Hundreds of wild sea lions in South America, a mink farm in Europe, and more than 58 million poultry Have they died.
All of these animals fell victim to the impact of avian influenza, a virus that circulates rapidly around the world, killing wild and domestic animals, altering ecologies and hampering food supplies.
Human health is inextricably linked with animal health, and these events are eerie reminders that a widespread outbreak in animals has potential consequences for humans.
In the US, the most recent wave of bird flu affected 17 mammals and more than 160 birds. Is he wider outbreak of H5N1 since it emerged as a concern in China in 1996.
The virus has been under close surveillance by scientists, even more so now that it has spread far and wide.
“This is the number one potential pandemic virus that everyone has been interested in for a long time,” said Richard Webby, an infectious disease researcher at St. Jude Children’s Research Hospital in Memphis, Tenn., and director of the Collaborating Center. of the World Health Organization. for Studies on the Ecology of Influenza in Animals and Birds.
Tedros Adhanom Ghebreyesus, Director General of the World Health Organization, said Wednesday that the spread of avian influenza to mammalian species should be closely monitoredand that risk to humans remained low for now.
“But we cannot assume that will continue to be the case, and we must prepare for any change in the status quo,” he said.
The large number of H5N1 in circulation has increased the risk of the virus spreading to other species, developing the ability to transmit between people, and becoming a pandemic.
But the virus has yet to unlock a complicated series of mutations, or genetic changes, that would allow it to spread more rapidly between people.
“It is a series of events, each of which is quite improbable. That is why I say that the risk to humans is currently low. The evolutionary barriers are high,” said Anice Lowen, a virologist and associate professor at Emory University School of Medicine. «It’s a numbers game. That’s one of the reasons why the scale of the current avian outbreak is worrying.»
Researchers are particularly concerned about this version of bird flu, H5N1, because most humans haven’t dealt with it before.
“We don’t have an immune response against H5. That is why the virus has pandemic potential,» Lowen said.
Scientists have also observed high rates of death and severe illness in chickens and mammals that have contracted H5N1, raising concerns that the virus could also cause severe illness in people.
The United States has counted only one human case of H5N1 in the United States: an inmate in a Colorado prison culling infected poultry on a farm. Previous infections to humans, mainly in people in Southeast Asia and North Africa who likely touched infected birds directly, had high fatality rates, although those numbers could be skewed by limited reports of mild cases.
H5N1 has long been a major pandemic concern. The version that has been circulating in ducks and other wild birds has evolved and adapted for efficient propagation.
As those animals travel, so does the virus, via droppings, saliva, and nasal secretions.
Wild birds are spreading viruses and infecting animals «in greater numbers and in a larger geographic footprint than ever before,» said Bryan Richards, coordinator of emerging diseases at the US Geological Survey’s National Center for Wildlife Health. Joined. More than 6,100 wild birds have tested positive for the virus in the US
Poultry farmed birds are likely to become infected by contact with wild bird feces or other secretions.
Scavengers such as bears, raccoons and foxes have also been infected, likely after eating a dead or diseased bird, Richards said. Marine mammals, including dolphins, have also tested positive.
Recently, more than 500 sea lions were found dead with H5N1 in Peru. It is not clear if the virus was spreading between these species or if the animals became infected through food.
The virus is ill-adapted to spread between people.
“The avian virus is not as good at sticking to human cells as it is in the airways of birds. They’re just not adapted to humans,” said Dr. Helen Chu, an infectious disease physician and influenza expert at UW Medicine in Seattle.
To effectively spread in humans, the virus would need to make several genetic changes. That process would probably take place in other mammals.
Webby and Lowen said there were two main processes that the virus could undertake to better bind to receptors on human respiratory cells.
The first would be for the virus to change rapidly through reorganization, an «evolutionary shortcut» in which an animal becomes infected with both an avian influenza virus and a human virus, Lowen said. During coinfection, the two segmented influenza viruses could exchange bits of genetic code and combine to create a chimeric virus.
That virus likely needs more replication to correct the mismatched genes and develop traits that allow it to thrive in humans.
«It would be very concerning to see rearrangements, but they probably couldn’t be transmitted in humans yet,» Lowen said. «Probably what would be needed is more evolution to correct the mismatches.»
Previous Avian Influenza Pandemics – which began in 1957 and 1968 – required further rearrangement and mutations before they could spread widely among humans, Webby said. Each of these pandemics killed around 1 million people worldwide and around 100,000 people in the US.
The second option is for the virus to mutate within a dense group of animals. Researchers became concerned after an apparent H5N1 outbreak at a mink farm in Spain.
“They are in little cages close together. There is a level of transmission efficiency,” Chu said of the mink.
studies over a decade ago showed that ferrets could detect H5N1 airborne mutations after serial infections.
In the recent mink farm outbreak, the virus likely spread from mink to mink, Webby said. Although it picked up a worrying mutation, it remained largely adapted for birds. The minks were euthanized.
“Luckily it was eradicated,” Webby said.
The virus faces major genetic hurdles, but the more it spreads in animals, the better chance it has of overcoming those barriers.
Lowen said governments should invest more in monitoring potential hosts that could help the virus jump to humans, consider measures such as vaccination to limit spread in poultry, and invest in science to help determine what changes Genetics could be worrisome for people.