In recent years, a strain of highly pathogenic avian influenza, H5N1, has been devastating bird populations around the world. In the US alone, over 60 million agricultural birds have been affected, along with thousands of wild birds. So far, only a few cases have been detected in humans, and many experts think that for now, it is unlikely to spread to people in wide outbreaks. People still have to be directly infected by a bird, and cannot transmit the virus to other people. However, H5N1 is not the only type of bird flu. One subtype called H3N8 has been identified in poultry farms in China. Scientists have now found genetic changes that have been happening in this virus, which may increase the risk it poses to humans. The findings have been reported in Cell. The study authors are concerned that H3N8 could lead to an epidemic or pandemic, and that these viruses have to be closely monitored.
H3 flu viruses have been shown to infect dogs, cats, humans, horses, poultry, pigs, seals, and wild aquatic birds. H3N8 was detected in horses in North America in 1963, in North American waterbirds in 2002, and in dogs in 2006. It was isolated from a human patient for the first time in 2022; a four-year-old boy in China, whose family raised chickens at home, contracted the virus. It was determined that the child was infected directly by a bird, and the child could not spread the virus to another person. The patient recovered, as did another person in China who fell ill with H3N8 in 2022.
In April 2023, another individual in China was infected with H3N8, and died. This patient was a 56-year-old woman who had multiple underlying conditions, and was frequently exposed to wild birds. She also did not transmit the virus to any other people.
The virus was isolated from the patient who died, and researchers have carefully analyzed it. They also studied it in mouse and ferret models. This work revealed that several mutational changes have arisen in the H3N8 genome that can lead to more severe infections in both animal models, and which also made it transmissible between animals, through the air.
Right now, the virus has the potential to cause severe respiratory disease and potentially death in humans. While many animals in poultry flocks carry this virus, we still don't know a lot about how it could make the leap from infecting animals to infecting humans, and being transmissible from one human to another. However, the virus seems to have the potential to become a problem.
The avian H3N8 virus that was isolated from the patient, who had severe pneumonia, was able to efficiently replicate in both human bronchial and lung epithelial cells. It also had "extremely harmful" effects on laboratory animals and was passed on in respiratory droplets, noted study co-author Professor Kin-Chow Chang of the University of Nottingham.
"Importantly, we discovered that the virus had acquired human receptor binding preference and amino acid substitution PB2-E627K," added Chang. These changes are required for the virus to move through the air to another host.
Even if people have been vaccinated for the H3N2 flu that infects poeple, they seem to have no protection against this emerging H3N8 avian flus, and people may be vulnerable at the epidemic or pandemic level, said Chang.
"Acid resistance of influenza virus is also an important barrier for avian influenza virus to overcome to acquire the adaptability and transmissibility in new mammals or humans. The current novel H3N8 virus has not acquired the acid resistance yet. So, we should pay attention to the change on acid resistance of the novel H3N8 virus," added senior study author Professor Jinhua Liu of China Agricultural University.
Sources: University of Nottingham, Medical Express via AFP, Cell
