The H5N1 avian flu virus, which mainly affects birds, has been well known to health authorities for many years. Although it has primarily affected poultry and some mammals, new research shows that this virus is changing in worrying ways. If this development continues, it could potentially increase risks to human health.
A constantly evolving virus
The virus H5N1 is a type of avian flu that initially primarily affected migratory birds, but has since gradually infected several other animal species, including mammals. Human infections remain rare, but cases have been reported in several parts of the world, often following direct contact with infected birds. Symptoms in humans are generally mild, but experts remain concerned about the virus's ability to mutate and transmit more easily between different species.
A key element of the potential danger of this virus is in fact its ability to evolve. The H5N1 virus was detected in around fifty species of mammalsincluding dogs, cats and even cattle. Although scientists have not observed human-to-human transmission at this time, the possibility of this virus developing the ability to spread between humans remains a threat.
E627K: a worrying mutation
To better understand how the H5N1 virus might evolve and potentially transmit between humans, researchers at the Centers for Disease Control and Prevention (CDC) used ferrets in their experiments. These animals are commonly used in influenza research because of their respiratory physiology similar to that of humans, making them particularly useful for studying the spread of the virus.
In this study, researchers used a sample of the H5N1 virus taken from a worker on a Texas dairy farm. This virus carried a particular mutation, called E627Kwhich attracted the attention of scientists. It is in fact known to improve the ability of the virus to replicate at colder temperatureslike those of the human body, unlike birds where the body temperature is higher. This finding has raised concerns because it could indicate that the H5N1 virus is becoming more able to multiply in a human environment, thereby facilitating transmission between humans.
Transmission between ferrets
To test this hypothesis, the researchers introduced the H5N1 virus directly into the ferrets' nostrils. Result: they developed serious symptoms, such as diarrhea, breathing difficulties, fever and even died in some cases. In contrast, infections seen in humans in the United States have been relatively mild and limited to mild symptoms such as eye irritation or low-grade fever.
A possible explanation for this difference is that the researchers administered a large amount of viruses to ferrets, much higher than that a human would receive in a natural setting. Additionally, humans have some immune protection from previous exposure to related influenza strains, which is not the case for the ferrets used in this study who had never been exposed to such strains.
One of the most worrying findings of this study lies in the transmission of the virus between ferrets. When researchers observed ferrets in contact directthey found that the virus spread easily from one animal to another. Indeed, every pair of ferrets in direct contact showed signs of serious illness, suggesting that physical contact strongly promotes the transmission of H5N1.
The researchers also tested other modes of transmission, such as through contaminated surfaces, by placing a healthy ferret in a cage previously occupied by an infected ferret. This method of transmission as well as airborne spread has proven to be much less effective than direct contact.
A virus to watch closely
Although this study provides crucial information about the spread of H5N1, it also has some limitations. This is because laboratory experiments do not replicate all the complexities of the human immune system nor human behavior and transmission in a natural setting might differ.
Despite these uncertainties, researchers emphasize the importance of continue to monitor the evolution of the H5N1 virus. Although rare, the E627K mutation could be a sign of the virus's adaptation to human temperatures and therefore greater ability to transmit between humans. Even if no human-to-human transmission has yet been observed, vigilance remains essential. Could the H5N1 virus one day become a threat to humanity? The answer to this question may well depend on how these mutations evolve and how they influence the virus's ability to spread.
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