Cows wait to be milked at a dairy in Escalon, California. The vast majority of confirmed bird flu cases among humans so far were most likely caused by exposure to either an infected cow or chicken. (Justin Sullivan/Getty Images)
If confirmed, the Tuesday announcement could represent the first Bay Area case of bird flu —the disease caused by the H5N1 virus, also known as avian flu. However, the California Department of Public Health (CDPH) has cautioned that it’s an isolated instance.
The potentially infected child has experienced mild respiratory symptoms and is recovering at home, according to the agency. None of the child’s relatives have tested positive.
Health officials say that no person-to-person spread of bird flu has been detected in California, and that the risk of infection for the general public remains low. But that doesn’t mean that these headlines aren’t still alarming to read.
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More than four years after the start of the COVID-19 pandemic, it can be anxiety-inducing to think about another virus causing a similar amount of havoc. However, the public health experts KQED spoke to say that having accurate information about a virus is one way we can all better protect ourselves against future potential threats.
“H5N1 is really a metaphor for lots of emerging threats in the future where we need to use the lessons we’ve learned during COVID and apply them again,” said Peter Chin-Hong, infectious disease physician at UC San Francisco. “We are being vigilant but not afraid.”
Keep reading for the latest on what researchers know about H5N1 — and how you can think realistically about the risks.
Bird flu, or avian flu, has existed among different bird species for centuries and is caused by the influenza A virus. Most of the time, the influenza A virus sticks to birds, but some strains can jump to other species. The seasonal flu we see each year, for example, is caused by an influenza A virus strain, while another strain of that same virus type caused the 2009 swine flu pandemic that cost tens of thousands of lives around the world.
The number of infected cattle herds across the country continues to grow. The Department of Agriculture (USDA) has confirmed infected cattle in 505 dairy herds in 15 U.S. states since March.
And since the USDA does not require cattle ranchers to test their herds for H5N1, researchers do not even have a complete picture of how far H5N1 may have spread among American cattle.
“The concern about H5N1 has always been there,” said Dr. Jennifer Nuzzo, professor of epidemiology and director of the Pandemic Center at the Brown University School of Public Health. “But in the last couple of years, [the virus] started doing things that have been a bit unusual.”
“We’ve seen this virus start to infect mammals and a wide range of mammals,” she said, pointing at the different outbreaks throughout the world. “That’s a concern because humans are mammals, and so mammals are more like us than birds are.”
But what makes this recent outbreak the most concerning for Nuzzo is that the virus is now capable of infecting cows. “Cows are mammals that humans have a lot more contact with than all the other mammals that we’ve seen get infected,” she said.
So, if H5N1 spreads among cattle, how easily can it infect humans?
At the moment, the vast majority of the confirmed cases among humans were most likely caused by these individuals having previous exposure to an either infected cow or chicken.
But if the virus can jump from cow to human, it still needs to evolve a lot more for it to move from human to human. “Certain mutations are necessary for that to happen,” Dr. Abraar Karan, who studies infectious diseases at Stanford University, told KQED in July. Some of those mutations would allow for “the virus remains stable in the air and that it becomes more efficient at infecting certain types of receptors in human lungs.”
Jon Arizti Sanz, PhD, Postdoctoral Fellow, is preparing for the extraction protocol while in the lab. The Broad Institute, Sabeti Lab, is testing purchased milk at area grocery stores for the presence of bird flu. (David L. Ryan/The Boston Globe via Getty Images)
Soon after public health officials announced that they were investigating two new H5N1 cases in California, Karan told KQED that if the virus continues to circulate in farms, that raises the risk of what he refers to as “viral reassortment.”
Viral reassortment can happen when a human host gets infected with multiple different strains of the virus at once, such as H5N1 and the seasonal flu virus, which are common among humans. “That allows for those strains to exchange genetic material and potentially become more deadly, more transmissible,” Karan explained. “It’s hard to predict what could occur.”
It’s also very complicated for researchers to understand the full extent of the H5N1 virus in the cattle industry. Ranchers aren’t required to test their herds for H5N1, which means experts don’t know how many cows have been exposed to the virus — and consequently, how many humans could now be interacting with infected cattle.
“We haven’t really contained the virus within dairy cows yet,” UCSF’s Chin-Hong said. “And the more it continues in the dairy cows, the more it’s going to probably result in contact with dairy workers.”
Even before the first confirmed human case of H5N1 back in April, the research community pushed federal officials to prioritize the H5N1 outbreak among cattle, specifically to make testing more accessible. On May 30, the USDA announced that it would transfer $824 million from other existing initiatives in order to launch the Voluntary H5N1 Dairy Herd Status Pilot Program.
How dangerous is H5N1 for humans? What are the symptoms?
According to the CDC, signs and symptoms of bird flu have previously included not just conjunctivitis but mild flu-like upper respiratory symptoms, pneumonia requiring hospitalization, fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches and fatigue.
It’s also very important to remember that, according to researchers, the avian flu virus cannot currently spread from human to human. Only people who work in very close proximity to infected animals, like cows or chickens, run some risk.
“If you’re a farmworker,” Karan said, “and you’re feeling symptoms — or feel like you may have the flu — it’s important that you let your doctor or healthcare provider know, ‘Hey, I work pretty closely with animals.’”
What do officials say at this stage? Could we be looking at another COVID-style pandemic?
The CDC said that the risk of H5N1 to the general public “remains low.”
To understand the risk of H5N1, researchers are working to understand the molecular structure of the virus, the way it moves in the air and how human cells respond to exposure. A big part of this work is looking at the genetic information of the virus.
Researchers point out that the overwhelming majority of H5N1 cases in the past two decades show humans caught the virus from animals, not other humans.
“The thing that we’re most worried about right now is the people who work on dairy farms may be exposed to this virus in the course of doing their jobs,” Nuzzo said.
“The challenge in understanding what’s going on right now is that we don’t have very good surveillance on cows,” she said, and “we also don’t have great surveillance on the farms of the people who work there.” She attributed this in part to the fact that “there’s a lot of disincentives for having health officials show up and try to test workers on these farms, [who are] somewhat of a disenfranchised group.”
I heard bird flu was detected earlier this year at a San Francisco market and in local wastewater. Does that mean there’s an H5N1 outbreak in the Bay Area?
San Francisco is one of few hundred cities in the country with a combined sewer system, which means stormwater and sewage flow through the same pipes. When researchers collect wastewater samples, that includes water coming from bathrooms, but it also comes mixed with used water from other parts of the city, including businesses and storm drains.
The timing of H5N1 in the wastewater matched up with two cases of H5N1 among chickens at a live animal market—sometimes referred to as a wet market—in San Francisco. The infected chickens, which were identified by California food safety regulators and showed no symptoms at the time of testing, were removed from the market. Public health officials have also monitored the market workers who were in contact with the chickens.
San Francisco’s health department does not believe that any of the wastewater hits for bird flu are related to human infection. “No one really thinks at this point that the detections are due to human cases of H5N1,” said Dr. George Han, director of the San Francisco Department of Public Health’s communicable disease prevention and control program.
If you go to a live market, will you be exposed to H5N1? The experts KQED spoke to said no. “Surveillance of poultry has been going on for a long time, even before this,” Karan said.
But he nonetheless recommends that if folks can avoid direct contact with poultry in these settings, they should. “But if you’re going to be near these kinds of birds or near their feces or any kind of secretions they may have,” he said, “wear masks, eye protection and wash your hands.”
Is there anything I should practically be doing right now to lower my risks?
Most of the recommendations from the CDC are still just for people who work closely with animals that are vulnerable to H5N1 infections, like cows and chickens. This includes recommending people wear personal protective equipment (PPE) when interacting with infected — or potentially infected — animals.
However, some early recommendations for the overall population include avoiding interacting with sick or dead animals you may find, like wild birds and chickens. One big recommendation from the CDC: That folks avoid consuming “raw milk,” or milk that has not been pasteurized.
Most milk sold in the U.S. is pasteurized, which means that during production, this milk was briefly heated to a certain temperature in order to kill harmful germs that may be present. In April, the FDA reported that 1 in 5 pasteurized milk products nationwide tested positive for the H5N1 virus — but since the pasteurization process kills the virus, any H5N1 found was already dead.
While there haven’t yet been any cases of people getting sick with H5N1 after drinking raw milk, pasteurizing milk still remains a best practice in the industry to ensure the safety of dairy products and kill not just the H5N1 virus but many other viruses and bacteria that can spread through cow milk and make humans sick.
In California, it is legal to sell raw milk, and data shows that demand for this product has continued to grow, even after the CDC’s recommendations. “Everybody in California loves farm-to-table and natural foods,” Chin-Hong said, but he adds that if folks are thinking of consuming raw milk, they should also assess the real risks that come with doing so — especially now, as the U.S. watches for any spread of H5N1.
“Is the juice worth the squeeze?” he asked, “If you are very old or very young, particularly babies under six months or those who are older, that risk might be too high at this moment.”
This story contains reporting by KQED’s Carly Severn, Keith Mizuguchi and Jared Servantez, and was originally published on June 18.
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