Could that summer cold actually be bird flu?
Key Takeaways
Bird flu is spreading among cattle on U.S. dairy farms, with 189 herds affected and 13 human cases reported, though the true number may be higher.
A study found that 14.3% of farm workers tested had antibodies for H5N1, indicating undetected infections and suggesting that bird flu is more widespread than reported.
Limited testing and stigma prevent full understanding of the outbreak, increasing the risk of more dangerous flu variants emerging from reassortment.
Bird flu is spreading among cattle on dairy farms across the US.[] The outbreak was first detected on a Texas dairy farm in March.[] On March 25, the United States Department of Agriculture (USDA) announced that multiple cows had tested positive for highly pathogenic avian influenza (HPAI) but that there was little risk to the public.[] Since then, the outbreak has affected 189 dairy herds in 13 states and sickened 13 people, according to the Centers for Disease Control and Prevention.[]
Scientists suspect that the true case count is much higher than reported. A new study, published on medRxiv, investigated H5N1 activity on two Texas dairy farms.[] The researchers discovered that 14.3% of the farm workers who participated in the study tested positive for H5N1-specific antibodies, which suggests they were previously infected with bird flu.
The researchers believe that bird flu may be more prevalent than official numbers suggest. “There are definitely anecdotal reports of sick farm workers on implicated farms who were not tested,” Amesh Adalja, MD, an infectious disease expert and Senior Scholar at the Johns Hopkins University Center for Health Security, tells MDLinx.
Bird flu is likely more widespread than records show
To better understand how bird flu spreads, the researchers traveled to Texas's two dairy farms nicknamed Farm A and B.
The farm workers estimated that 4.75% of the cattle on Farm A and 14% of the cattle on Farm B had shown signs of respiratory disease, including coughing, nasal discharges, difficulty breathing, and fever. Milk specimens and nasal swabs later revealed that a significant portion of the cows had traces of the virus in their milk and saliva. On Farm B, for example, 64% of milk specimens collected from 14 cows tested positive for the virus.
The researchers took blood samples and nasal swabs from 10 workers on Farm A. Seven people from Farm B provided a nasal swab, and four gave blood samples. None of the participants tested positive for bird flu via nasal swab. The research team found that two of the 14 individuals, or 14.3%, who gave blood tested positive for antibodies targeting H5N1, which indicated that they were previously infected. These two individuals confirmed that they had flu-like symptoms. One of the individuals who worked directly with cattle on Farm A had a cough, while the other, who worked in Farm A’s cafeteria, had a fever, cough, or sore throat.
According to the researchers, the findings suggest that bird flu is going undetected in people who work on affected farms.
Here’s why cases may be undetected
Widespread testing of farm workers and cattle would help identify cases so that infected individuals and animals can quarantine and avoid spreading the virus to others. However, testing has been limited so far, according to Dr. Adalja. “There is great reticence among some to be tested given the stigma and economic implications of cases being found on a specific farm,” he says. As the study points out, there’s widespread concern that conducting research and testing could negatively impact the dairy business.
Some farm workers have likely contracted the bird flu without knowing it, as shown by the study. This can happen through direct contact with sick cows. According to the Association of American Medical Colleges, a person can absorb the virus through their eyes, nose, or mouth from handling an infected cow’s milk or udders.[]
According to Oladele Ogunseitan, PhD, Distinguished Professor of Population Health & Disease Prevention at the University of California, Irvine Joe C. Wen School of Population & Public Health, H5N1 infections may cause typical flu-like symptoms, including fever, headache, and muscle aches. As a result, people might not seek care or get tested.
Despite common perception, symptoms aren’t the best determinant of infection, according to Benjamin Neuman, PhD, a virologist and professor of biology at Texas A&M University. Symptoms can be minor, but they also change during the course of infection. Plus, people have different thresholds for noticing when they’re sick, and some, due to factors like genetics and underlying health conditions, may develop more severe illness. “What is mild for one person can be severe [for] another,” he says.
When cases go undetected, public health officials won’t be able to understand the full scope of the problem, including how easily humans get infected, how severe the disease might be, and how the virus evolves over time, Dr. Neuman adds.
How missed infections could lead to a more dangerous variant
If a person is infected with multiple strains of influenza simultaneously, these viruses can combine and create a new hybrid virus.
While there’s no evidence that the current H5N1 strain is spreading among people, a new variant could be able to.[] According to Dr. Adalja, this is why health officials encourage farm workers to get vaccinated against the seasonal flu each year.[] If farm workers, for example, don’t get vaccinated against seasonal influenza, they might contract the seasonal flu and bird flu at the same time, leading to a new variant—a phenomenon called reassortment. “Its results can be unpredictable, and that is what worries scientists,” Dr. Neuman says, adding that reassortment is thought to be what led to the 1918 flu outbreak and the H1N1, or swine flu, outbreak in the early 2000s.
The more H1N1 spreads among animals—and birds, animals, and humans—the greater the risk of more virulent strains emerging, Dr. Ogunseitan says. “The danger is that repeated infection of humans, and frequent spillover of infections from birds to cattle to people, may create new strains of H5N1 that may become even more dangerous through person-to-person transmission,” he adds.
What this means for you
Bird flu is spreading among cattle on U.S. dairy farms, with 189 herds affected and 13 human cases reported, though the true number may be higher. A study found that 14.3% of farm workers tested had antibodies for H5N1, indicating undetected infections and suggesting that bird flu is more widespread than officially reported. Limited testing and stigma surrounding the virus prevent a full understanding of the outbreak, increasing the risk of more dangerous flu variants emerging from reassortment.