The H5N1 virus, also known as bird flu, has created an enduring crisis this year, massacring millions of birds and other wild animals, while stirring outbreaks in dairy farms across the U.S. But now more and more human cases are being reported, raising the risk of another pandemic like COVID-19. As the number of confirmed bird flu cases continues to climb in various states across the country, many public health experts are anxiously awaiting results from testing performed in Missouri that will determine whether an infected individual passed the virus onto health care workers and a member of the household who later developed symptoms.
A third case of bird flu reported in California this week (with two others pending confirmation) is the 17th confirmed human case in the current U.S outbreak, which began in April 2022, according to the Centers for Disease Control and Prevention (CDC). All but one of these cases have occurred in farmworkers working with poultry or dairy cows who were exposed to the virus. The other occurred in Missouri.
There, someone who didn’t work on a farm became infected with H5N1, the first case of its kind to not have a direct link to animals. This is worrisome because it could indicate human-to-human transmission, which is a key component of any widespread illness, including a pandemic. So far, it seems that most, if not all, human H5N1 cases have involved the virus jumping from animals but petering out before spreading to others. All patients have recovered.
Although the infection was confirmed Sept. 6, the investigation to determine whether the people the individual came into contact with were infected is still ongoing. Yet it’s critical to find out this information quickly to keep the outbreak under control, said Dr. Jennifer Nuzzo, an epidemiologist and director of the Pandemic Center at Brown University School of Public Health.
“There are enough worrisome signs that I think we should be using this advanced warning to try to get ahead of [H5N1] as best we can,” Nuzzo told Salon in a phone interview. “That includes doing a really thorough investigation anytime we find cases to make sure they didn't spread to somebody else and to figure out if there is anything about this virus that's changing in additional ways that we don't want to see change.”
"We cannot rule out that future cases won't be severe."
Most cases reported have been classified as “mild” with symptoms like conjunctivitis (pink eye), fever and respiratory symptoms. In a case study published in the New England Journal of Medicine (NEJM), a man working with dairy cows in Texas who was infected with H5N1 experienced subconjunctival hemorrhage — which means he started bleeding from the whites of his eyes. However, bird flu infections can be more severe and even fatal. The overall fatality rate across H5N1 outbreaks is estimated to be above 50%, but that may be an overestimate due to many milder infections being missed. Regardless, it is not clear how this could change if the virus evolved to transmit between humans.
“We cannot rule out that future cases won't be severe,” Nuzzo said. “We're pinning our entire strategy for responding to this virus on the hope that it's not severe.”
Strategies are being enacted to reduce the spread of the virus: using personal protective equipment (PPE) on farms, increasing testing, and stockpiling vaccines. (An mRNA H5N1 vaccine is being developed, and a bird flu vaccine from Sanofi is also on its way.) Notably, the CDC is urging farmworkers in particular to get the flu vaccine this year because of the risk of co-infection. If multiple virus strains circulate together at once, genetic material could be swapped around in a process called viral reassortment, potentially producing more dangerous evolutions of either virus.
However, all of these strategies should be ramped up, said Dr. Scott Roberts, an infectious diseases specialist at Yale Medicine. The CDC has run around 52,000 specimens that could detect the virus in humans since late February. But a study in Nature last month suggested the contract tracing necessary to mitigate the spread of the virus among infected farmworkers was not being performed and that veterinarians anecdotally reported that testing on farms was lacking.
“I would hope that public health infrastructure and public health leadership here in the United States would have learned the lessons of COVID to really respond to this in a more robust way than it seems they have so far,” Roberts told Salon in a phone interview.
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Some of these strategies have been challenging to implement, with direct health consequences. In Colorado, for example, poultry workers got infected in July because it was 104 degrees Fahrenheit and they couldn’t keep their PPE on properly, said Dr. Abraar Karan, Stanford infectious disease physician and post-doctoral researcher.
“That should never happen,” Karan told Salon in a phone interview. “That is a problem we could anticipate … It’s more logistics and coordination and doing it consistently every single time because if you mess up one time or you let your guard down one time, you can easily be dealing with an outbreak.”
"Every time this virus goes from an animal to a human, it’s giving the virus one more chance to adapt."
The CDC has thus far assured the public that a person’s threat of being infected with bird flu is low if they don’t work with farm animals. In the Missouri case, contact tracing interviews with the infected person "detected that the household contact had been symptomatic with nausea, vomiting and diarrhea with a simultaneous onset of symptoms, implying a common exposure rather than human-to-human transmission," said Dr. Demetre Daskalakis the CDC’s Director of the National Center for Immunization and Respiratory Diseases at a media briefing.
Still, the more the virus spreads, the more chances it has to evolve, said Nahid Bhadelia, an associate professor of infectious diseases at Boston University School of Medicine.
“Every time this virus goes from an animal to a human, it’s giving the virus one more chance to adapt to potentially get better at infecting humans,” Bhadelia told Salon in a phone interview.
Public health experts are concerned that — with 281 dairy herds affected in 14 states and counting — cases are falling through cracks in surveillance systems and increasing those chances. Many farms have reportedly been hesitant to test animals for economic consequences throughout the outbreak. In California, the country’s largest dairy supplier, it was originally estimated that 10% of cows would be infected, but a newsletter from the California Dairy Quality Assurance Program suggests that number could be far higher at 50 to 60%. In a letter published in the NEJM, H5N1 was detected in the wastewater of 10 out of 10 cities tested.
“We've always known that there's likely more cases that have been missed, particularly among dairy farm workers that never were tested,” said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security. “The testing among dairy cattle is not very robust, and the amount of proactive action taken by certain states is not enough to give a lot of confidence that this is being handled properly.”
Human cases are likely going under the radar as well, if, for example, infected people are not going through the health care systems where these cases are tracked, said Dr. Meghan Davis, an associate professor at Johns Hopkins Bloomberg School of Public Health.
“These workforces are often marginalized and this is a lot of migrant and immigrant workers who may lack trust with authorities or not have great access to healthcare and may need extra support beyond what we might be able to do in other workplace settings,” Davis told Salon in a phone interview.
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The CDC is currently testing whether exposed individuals in Missouri have traces of H5 antibodies in their blood to retroactively determine if they were infected. However, the process to create a test that could specifically detect the virus that was genetically identical to the infected patient's is complex and involves reverse genetics, taking the CDC about three weeks, Daskalakis said at the briefing.
"We realize people, including all of us at CDC, are anxious to see results from this testing," he said.
Although many believe the chances are low that there was human-to-human transmission in Missouri at this point in part due to the nature of the index patient’s condition and the symptoms of those exposed, it can’t be ruled out until the final results are made public. There is a lot riding on the findings.
“If this virus gains the ability to spread between people, we would be in a new pandemic,” Nuzzo said.
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