Thursday, February 23, 2023

ASM Journal: Characterization of an H7N9 Influenza Virus Isolated from Camels in Inner Mongolia, China


Photo Credit Wikipedia 


Between 2013 and mid-2017 a new, and unexpected, avian flu threat emerged in China; (LPAI) H7N9 virus.  As a low path avian virus, it could spread asymptomatically in poultry, but it could produce severe (even fatal) illness in humans. 

Across 5 distinct waves, China reported a total of 1568 lab-confirmed human infections, including 616 fatal cases (CFR: 39%). Several estimates, however, suggest the real number of infections was far higher.
H7N9 Epidemic Waves - June 14th 2017 - Credit FAO

Fearing that H7N9 was on the verge of sparking a pandemic, in 2017 China unveiled a massive, nationwide, H5+H7 poultry vaccination campaign  which produced a remarkable drop in human infections, poultry outbreaks and virus detection from routine surveillance (see OFID: Avian H5, H7 & H9 Contamination Before & After China's Massive Poultry Vaccination Campaign).

While the number of human infections dropped precipitously following the vaccine campaign, the virus never truly went away.

Between three years of COVID lockdowns, and the rise of H5Nx viruses, H7N9 has become a largely forgotten avian flu threat. But as today's report illustrates, the virus continues to evolve, and make worrisome inroads in to non-avian hosts. 

I've only reproduced the Abstract, so follow the link to read it in its entirety.  I'll have a brief postscript when you return. 

Characterization of an H7N9 Influenza Virus Isolated from Camels in Inner Mongolia, China

Authors: Yuncong Yin, Yuan Liu, Juan Fen, Kaituo Liu, Tao Qin, Sujuan Chen, Daxin Peng, Xiufan LiuAUTHORS INFO & AFFILIATIONS



The H7N9 subtype of influenza virus can infect birds and humans, causing great losses in the poultry industry and threatening public health worldwide. However, H7N9 infection in other mammals has not been reported yet. 

In the present study, one H7N9 subtype influenza virus, A/camel/Inner Mongolia/XL/2020 (XL), was isolated from the nasal swabs of camels in Inner Mongolia, China, in 2020. Sequence analyses revealed that the hemagglutinin cleavage site of the XL virus was ELPKGR/GLF, which is a low-pathogenicity molecular characteristic.

The XL virus had similar mammalian adaptations to human-originated H7N9 viruses, such as the polymerase basic protein 2 (PB2) Glu-to-Lys mutation at position 627 (E627K) mutation, but differed from avian-originated H7N9 viruses. The XL virus showed a higher SA-α2,6-Gal receptor-binding affinity and better mammalian cell replication than the avian H7N9 virus. 

Moreover, the XL virus had weak pathogenicity in chickens, with an intravenous pathogenicity index of 0.01, and intermediate virulence in mice, with a median lethal dose of 4.8. The XL virus replicated well and caused clear infiltration of inflammatory cells and increased inflammatory cytokines in the lungs of mice. Our data constitute the first evidence that the low-pathogenicity H7N9 influenza virus can infect camels and therefore poses a high risk to public health.


H5 subtype avian influenza viruses can cause serious diseases in poultry and wild birds. On rare occasions, viruses can cause cross-species transmission to mammalian species, including humans, pigs, horses, canines, seals, and minks. The H7N9 subtype of the influenza virus can also infect both birds and humans. However, viral infection in other mammalian species has not been reported yet. In this study, we found that the H7N9 virus could infect camels. 

Notably, the H7N9 virus from camels had mammalian adaption molecular markers, including altered receptor-binding activity on the hemagglutinin protein and an E627K mutation on the polymerase basic protein 2 protein. Our findings indicated that the potential risk of camel-origin H7N9 virus to public health is of great concern.

Camels are somewhat famously known as (likely) intermediate hosts for the MERS-CoV virus, and exposure to camels and camel products continues to provide opportunities for the virus to spillover into humans in the middle east. 

Camels (both bactrian and dromedary) have also been shown to be susceptible to a variety of influenza viruses, which we've discussed previously in :

Two New Influenza D Studies To Ponder

This was also the topic of a study, published in early 2020, that documented seasonal influenza (H1N1 and H3N2) in Nigerian Camels. 

Emerg Infect Dis. 2020 Jan; 26(1): 173–176.

Influenza A Virus Infections in Dromedary Camels, Nigeria and Ethiopia, 2015–2017

While H5N1 is currently at the top of our pandemic worry list, nature is an excellent multitasker, and we could easily be blindsided by something that comes from out of left field.