Global spread of H5N1 avian flu virus puts scientists on guard

The H5N1 avian flu virus, which has killed more than half of the nearly 900 people it has infected since 2003, continues its global spread and is spreading in North American birds this spring after already taking root in Asia, Middle East, Africa and Europe.

At this time “the risk assessment for the general population is considered low,” the US Centers for Disease Control and Prevention (CDC) reported in a statement issued on Thursday, April 28, after the first case of human infection in the country.

The H5N1 virus causes outbreaks in farmed ocells in Europe and North America, which have been infected by wild ocells.

Charlie Neibergall/AP

The pathogen has not acquired the ability to spread efficiently between people It has killed more than half the people it has infected since 2003

But this type of virus “is of concern not only for birds but also for people because they pose a potential pandemic risk,” Australian infectologists Michelle Wille and Alan G. Barr warned on Friday 29 in the journal Science . “The ongoing 2021-2022 wave of bird flu is unprecedented in its speed of spread and extremely high frequency of outbreaks in wild and poultry birds, and is a continuing potential threat to people.”

For now, the chance of the H5N1 virus starting a human flu pandemic is considered low. “This virus has been causing problems in birds, with occasional infections in humans, for more than 20 years,” recalls Adolfo García-Sastre, director of the Institute for Global Health and Emerging Pathogens at Mount Sinai Hospital in New York. “If it has not yet been able to start a pandemic, it is very unlikely that it will be in the coming years. But flu pandemics, like the lottery, are unpredictable.”

H5N1 viruses

H5N1 viruses

In anticipation that the situation could worsen, the CDC has reported that “it is taking routine preparedness and prevention measures, including a candidate vaccine virus that could be used to make vaccines for people.”

For an influenza pandemic to occur, an influenza virus to which the human species has not yet been exposed must acquire the ability to efficiently transmit from person to person. This happened in 1919, 1957, 1968 and 2009, and it is considered inevitable that sooner or later it will happen again.

It has killed more than half the people it has infected since 2003

But H5N1 does not seem like a good candidate because “it is extremely unlikely that a virus with this difficulty of transmission between people could become a pandemic virus,” says Joaquim Segalés, a specialist in animal diseases at the Universitat Autònoma (UAB) and the Institute of Research and Agrifood Technology (IRTA). Segalés recalls that “H5N1 has the ability to infect people if there is a very direct exposure to infected birds, with a significant viral load and without protection measures.”

To prevent infection, the CDC recommends avoiding contact with poultry that appear sick or dead and avoiding touching surfaces with bird feces, both domestic and wild. If you have to handle birds, it is recommended to use gloves, mask and goggles and wash your hands well after contact with animals. Eating properly handled and cooked poultry products poses no risk, reports the CDC.

“If it has not yet been able to start a pandemic, it is very unlikely that it will be in the coming years. But flu pandemics are unpredictable.”

Adolfo García-Sastre, virologist at Mount Sinai Hospital in New York

Adolfo Garcia-SastreMount Sinai Hospital

In Spain, no case of influenza in people caused by H5N1 or any other subtype of avian influenza virus has been reported so far.

Although H5N1 is not very competent to infect people, it does seem to have increased its ability to infect birds in recent years. “The H5N1 virus clearly has a competitive advantage over [otros] avian influenza virus that predominated between 2014 and 2021”, they write in Science Michelle Wille, from the University of Sydney, and Ian Barr, from Melbourne.

bird flu

Caring for a quarantined eagle at the end of March at The Raptor Center in the USA.


Migrations of waterfowl, which have the virus but do not get sick from it, have spread H5N1

It has spread with the migration of waterfowl, which are its natural reservoirs and do not usually get sick from the virus, and has wreaked havoc on wild and poultry birds on all continents except Antarctica, Australia and South America.

“There are more than a hundred species of birds susceptible to infection by highly pathogenic influenza viruses. However, not all birds are equally susceptible to getting sick”, explains Joaquim Segalés. Farm birds such as chickens and turkeys, which die in almost 100% of cases, are among the most vulnerable, which has a high cost for the poultry sector. Deaths in wild birds, such as the 48 bald eagles found dead in the US as of April 26, allegedly after hunting infected ducks and geese, have serious effects on ecosystems.

In chickens and turkeys, H5N1 infection is fatal in almost 100% of cases

“Being a notifiable disease, each time an introduction by wild birds is detected, specific measures are taken, with birds from infected farms being culled, so it has no chance of becoming an endemic disease of poultry. corral”, says Segalés.

Regarding the possibility that the H5N1 virus acquires a greater capacity to infect human cells and could cause a pandemic, the CDC reports that there are three signs that “could increase the risk to public health.” One is that notifications of infections in people who have had contact with birds will increase. Another is that cases of contagion between people were reported. Finally, it would be a cause for concern if mutations were detected in the H5N1 virus genome associated with a greater capacity for contagion between mammals. None of these signs have been observed so far.

H5N1 is “a low threat to humans at this time,” write Michelle Wille and Ian Barr in Science . But “any potential pandemic threat should be taken seriously.”

The CDC, for its part, reported on April 28 that it “will continue to monitor the situation closely.”

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