Unlike with the more dangerous Asian lineage of H5Nx (H5N1/H5N6) viruses, all known human infections with the Eurasian HPAI H5 virus have been mild.
In early 2021 Russia announced 7 infections among poultry workers, which convinced the CDC To Add Zoonotic Avian A/H5N8 To Their IRAT List last May. Last December the ECDC/EFSA Raised the Zoonotic Risk Potential Of Avian H5Nx, following the detection of a human infection in the UK.
- In 2015, after the death of the first imported H5N1 case in Canada, we saw a study (see CJ ID & MM: Case Study Of A Neurotropic H5N1 Infection - Canada), where the authors wrote:
These reports suggest the H5N1 virus is becoming more neurologically virulent and adapting to mammals. Despite the trend in virulence, the mode of influenza virus transmission remains elusive to date. It is unclear how our patient acquired the H5N1 influenza virus because she did not have any known contact with animals or poultry.
- Similarly, in a Scientific Reports open access study on the genetics of the H5N1 clade 22.214.171.124c virus - Highly Pathogenic Avian Influenza A(H5N1) Virus Struck Migratory Birds in China in 2015 – the authors warned:
This suggests that the novel Sanmenxia Clade 126.96.36.199c-like H5N1 viruses possesses tropism for the nervous system in several mammal species, and could pose a significant threat to humans if these viruses develop the ability to bind human-type receptors more effectively.
Yesterday the Canadian Wildlife Health Cooperative announced the first known spillover of the Eurasian H5N1 virus into a non-human mammalian species (foxes) in North America, with similar neurological symptoms.The details are provided by a blog post yesterday on the Healthy Wildlife webpage by CAROLYN BLUSHKE
Working with our partners at the Canadian Food Inspection Agency (CFIA) and the Animal Health Laboratory, the CWHC ON/NU diagnosed influenza A (H5N1) in 2 wild fox kits in Ontario, on May 2, 2022. These cases represent the first detections of highly pathogenic avian influenza virus (HPAIV) H5N1 A/goose/Guangdong/1996 (Gs/GD) lineage in wild mammals in Ontario, Canada and in the Americas.
The fox kits were found together in St. Marys, Ontario and submitted from a wildlife rehabilitation centre. One of the kits was found dead and the other was exhibiting severe neurological signs (including seizures) and died shortly after admission to a wildlife rehabilitation centre. Based on clinical signs, post-mortem/microscopic examination, and the detection of influenza A (H5N1) virus in brain tissue, it is likely that influenza A (H5N1) virus was the cause of mortality for these foxes.
The type of exposure (inhalation vs. ingestion) - and the infectious dose - likely makes a difference, as does the host species. What happens with a fox that likely consumed raw, heavily infected meat, may not tell us very much about someone who is exposed to infected poultry.
Despite two decades of concern, and hundreds of human infections (mostly from the Asian lineage), H5Nx has failed to adapt well enough to humans to pose a serious global health threat. And in truth, it may never happen (or it could happen tomorrow).
For now, the evidence suggests that the Eurasian HPAI H5 viruses circulating in Europe and North America pose a very low risk to human health.