A poultry shed in Florida. Photo:
Avian influenza viruses are more resistant to fever and therefore likely to cause more severe disease and pandemics in humans following spillover, claims a British modelling study.
Not without reason do many virologists worry about outbreaks of highly pathogenic avian influenza (HPAI), of which twenty have already been reported in the Netherlands this autumn. A modelling study by British virologists shows that avian influenza carrying a mutation in the PB1 polymerase protein has more severe consequences for mice, because the standard fever response does not attenuate such a variant. Probably because avian influenza variants are adapted to the higher body temperatures of 40 to 42 degrees Celsius found in birds (Science, 28 November).
The everyday fever response – a rise in body temperature of around 2 degrees – normally causes severe viral infections to follow a milder course. It is, however, difficult to study in humans whether elevated temperatures also have an inhibitory effect on avian influenza. In the present study, British researchers used PB1 proteins from avian influenza strains, incorporating a component of the viral polymerase known to enable viral replication at higher temperatures. This protein has also been identified in the pandemic influenza viruses of 1918, 1957 and 1968, and is associated with a more severe course of influenza.
Image accompanying the web article on this research from the Cambridge Institute of Therapeutic Immunology and Infectious Diseases. Source: University of Cambridge website.
The animal experiments used a modified influenza virus of human origin that is no longer pathogenic in humans but does cause severe symptoms in laboratory mice. It replicates poorly at 40 degrees Celsius, but two altered amino acids in the PB1 protein are sufficient to produce a mutant that replicates effectively at this temperature. Even under simulated fever conditions – achieved by raising the ambient temperature – mice infected with this mutant continued to suffer severe influenza symptoms, whereas control mice showed relatively mild symptoms. ‘Such fever-resistant replication may help explain why avian spillover viruses and pandemic influenza viruses with a PB1 of avian origin cause more severe disease in humans’, the researchers write.
Bionieuws approached several Dutch influenza experts for external comment, but unfortunately was unable to obtain responses before the newspaper’s deadline.
A fantasy drawing by seven-year-old Solanyi van Maanen Martens depicting chickens heading for freedom during the avian influenza outbreak in the Netherlands in 2003.
See also:
–Bird flu viruses are resistant to fever, making them a major threat to humans – website University of Cambridge & website University of Glasgow, 28 November 2025