a more dangerous form for humans.

Currently, human transmission of bird flu is rare and typically occurs through direct contact with fresh biological material from infected birds. The recent jump of the virus from birds to cows, while unexpected and concerning, likely follows a similar transmission pattern.

H5N1, like many viruses, evolves by mutating and incorporating new genetic material from its hosts. A study in Science by Scripps Research Institute scientists indicated that the strain currently spreading among dairy cows is just one mutation away from efficiently infecting human cells.

However, researchers informed the Washington Post that bird flu is not naturally suited to human cell receptors, and significant hurdles would need to be overcome for H5N1 to mutate into a pandemic-level threat for humans.