February 16, 2023 – A highly contagious strain of bird flu – often called H5N1 – is spreading world wide, devastating birds in each private homes and industrial operations. Although this virus primarily affects birds, increasing reports of mammals infected with the virus have some experts fearful. The biggest concern, they are saying, is that H5N1 is continuous to spread and reproduce in several species, potentially giving the virus more opportunities to develop mutations that might help it infect humans more easily.
“The sheer number of viruses alone makes them more likely to infect people or [other] “The more mammals that are infected, the greater the chance that this rare event will occur,” says Dr. Richard Webby, director of the World Health Organization-affiliated Center for Studies on the Ecology of Influenza in Animals and Birds at St. Jude Children's Hospital in Memphis.
Since May 2022, the U.S. Department of Agriculture has determined 121 mammals infected with the H5N1 virus, including red foxes, skunks, bears and even seals. In October 2022, an outbreak on a mink farm in Spain led to the culling of over 51,000 animalsand earlier this month Peru confirms 585 sea lions have died from the virus in coastal conservation areas. Although H5N1 infections have been detected in mammals over the past 25 years, “we're definitely seeing an increase in reported cases in the past 12 months,” says Webby.
The World Health Organization has stated that the risk to humans remains low, “but we cannot assume that it will remain so and we must prepare for any change in the status quo,” said WHO Director-General Tedros Adhanom Ghebreyesus, PhD, at a News overview this month.
Infections in humans remain rare
H5N1 infections in humans are rare. They normally occur when someone has unprotected, direct contact with H5N1-infected birds or surfaces contaminated with the virus. Since 1997, there have been about 870 cases in humans Cases have been reported to the WHO, with about half of them dying from the infection. Even if someone is infected with the virus, it’s even rarer for the infection to be passed on to a different person.
“The H5N1 viruses currently circulating in wild birds and causing poultry disease are well adapted to spread among birds,” said Tim Uyeki, MD, chief medical officer of the Office of the Director of the CDC’s Influenza Division, in a Online questions and answers. “However, these H5N1 avian influenza viruses do not have the ability to easily bind to receptors in the human upper respiratory tract or to be transmissible from person to person.”
Despite record numbers of infected wild birds and poultry, infections in humans less frequently in recent years. Since the start of this century, it has not been unusual for at the least 30 to 40 cases of H5N1 to be registered in humans annually. Since 2021, fewer than 10 infections have been reported worldwide, based on the CDC.
Further distribution in mammals
H5N1 infections in wild mammals will not be unusual, but also they are rare. Most of those cases probably occur when an animal eats an infected bird and is exposed to the virus. As with humans, these infections are sporadic. But a Report from last month about an outbreak at a mink farm in Spain raised concerns amongst experts as researchers suspected the virus can have been spread by one mink infecting others. Minks are related to ferrets, which scientists use as animal models to check flu transmission.
“If we see something that is transmissible in mink, it's not far-fetched to think, 'Maybe it's transmissible in ferrets,'” Webby says. “We would certainly use transmission in ferrets as a warning signal about the danger to humans.”
But up to now there isn’t any evidence that the virus has developed the power to contaminate people more easily, says Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center in Nashville.
“In fact, it is reassuring that at the mink farm in Spain, all the people who work on the farm – and who had very close contact with the minks – were tested and the result was negative,” he says. The minks were also confined in very tight cages – which could have facilitated the spread of the virus, he notes.
Recent reports of infections in sea lions have sparked speculation online concerning the possible spread of the virus amongst these animals. In fact, nonetheless, these marine mammals may have been involved with birds infected with H5N1.
What is evident is that the virus is widespread and is appearing in increasingly more animals, says Dr. Jennifer Nuzzo, director of the pandemic center at Brown University School of Public Health in Providence, Rhode Island. Why that is so is less obvious.
“Does that mean that [H5N1] has achieved a certain level of fitness relative to mammals? What does that mean for its potential to infect humans? We just don't know,” she says.
Will bird flu be the next pandemic?
Unfortunately, it is impossible to predict which type of virus will cause the next pandemic, but the WHO's global influenza surveillance and response system is already working hard to monitor influenza viruses around the world, says Schaffner.
“It's like a radar system that tries to detect the enemy as early as possible,” he says. The network tracks infections not only in humans, but also in birds and other animals.
In case bird flu becomes a real threat to the population, the United States already has a stockpile of bird flu vaccines.
“When we need them, they can be updated to the latest strain and production can begin immediately,” says Schaffner.
Although experts agree that the danger to the general public from H5N1 is low, people should avoid contact with sick or dead wild birds, poultry and wildlife. Do not eat raw or undercooked poultry, eggs or other poultry products. Eating cooked poultry, poultry products and eggs is protected. For more protective measures, see the CDC website.