New research reveals that the bird flu viruses may be capable of replicating at temperatures higher than an average fever, a key bodily defense mechanism against severe infection. The international study led by the University of Cambridge and the University of Glasgow offers new details on how some viruses can be prevented from replicating by fever, while others may thrive.
“This study definitively highlights that a relatively small increase in body temperature can have a dramatic impact on disease outcome and that this protection can be mediated by temperature itself (as opposed to temperature stimulating immune responses),” Sam Wilson, a co-author of the study with Cambridge University, told Newsweek.
“Avian viruses are resistant to elevated temperature and this is likely one reason why avian viruses tend to cause more severe disease in humans,” Wilson added.
The new study follows the reported death of an “older adult” from Washington state, who contracted the bird flu virus known as H5N5 last week.
The Washington State Department of Health said in a statement that testing confirmed “The virus as H5N5, making this the first recorded infection with this variant in a person globally.” The department added that “The result was confirmed by the Center for Disease Control and Prevention (CDC).”
Despite the bird flu fatality, health officials noted that the risk to people remains low. They said they will continue to monitor any individuals who came into close contact with the person as a precaution to ensure that human-to-human spread has not occurred. Officials say there is no current evidence that shows the transmission of the virus between people, and that the person who died had a mixed flock of domestic birds in their backyard.
The report comes as the new research is raising concerns about people’s ability to fight the virus should it move toward human-to-human transmission.
Researchers found that unlike the human flu, where the virus thrives in the upper respiratory tract, the avian influenza virus thrives in the lower respiratory tract. The temperature in the lower respiratory tract is higher, with body temperature typically sitting at 98.6 Fahrenheit, while the upper respiratory tract typically stays at 91.4 Fahrenheit.
In birds, the avian virus often infects the gut, where temperatures can reach up to 107.6 Fahrenheit.
Scientists used influenza-infected mice to see how fever protects against certain viruses, but may not be as effective against bird flu. Researchers used a lab-modified human virus, known as PR8, which is not harmful to humans. Mice do not typically develop a fever in response to influenza A, so scientists duplicated a fever by raising the body temperatures of the mice. They discovered that while fever is effective at stopping human-origin influenza viruses from replicating, it is not particularly effective against avian flu viruses.
Researchers discovered that a 35.6 Fahrenheit increase in body temperature was enough to turn a severe human-origin flu virus from a severe infection into a mild one. However, avian flu viruses with a specific gene, PB1, which plays an essential role in virus replication, were able to withstand high temperatures and replicate, causing severe illness in the mice. This is particularly concerning, considering that human and bird flu viruses can “swap” genes when they simultaneously infect a host, such as swine.
“The ability of viruses to swap genes is a continued source of threat for emerging flu viruses. We’ve seen it happen before during previous pandemics, such as in 1957 and 1968, where a human virus swapped its PB1 genes with that from an avian strain. This may help explain why these pandemics caused serious illness in people,” Matt Turnbull, a co-author of the study with the University of Glasgow, said in a statement.
Researchers said that it is vital to monitor bird flu strains to safeguard against potential outbreaks, and that studies on “how resistant” viruses are to fever may help experts “identify more virulent strains.”
“Many species, such as pigs, can serve as intermediate species for influenza viruses en route from birds to humans,” Wilson told Newsweek. “Understanding the genetic signatures that make some influenza lineages cause more severe disease will help risk assess influenza viruses that circulate in animal reservoirs.”
Scientists are not pushing for any changes to current safety guidelines for the bird flu but the new research shows the importance of being vigilant against evolving threats from the disease.