Frontiers in Microbiology: A Novel Reasortant H7N6 Is Transmissible in Guinea Pigs via Respiratory Droplets

#13,863


For a full decade after it re-emerged in 2003, the Asian Highly Pathogenic H5N1 virus reigned as the top bird flu pandemic threat around the world.  Other - mostly H7 - avian viruses had shown a limited ability to infect humans, but produced generally mild symptoms (see A Brief History Of H7 Avian Flu Infections).

Our perception of H7 avian viruses changed in the spring of 2013, however, when a novel, low pathogenic H7N9 virus emerged in Eastern China. While it did not sicken poultry, it could jump to humans and cause a severe - often fatal - respiratory infection.

Since 2013, H7N9 has produced 1,567 confirmed cases and 615 deaths (cite), although the general consensus is that many more cases have gone unreported.

Within a year, two more novel flu HPAI viruses (H5N6 and H10N8) would emerge in the same region - and while human infections were less common than from H7N9 - both produced high mortality (30%+) among identified cases.

H10N8 appears to have been a flash in the pan, producing only 3 known human infections within the space of a few months. It could conceivable return someday, and pick up where it halted in 2014.

H5N6 has spread farther and has produced at least 24 human infections (see map below), more than half of which have been fatal.

After a decade of relative stability among avian flu viruses, starting in 2013, we've seen an explosion in new, reassorted avian viruses.

At roughly the same time, and new and highly virulent (in poultry and wild birds) H5N8 virus emerged, and began its world tour, causing record epizootics in North America (2014-2015) and Europe (2016-2017) but without infecting humans.

Along the way, this new H5 virus reassorted into new versions of H5N1, H5N2, H5N3, H5N5, and H5N9 (see 2017 ESA Report).  None have shown the ability to infect humans, but all have a profound effect on poultry.

We've seen similar reassortants emerge from the H7 viruses in China, including the report from exactly one year ago today (Jiangsu China Reports 1st Novel H7N4 Human Infection).

The upshot to all of this is that as new flu viruses emerge, they appear to have a snowball effect, providing more interchangeable parts, that enable the building of even more reassortant viruses.

Today we've a study, published in Frontiers in Microbiology, that examines a novel LPAI H7N6 virus detected in Hubei Province in 2017 - which appears to be a reassortment of H7N9 and H5N6 - and finds that it already has significant mammalian adaptations. 

• This novel H7N6 binds equally well to avian-like and human-like receptors
• It is virulent in mice without prior adaptation
• It is transmissible via direct contact and the airborne route in guinea pigs
  

All qualities we don't care to see in novel viruses.  This is a lengthy, detailed, open-access report.  I've only excerpted a few passages, so follow the link to read it in its entirety.

Published online 2019 Jan 22.

doi: 10.3389/fmicb.2019.00018
PMCID: PMC6349713
PMID: 30723462

A Novel Reassortant Avian H7N6 Influenza Virus Is Transmissible in Guinea Pigs via Respiratory Droplets

Zongzheng Zhao,1,2,† Lina Liu,1,† Zhendong Guo,2 Chunmao Zhang,2 Zhongyi Wang,2 Guoyuan Wen,1 Wenting Zhang,1 Yu Shang,1 Tengfei Zhang,1 Zuwu Jiao,1 Ligong Chen,3 Cheng Zhang,3 Huan Cui,3 Meilin Jin,4 Chengyu Wang,2,* Qingping Luo,1,* and Huabin Shao1,*
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Abstract

Since 2013, H7N9 and H5N6 avian influenza viruses (AIVs) have caused sporadic human infections and deaths and continued to circulate in the poultry industry. Since 2014, H7N6 viruses which might be reassortants of H7N9 and H5N6 viruses, have been isolated in China. However, the biological properties of H7N6 viruses are unknown.

Here, we characterize the receptor binding preference, pathogenicity and transmissibility of a H7N6 virus A/chicken/Hubei/00095/2017(H7N6) (abbreviated HB95), and a closely related H7N9 virus, A/chicken/Hubei/00093/2017(H7N9) (abbreviated HB93), which were isolated from poultry in Hubei Province, China, in 2017. 

Phylogenetic analyses demonstrated that the hemagglutinin (HA) gene of HB95 is closely related to those of HB93 and human-origin H7N9 viruses, and that the neuraminidase (NA) gene of HB95 shared the highest nucleotide similarity with those of H5N6 viruses. 

HB95 and HB93 had binding affinity for human-like α2, 6-linked sialic acid receptors and were virulent in mice without prior adaptation. In addition, in guinea pig model, HB93 was transmissible by direct contact, but HB95 was transmissible via respiratory droplets. 

These results revealed the potential threat to public health posed by H7N6 influenza viruses and emphasized the need for continued surveillance of the circulation of this subtype in poultry.

(SNIP)

In summary, a reassortant H7N6 virus was isolated; this virus exhibited comparable binding affinity for both avian-like and human-like receptors, and displayed efficient airborne transmission in the guinea pig model. Chickens may have played an important role in the generation of the novel reassortant H7N6 virus. Our study provided insight into H7N6 viruses in chickens in China.

Notably, low pathogenic H7N6 viruses can mutate to high pathogenicity subtypes during circulation in domestic chicken, thus posing an increased threat to human health. Therefore, constant surveillance of H7N6 viruses highly recommended to prevent a possible pandemic.

        (Continue . . . .)


A reminder that while we enjoy this recent respite from avian flu, nature's laboratory is open 24/7, and evolution never sleeps.