U.S. CDC study reveals silent spread of H5N1 bird flu among veterinarians with implications that cases are being undercounted

Medical News: Growing Concern Over Silent Infections
A recent study conducted by the U.S. Centers for Disease Control and Prevention (CDC) has revealed alarming findings about the spread of the H5N1 bird flu virus. The research suggests that veterinarians working with animals may have unknowingly been infected without showing symptoms, leading to concerns that the official tally of human bird flu cases could be significantly undercounted. This Medical News report brings attention to the silent nature of the virus’s spread and the implications for public health.


U.S. CDC study reveals silent spread of H5N1 bird flu among veterinarians with implications that cases
are being undercounted

The study, published on Thursday, examined blood samples from veterinarians and found evidence of antibodies to the virus in several individuals, none of whom recalled experiencing any symptoms. These findings echo previous smaller studies that detected evidence of past infections in undiagnosed farmworkers. According to experts, the ability of the virus to infect people without causing noticeable illness makes it difficult to track its true prevalence and raises concerns about its potential evolution.
 
The CDC Study and Its Findings
To understand the extent of unnoticed infections, CDC researchers attended the annual American Association of Bovine Practitioners veterinary conference in September 2024 in Columbus, Ohio. They recruited 150 veterinarians from 46 states who voluntarily filled out a questionnaire and provided blood samples. Surprisingly, tests revealed that three of them (about 2%) had antibodies against the H5N1 virus, despite not recalling any illness or working with known infected cattle.
 
All three veterinarians with antibodies had worked with dairy cattle, along with other animals, and one had also worked with a flock of infected poultry. This discovery aligns with previous studies that identified undiagnosed bird flu cases among farmworkers. For instance, an earlier study by the CDC tested 115 dairy workers and found that eight (7%) had antibodies suggesting prior infection. Half of them recalled experiencing mild flu-like symptoms but were never diagnosed.

While the number of veterinarians tested in the latest study was small, the findings suggest that many more people may have been unknowingly infected while working with animals. According to Dr. Gregory Gray, an infectious disease expert at the University of Texas Medical Branch, even a low percentage of undiagnosed infections could translate to hundreds or thousands of unrecorded cases nationwide.
 
Implications for Public Health
Experts caution that while the current findings are not an immediate cause for panic, they underscore the importance of continued surveillance. The presence of antibodies suggests that some individuals may develop natural immunity to the virus, which is a positive sign. However, if the H5N1 virus mutates to become more dangerous or spreads more easily among humans, the situation could rapidly escala te into a serious public health threat.
 
Dr. Jacqueline Nolting from Ohio State University, who contributed to the CDC study, emphasizes that increased vigilance is necessary. "Right now, we see that infected individuals are mounting an immune response, which is good news. But if the virus evolves to cause more severe illness or spreads more efficiently, then we have an entirely different and much more dangerous situation on our hands."
 
Silent Spread Raises Concerns
Bird flu has been spreading extensively among wild birds, poultry, cows, and other animals, increasing the likelihood of human exposure. According to the CDC, while the general public’s risk remains low, individuals who have frequent contact with infected animals are at a higher risk of exposure. This includes veterinarians, farmworkers, and others in the agricultural sector.
 
The findings highlight a crucial gap in disease surveillance. The fact that some veterinarians were unknowingly infected suggests that the virus may be spreading in ways that current tracking methods do not capture. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory, acknowledges this challenge: "There is no doubt that the virus has been spreading more widely than official reports suggest. We need to ensure that veterinarians and other animal handlers take the necessary precautions, including using protective equipment."
 
No Data about Viral Persistence and About Long-Term Health Issues
Doctors and researchers are also voicing concerns that no studies have been done for those testing positive for the H5N1 antibodies so see if there is viral persistence in the various ‘body compartments; and also no studies have been done to identify any potential health issues especially in terms of neurological issues.
 
Calls for Better Protection Measures
In response to these findings, experts are urging stricter safety protocols for those in close contact with animals. The CDC advises individuals handling sick or dead birds to wear respiratory and eye protection, along with gloves, to reduce the risk of infection.
 
Dr. Erin Sorrell, a researcher at Johns Hopkins Center for Health Security, stresses the importance of better preventive measures: "This report shows that bird flu can infect people without causing obvious symptoms. Veterinarians and farmworkers should be equipped with proper protective gear and trained in biosecurity measures to prevent infection."
 
Potential for Future Outbreaks
The latest study provides further evidence that bird flu infections in humans may be underreported. Since March 2024, there have been 68 confirmed H5N1 infections in the U.S., most of which were linked to direct exposure to infected animals. However, the actual number of cases could be much higher, given that many infected individuals may not have shown symptoms or sought medical attention.
 
The risk to the general public remains low at this time, but scientists are closely monitoring the virus for any signs of mutation that could make it more transmissible among humans. Experts warn that if such changes occur, the world could face a far more serious public health crisis.
 
Conclusions
The CDC’s findings serve as an urgent reminder that bird flu surveillance needs to be expanded to include individuals who may be infected without showing symptoms. The discovery that veterinarians working with cattle and poultry have been unknowingly exposed to the virus raises important questions about how many cases have gone undetected. This highlights the necessity for more comprehensive blood testing and monitoring in high-risk occupations.
 
While the current risk to the public is considered low, the unpredictable nature of viral mutations means that continued vigilance is necessary. Scientists emphasize that improved surveillance methods, enhanced protective measures, and better reporting systems are critical in preventing future outbreaks. The potential for silent transmission suggests that the virus is spreading more widely than previously thought, reinforcing the need for a proactive approach.
 
The findings also underscore the importance of protective equipment for veterinarians, farmworkers, and others handling animals. Regular health monitoring and increased testing will be essential in identifying new cases early and preventing larger outbreaks. Researchers stress that ignoring these warning signs could lead to serious consequences if the virus becomes more dangerous in the future.
 
Public health officials must ensure that accurate data is collected to assess the full extent of bird flu’s spread. Without proper tracking and reporting, the risk of missing critical developments remains high. The scientific community must work together to prevent any potential crisis before it escalates.
 
The study findings were published in the peer-reviewed journal: Morbidity and Mortality Weekly Report by the CDC.
https://www.cdc.gov/mmwr/volumes/74/wr/mm7404a2.htm?s_cid=mm7404a2_w
 
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