Notably in the first (severe) case, the family dog and cat both tested positive for H3N8, and a full-length HA sequencing revealed the HA to be identical to the boy's.
Preprint: Human infection With a Novel Reassortment Avian Influenza A H3N8 Virus: An Epidemiological Investigation Study
Our knowledge of how the virus is evolving and spreading in the wild is fairly limited. This week, however, we get a detailed look at the evolution of H3N8 in Eastern China from 2017 to 2021.
This is a lengthy, and very detailed report, that provides a lot of insight on the prevalence of other avian flu viruses in Eastern China as well (see graphic below).
I've only posted the Abstract, and some excerpts from the discussion. Follow the link to read the open-access report in its entirety. I'll have a brief postscript after the break.
Article: 2184178 | Received 11 Sep 2022, Accepted 20 Feb 2023,Published online:13 Mar 2023
The continued evolution and emergence of novel influenza viruses in wild and domestic animals poses an increasing public health risk. Two human cases of H3N8 avian influenza virus infection in China in 2022 have caused public concern regarding the risk of transmission between birds and humans. However, the prevalence of H3N8 avian influenza viruses in their natural reservoirs and their biological characteristics are largely unknown.
To elucidate the potential threat of H3N8 viruses, we analyzed five years of surveillance data obtained from an important wetland region in eastern China and evaluated the evolutionary and biological characteristics of 21 H3N8 viruses isolated from 15,899 migratory bird samples between 2017 and 2021.
Genetic and phylogenetic analyses showed that the H3N8 viruses circulating in migratory birds and ducks have evolved into different branches and have undergone complicated reassortment with viruses in waterfowl. The 21 viruses belonged to 12 genotypes, and some strains induced body weight loss and pneumonia in mice. All the tested H3N8 viruses preferentially bind to avian-type receptors, although they have acquired the ability to bind human-type receptors.
Infection studies in ducks, chickens and pigeons demonstrated that the currently circulating H3N8 viruses in migratory birds have a high possibility of infecting domestic waterfowl and a low possibility of infecting chickens and pigeons.
Our findings imply that circulating H3N8 viruses in migratory birds continue to evolve and pose a high infection risk in domestic ducks. These results further emphasize the importance of avian influenza surveillance at the wild bird and poultry interface.
In recent decades, emerging novel animal influenza viruses and other zoonoses have posed major challenges to the global commercial poultry industry and public health [Citation5, Citation43, Citation44]. However, H3N8 avian influenza viruses have been ignored due to their low prevalence in chickens and the low risk to public health, although it has become one of the predominant strains in migratory waterfowl and domestic ducks.
Recent human infections with H3N8 viruses in China have promoted interest in and concern about the evolution and cross-species transmission risk of these viruses. In this study, we performed a detailed analysis of the global distribution of H3N8 viruses in different hosts according to deposited sequence data and our surveillance results in eastern China between 2017 and 2021. The summarized results indicated that migratory ducks are the primary natural reservoirs of H3N8 viruses. Here, a total of 162 viruses belonging to 28 subtypes were identified and isolated from 15,899 wild bird samples, which suggested that wild birds are natural reservoirs of different subtypes of avian influenza viruses and play a key role in the maintenance and evolution of such viruses.
H3N8 viruses have been detected in at least 64 kinds of wild birds and have evolved into several phylogenetic lineages, whereas only a few strains were detected in chickens in recent years. The H3N8 viruses analyzed in this study shared similar sequence identities and clustered into the same lineages with some strains isolated from Europe, North America and Africa, suggesting that H3N8 viruses can be transmitted globally with the migration of their natural reservoirs.
We also found that these H3N8 viruses have undergone complicated reassortment with circulating H5N3, H7N4, H9N2, H10N4 and H10N8-like viruses isolated from Yellow River Delta wetlands [Citation21, Citation33, Citation34]. Of note, all the H3N8 viruses detected from chicken and humans in China in 2022 share HA and NA surface genes similar to those of duck- and wild bird-origin strains but bear an internal gene constellation from chicken H9N2 viruses [Citation29, Citation31].
The predominantly prevalent H9N2 viruses have been proven to be ideal internal gene donors for the emerged reassortants, including H7N9, H10N3, and H10N8 viruses [Citation8, Citation13, Citation45, Citation46]. The complicated epidemiology and ecology of avian influenza viruses at the interface of waterfowl and terrestrial birds could have facilitated the emergence of novel H3N8 reassortants in chickens. Therefore, monitoring AIVs in wild and domestic waterfowl and controlling H9N2 viruses in domestic birds will contribute to early warning and reduction in the occurrence of natural avian influenza reassortants.
In summary, we described the distribution of H3N8 viruses and characterized the genetic and biological properties of H3N8 viruses isolated from wild birds in a wetland in eastern China. Our findings emphasize that active surveillance in migratory birds and domestic ducks will contribute to early detection of the emergence and evolution of AIVs in waterfowl and potential threats to the commercial poultry industry and human health.
While the number of H3N8 spillover events pale when compared to H5N1, H5N6, or H7N9, it is an important reminder that nature's laboratory is open 24/7, and it has a wide range of experiments going all of the time.