A recently published study shows that the Nile fruit bat influenza A virus subtype H9N2 replicates well in ferrets and is well transmitted between them. It also efficiently infects human lung explant cultures and is able to evade antiviral inhibition by the human MxA protein in the mouse model.
The dynamic infection pattern of influenza A virus subtype H5N1 ("avian flu") has developed into an almost global pancytosis in wild birds. Currently, the steadily increasing number of infected cows in the USA is a cause for concern. However, influenza A viruses can pose a health risk not only to animals but also to humans in certain cases. New human cases, including the H9N2 subtype, continue to be confirmed, including a recent case with severe symptoms in Vietnam. A group of international scientists therefore took a closer look at another influenza A virus of subtype H9N2 from a fruit bat (Rousettus aegyptiacus). They found that this virus has a number of characteristics that could make it easier to infect humans and spread in the population. However, it is important to note that there is no evidence of species jumping for this bat virus and no known human cases.
In 2017, the influenza A virus of subtype H9N2 was detected and successfully isolated in Nile Flying Dogs from Egypt, Africa. In addition, the virus was also detected in Nile Flying Dogs from South Africa in early 2023, indicating a strong spread of this bat H9N2 across the African continent. As very little was known about this virus, FLI researchers teamed up with global collaborators to investigate its zoonotic potential. They found that bat H9N2 is capable of replicating efficiently in ferrets and can be transmitted to contact animals. In addition, turkey, chicks could be infected with the virus, allowing it to cross the species barrier to certain birds.
In addition, the H9N2 bat showed a surprising resistance to the highly antiviral MxA protein. A property previously only known from pandemic human influenza viruses. Finally, it was shown to replicate efficiently in human lung explants. Based on the finding that conventional influenza vaccines do not induce cross-reactive antibodies against the bat H9N2 N2 protein, further studies are needed to determine its pre-pandemic potential, including analyses in humans and animals in contact with fruit bats in Africa.
The scientists stress that extensive surveillance and diagnosis of bat H9N2 is needed to identify new virus isolates, assess the current spread of the virus and detect potential transmission to other animal species or humans. At the same time, the researchers stress that these specific and important results could not have been achieved without the use of animal experiments.
FLI publication:
Halwe, N.J., Hamberger, L., Sehl-Ewert, J. et al. Bat-borne H9N2 influenza virus evades MxA restriction and exhibits efficient replication and transmission in ferrets. Nat Commun 15, 3450 (2024). DOI: 10.1038/s41467-024-47455-6
Publication on bat H9N2 without FLI involvement:
El-Shesheny, R., Franks, J., Kandeil, A. et al. Cross-species spill-over potential of the H9N2 bat influenza A virus. Nat Commun 15, 3449 (2024). DOI: 10.1038/s41467-024-47635-4
