HEALTH – Cows that eat less produce milk that is thicker and yellowish than usual. These are unmistakable signs: they are contaminated by the H5N1 virus, the avian flu virus. In the vast majority of cases, cattle recover happily with some treatment, but the disease continues to spread in herds. In total, 36 flocks in nine different states are today contaminated by avian flu, which is wreaking havoc on birds all over the world.
A worrying progression, even though the first case was only detected at the end of March. Since then, even a human case has been recorded while several cats appear as collateral victims, having drunk milk infected with the virus. The human case was contaminated by cows, and the question is pressing: is it the flu virus, by spreading in cow farms, with the chances of adapting and becoming viral in humans ?
For Nadia Naffakh, molecular virologist and research director at CNRS, “the risk exists because the influenza virus (editor’s note) has a great capacity for genetic variation”. Basically, the flu virus can adapt, and quickly. But the researcher, like the WHO (world health organization), believes that the situation is far from dramatic and that the risk is “low”.
Epidemic in the United States
If what is happening on American dairy farms is worrying, it is because unlike the epidemic affecting seals in Antarctica, it is taking place close to humans. However, each of the potential interactions is an opportunity for the virus to improve its adaptability.
Currently, no one knows exactly how the virus passes from one cow to another. Contact with contaminated milking machines seems responsible for a large part of the transmissions. It is also possible for the virus to spread through the fecal-oral route or through contaminated air. This last track would be particularly worrying because it is much more difficult to contain.
To deal with it, the best weapon is prevention. For the molecular virologist, “all the players seem to have understood the problem and are not underestimating it”. In the United States, the Centers for Disease Control and Prevention has carried out several dozen tests and the health of around 100 people is being monitored. But the tests are not systematic.
Some laborers and farmworkers are reluctant to get tested, due to the cost of care in the United States and a lack of trust in state agencies, even though some are sick. It is therefore impossible to confirm whether it is avian flu or not. Same problem for cows. Breeders do not do tests because they do not want to see their herd flanked by an “infected” sign; it would be bad for business. Problematically, this prevents us from better knowing the extent of the epidemic as well as understanding how the virus spreads.
H5N1, not so dangerous?
When the virus sporadically infects a human, the consequences are known. Catching bird flu is similar to contracting the classic flu: fever and body aches, stuffy nose or congestion. Texas dairy worker diagnosed with bird flu also suffered from conjunctivitis.
Mild symptoms, but bird flu can sometimes lead to death. IN 2024, a child in February in Cambodia and an adult in March in Vietnam died. In total, since 2003, the H5N1 virus is responsible for 463 deaths in 889 cases according to the WHO.
This gives a particularly high mortality rate, but which must be qualified for Nadia Naffakh. “We must be vigilant about this figure already because in the 2000s, it was a strain of the virus different from that of today. Furthermore, a certain number of deaths can be attributed to the lack of access to care in certain parts of the world.. The proof is that the American worker who was contaminated was able to be treated without too many problems.
It appears that the H5N1 strain currently spreading is sensitive to existing antiviral drugs. In addition, vaccine candidates are already being manufactured. “There is better preparation and knowledge of the virus than was the case for SARS-CoV-2”. Unfortunately it is impossible to predict everything. The H5N1 virus remains unknown to the human immune system, which provides much less protection compared to other infections such as winter flu. Also, it is impossible to predict how it could mutate to spread in our bodies.
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