Wednesday, May 25, 2016

Bat Flu Reassortment Possibilities : Revisited

# 11,400

Nearly 4 and 1/2 years ago (see A New Flu Comes Up To Bat)
we learned of A distinct lineage of influenza A virus from bats adding both HA 17 and a NA 10 genes to the growing list of influenza subtypes.

While bats are known to carry other zoonotic diseases (Rabies, Nipah, Marburg, etc), this was the first time that bats were linked to influenza A.

Eighteen months later, another new subtype (H18N11) was identified, again in South American Bats (see PLoS Pathogens: New World Bats Harbor Diverse Flu Strains), leading to speculation that these mammalian-adapted flu viruses might someday jump to other species – including man.

The CDC addressed the slim potential for these viruses posing a public health threat in their 2014 Bat Flu FAQ. 

How could bat flu viruses become capable of infecting and spreading among humans?
Because the internal genes of bat flu viruses are compatible with human flu viruses, it is possible that these viruses could exchange genetic information with human flu viruses through a process called “reassortment.”
Reassortment occurs when two or more flu viruses infect a single host cell, which allows the viruses to swap genetic information. Reassortment can sometimes lead to the emergence of new flu viruses capable of infecting humans.
However, the conditions needed for reassortment to occur between human flu viruses and bat flu viruses remain unknown. A different animal (such as pigs, horses, dogs or seals) would need to serve as a “bridge,” meaning that such an animal would need to be capable of being infected with both this new bat flu virus and human flu viruses for reassortment to occur. Since the discovery of bat flu, at least one study has been conducted to assess the possibility of reassortment events occurring between bat flu and other flu viruses (3).
So far, the results of these studies continue to indicate that bat flu viruses are very unlikely to reassort with other flu viruses to create new and potentially more infectious or dangerous viruses. In their current form bat flu viruses do not appear to pose a threat to human health.

Although unlikely, one plausible scenario would involve the reassortment of a bat and a mammalian virus in an intermediate host, such as a pig.

However, in 2014 we saw a report (see Nature Comms: A Chimeric Bat Flu Study) that reassuringly suggested that the H17N10 subtype may have a difficult time making the leap from chiropterans to humans.

Today we've a report published in the Journal of General Virology, where researchers in China forced the reassortment of the NS1 gene from H17N10 bat flu virus with a human H1N1 virus, proving reassortment is possible, although still very unlikely to happen in nature.   

The NS1 gene from bat-derived influenza-like virus H17N10 can be rescued in influenza A PR8 backbone

Authors: Xuejin Zhao1Boris Tefsen2Yan Li3Jianxun Qi4Guangwen Lu5Yi Shi6Jinghua Yan7Haixia Xiao8, George F. Gao9
Published Ahead of Print: 23 May, 2016 Journal of General Virology doi: 10.1099/jgv.0.000509

Published Online:

Influenza A viruses have the potential to cause pandemics due to the introduction of novel subtypes against which human hosts have little or no pre-existing immunity. Such viruses may result from reassortment between human and animal influenza viruses. Recently, new influenza-like viruses were identified in bats, raising the concern for a new reservoir of potential harmful influenza viruses that could form reassortants with categorized human influenza A viruses. 

However, up till now, no one was able to generate a recombinant reassortant virus containing a single functional gene or domain from H17N10 that could propagate.
Here, we demonstrate that a recombinant A/Puerto Rico/8/1934 (H1N1) virus with NS1 gene from H17N10 influenza-like virus can be successfully rescued. Furthermore, we used luciferase reporter assays and qRT-PCR to show that the NS1 protein from H17N10 inhibited Sendai virus (SeV) induced activation of IFN-β expression with an efficiency similar to NS1 from an H5N1 strain. Moreover, the crystal structure of the NS1 (H17N10) RBD is also similar to other NS1s. 

These results demonstrate that H17N10 influenza-like virus indeed contains functional genes that are compatible with categorized influenza A viruses.
Although the chance of this particular event occurring in nature seems negligible, further research is needed to address the possibility of the natural formation of reassortments.

Between the emergence of SARS and MERS (both linked to bats), Nipah, Ebola, and now the discovery of bat flu, the past couple of decades have turned out to be busy ones for Chiroptologists (scientists who study bats). 

These winged mammals are increasingly viewed as naturals hosts for, and potential vectors of, a number of newly recognized emerging pathogens.
All of which makes bats, and bat habitats, something to be avoided. To learn how you can stay safe around bats, the CDC offers the following advice.

Take Caution When Bats Are Near

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