While public health officials say the risk to humans is still very low, they are concerned about mutations after a number of mammals have been found to have contracted the bird flu virus.
According to the World Health Organization (WHO), zoonotic influenza infections in humans may be asymptomatic or may cause disease, from conjunctivitis or mild, flu-like symptoms to severe, acute respiratory disease or even death, depending on factors related to the virus causing infection and the infected host. Rarely, gastrointestinal or neurological symptoms have been reported. WHO assesses the risk to the human population to be low, however recent studies show that the virus has shown potential mutation among cases in mammals.
In the U.K., the Animal and Plant Health Agency (APHA) has tested 20 mammals, and found eight were positive for highly pathogenic avian influenza (HPAI) H5N1. It is likely that these mammals fed on very sick or dead birds but there is also concern that the virus is spreading between mammals following additional data from around the world.
APHA says that four of the eight positive cases have genome sequences available and all show the presence of a mutation which is associated with potential advantages for mammalian infection. Together with supporting international data, the results are suggestive of sporadic mammalian spillover events. Last year for example, infections were found in about a dozen species in the United States, including raccoons, foxes, seals and grizzly bears. An outbreak of avian influenza on a mink farm in Spain provides the strongest evidence so far that the H5N1 strain of flu can spread from one infected mammal to another, and Hualan Chen, a virologist at the Harbin Veterinary Research Institute in China said the spread of the virus between mammals imposes a higher risk to public health.
APHA is working with the UK Health Security Agency (UKHSA) and the Department for Environment, Food and Rural Affairs to investigate the risk to human health of avian influenza in England. A recent UKHSA report noted that from October 1, 2022 to December 15, 2022, health protection systems recorded 2,085 human exposure episodes (where a person was directly exposed to an infected bird). There is likely to be substantial under ascertainment. Based on the 29% of incidents for which there is data, personal protective equipment was used in 27.3% of exposures, and antiviral prophylaxis in 15.9% of exposures. Symptoms were reported following 31 (4.3%) exposures, with 24 symptomatic swabs being carried out (77.4% of those eligible).
Last year, a man in Colorado was diagnosed with avian influenza. Media reports at the time indicated he was involved with culling poultry and infected by a sick bird. According to the Centers for Disease Control and Prevention (CDC), he had mild symptoms, was isolated, and recovered. Nichola Hill, an assistant professor of biology at the University of Massachusetts said the fact that his symptoms were mild is concerning because it makes the virus harder to detect and track, as infected individuals may ignore mild symptoms and not seek treatment—much like COVID-19.
And last month, WHO was notified of a human infection caused by an avian influenza virus. The case, a nine-year-old girl, living in a rural area in the province of Bolívar, Ecuador, was in contact with backyard poultry, which was acquired a week before the onset of her symptoms. As of January 18, WHO reported that she remained hospitalized, in isolation, and treated with antivirals.
CDC says that human infections with bird flu viruses have occurred most often after unprotected contact with infected birds or surfaces contaminated with bird flu viruses. However, it notes that some infections have been identified where direct contact with infected birds or their environment was not known to have occurred.
“The spread of bird flu viruses from one infected person to a close contact is very rare and when it has happened, it has only spread to a few people,” CDC says. “However, because of the possibility that bird flu viruses could change and gain the ability to spread easily between people, monitoring for human infection and person-to-person spread is extremely important for public health.”
Currently there are no approved vaccines for preventing avian influenza in humans. However, candidate vaccines have been developed for pandemic preparedness purposes.
Jonathan Runstadler, professor and chair of the Department of Infectious Disease & Global Health at Cummings School of Veterinary Medicine, believes this particular outbreak will not be going away any time soon. It differs from earlier outbreaks in that this time around the whole H5N1 virus, not just a part of it, is circulating, and it is doing so faster than previous outbreaks. “There’s reason to expect this virus is here to stay, and it’s not going to disappear,” said Runstadler.
Prof Ian Brown, APHA’s director of scientific services, recently shared his concerns with the BBC. “The virus is absolutely on the march. And it’s almost remarkable – it’s a single strain,” he said, adding that he was “acutely aware of the risks” of avian flu becoming a pandemic like COVID-19.
