A recent study conducted by the University of Cambridge has identified a concerning characteristic of bird flu viruses: their apparent resistance to fever, one of the body's primary defenses against viral infections. This discovery has heightened concerns about the potential for a bird flu pandemic.
Humans typically fend off viruses with fever, which elevates the body's temperature to slow down viral replication, aiding the immune system in combating infections. The majority of human flu viruses are hindered by this process. However, the Cambridge researchers have found that bird flu viruses can thrive at higher temperatures, akin to those found in birds' lower respiratory tracts, ranging from 104 to 108°F. This adaptation makes them less affected by the fever response in humans.
"This is crucial for surveillance and pandemic preparedness," said Dr. Sam Wilson, highlighting the importance of understanding bird flu's resistance to fever.
The research team conducted experiments using a lab-grown PR8 flu virus in mice, modifying it to mimic the behavior of either human or bird flu. When the mice were subjected to temperatures simulating a human fever of 106°F, the human-adapted virus struggled to replicate. Conversely, the bird flu-adapted virus continued to multiply, resulting in severe illness in the mice.
Dr. Sam Wilson, a molecular virologist at Cambridge, commented on the infrequency of human bird flu infections, yet highlighted the gravity of cases that do occur. Wilson pointed out the alarmingly high mortality rates historically associated with H5N1 bird flu infections, exceeding 40 percent.
Understanding the mechanisms behind the severe illness caused by bird flu is vital for pandemic preparedness and surveillance, according to Wilson. His concerns are echoed by global health officials in light of a recent bird flu-related death in Washington state, caused by a novel strain of the virus, and French officials' warnings that a bird flu pandemic could surpass the lethality of COVID-19.
In the United States, there have been 71 reported human bird flu infections since January 2022, predominantly of the H5N1 variety. Most cases were linked to contacts with infected poultry or dairy cows. The research further emphasizes the severe disease developed by mice infected with the bird flu-like virus even at elevated temperatures resembling human fever. In contrast, mice with the human-adapted virus did not experience severe illness.
Dr. Matt Turnbull, a virologist at the University of Glasgow and lead author of the study, stressed the importance of monitoring bird flu strains to anticipate potential outbreaks. Turnbull suggested that testing for resistance to fever could aid in identifying more aggressive strains, thereby preventing human spillover.
The risk of bird flu spreading efficiently among humans is currently deemed low by the CDC, but ongoing vigilance is crucial due to the threat of mutations that could lead to a pandemic. Since 2022, bird flu has impacted over 174 million wild and domestic birds in the U.S., as well as over 1,000 dairy herds. This year alone, 7 million farmed birds have been infected, including 1.3 million turkeys.
