2024-04-13 07:25:46
The avian flu epidemic affecting American farms does not only concern sheep. For several weeks, cases of infection have been detected in dairy cow farms, raising fears of the emergence of a virus capable of adapting to various mammals, including humans.
Article written by franceinfo – Comments collected by Marie-Adélaïde Scigacz
France Televisions
Published on 04/13/2024 09:25
Reading time: 5 min
Dairy cows on a farm in Des Moines (Iowa), in the central United States, October 19, 2019. (CHINE NOUVELLE / SIPA / AFP)
The avian flu epidemic hitting the United States worries specialists. Widespread in poultry farms, the H5N1 virus was detected on Friday April 12 in 24 dairy cow farms across the country. A “jump” from one species to another which makes this epidemic a curiosity and revives concerns about transmission to humans. In Texas, the employee of a dairy farm has already developed a mild form of this avian flu. Although no cases of transmission between humans have been observed to date, specialists are monitoring the situation closely.
To find out more, franceinfo interviewed Benjamin Roche, research director at the Research Institute for Development (IRD) and coordinator of the Prezode initiative, an international network for preventing the emergence of zoonoses (transmissible diseases of animals to humans).
Franceinfo: Why is the current epidemic in the United States different from those we have known so far?
Benjamin Roche: What we observed until then, in France and in the many countries affected by avian flu epidemics, was a significant circulation of the virus, which tended to become globalized, causing a few human cases, very sporadically, mainly in people who work on agricultural operations. This situation remains rare, because we know that viruses circulating in birds have difficulty directly adapting to humans, their immune system being very different from ours.
What is worrying about the current epidemic in the United States is that the virus is starting to circulate in cattle farms. If the virus has adapted sufficiently to circulate in certain mammals, the path to reach humans is shorter than if this virus was only adapted to birds. The main risk is that it adapts to humans until one day being able to circulate from human to human.
The virus has been detected on 24 American farms, in states very far from each other. Could the virus be circulating in other species?
The fact that the cases are quite geographically diffuse may suggest that a large number of events remain undetected and that there are transmission circuits that we do not see. If we can reasonably think that the epidemic is quite diffuse, let us not forget that the United States has excellent means of monitoring and detection. Unfortunately, only time will tell if the outbreak is truly significant.
Finally, a virus may prove highly pathogenic for one species, but not for another. This one, we know, is highly pathogenic for certain species of birds. It has the potential to be highly pathogenic to cattle, but may not be highly pathogenic to humans. These are things that we still know relatively little about. The situations differ depending on the strain, subtype, etc. But when it comes to flu viruses, it’s pigs that worry us most. They have immune and antigen receptors which enable them to replicate fairly well the viruses circulating in birds, as well as those circulating in humans. The pig is the ideal mammal to carry out this “mix” which would produce a virus capable of being transmitted between humans.
Seeing the virus in cattle before having seen it in pigs is an original situation. Here again, it is difficult to know if this is because we have better means of detection today than in the past, or if this is a new fact.
How did the virus jump from birds to dairy cows? Could it be that transmission took place through food given to cows and which, in the United States, may contain poultry, as suggested by some American researchers cited by The Telegraph ?
At this point, this is speculation. To my knowledge, there is no certainty on how the virus jumped between species in this specific case. And knowing this will surely take time.
Are there breeding conditions that favor the spread of viruses?
In birds, we know that intensive breeding is an important factor in the level of transmission. In cattle, as the case is rather rare, we do not have the same level of knowledge of the risk of transmission of avian flu. To my knowledge, there is no specific protocol in cattle for avian flu, other than respecting common sense practices of course, such as cleaning and decontamination of surfaces or regular tests.
You mentioned the importance of preventing the virus from adapting to humans, but how are health authorities working on this?
As we saw during the Covid-19 pandemic, it is good to be prepared and respond in the event of an epidemic, but the best thing is to prevent it, by preventing viruses from reaching to the man. This is what we call “primary prevention”. As early as January 2021, Emmanuel Macron announced the launch of the “Prezode” initiative, which aims precisely to develop such prevention strategies at local levels and to connect them together, on a global scale. Today, it brings together 25 governments and 250 member institutions which together, with the WHO in particular, develop prevention strategies. This involves, for example, having tools that public policies can put in place, on the biosecurity of farms, for example.
Furthermore, we know that the level of virus circulation increases when we observe a loss of biodiversity. We must therefore look at ways of protecting biodiversity to limit the risk of its emergence in humans, but also develop monitoring networks and train local actors throughout the world.
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