Monday, August 12, 2019

Nature: Semiaquatic Mammals As Intermediate Hosts For Avian Influenza


Yesterday, in IJID: Animal Influenza Virus Infections in Humans - A Commentary, we looked at a review/opinion piece that pegged swine as the most likely intermediate host and/or mixing vessel for novel flu viruses.
While deemed less likely, other mammals - including cats, dogs, and horses - were also reviewed, and their potential ranked.
Over the years we've looked at an even wider (and growing) array of potential intermediate hosts for novel flu, including seals, bats, and even rabbits. But one of the relatively obscure species we seem to come back to most often are mink. 

Mink farming has become big business in China in recent years, with more than 60 million raised in 2012. Increasingly fox and raccoon dogs are raised on the same farms, increasing the odds of interspecies transmission of novel viruses. 
In China, farmed animals are often fed a diet that includes raw poultry or poultry products (cite), which increases their risk of exposure to avian viruses, while wild mink may consume waterfowl, fish, frogs, and other small mammals.
A decade ago, in 2009's That Touch Of Mink Flu, we looked at a story out of Denmark, where at least 11 mink farms in the Holstebro were reported to be infected with a variant of the human H3N2 virus.
In 2015, we revisited mink flu in That Touch Of Mink Flu (H9N2 Edition), after a study was published in the Virology Journal on a serological survey of antibodies to H9N2 (along with H5 & H7 viruses) in Chinese farmed minks, along with the results of experimental infection of minks with the H9N2 virus.
We've returned to H9N2 in minks at least twice since then (see H9N2 Adaptation In Minks) and That Touch Of Mink Flu (H9N2) - Revisited.
Today we've an open-access research article published by Nature that examines the fitness of a number of small semiaquatic mammals to serve as intermediate hosts - and potential mixing vessels - for novel flu.
The authors posit that some semiaquatic mammals - but most particularly mink - should be considered, along with pigs, as potential sentinels for novel flu.
First some excerpts from a much longer article (you'll want to follow the link to read it in its entirety), and then I'll return with a postscript on another (non-mink) semiaquatic mammal discovered in Russia to be carrying a worrisome flu virus.
Semiaquatic mammals might be intermediate hosts to spread avian influenza viruses from avian to human
Ping Zhao, Lingsha Sun, Jiasheng Xiong, Chuan Wang, Liang Chen, Pengfei Yang, Hao Yu, Qingli Yan, Yan Cheng, Lufang Jiang, Yue Chen, Genming Zhao, Qingwu Jiang & Chenglong Xiong

Avian influenza A viruses (AIVs) can occasionally transmit to mammals and lead to the development of human pandemic. A species of mammal is considered as a mixing vessel in the process of host adaptation. So far, pigs are considered as a plausible intermediate host for the generation of human pandemic strains, and are labelled ‘mixing vessels’.

In this study, through the analysis of two professional databases, the Influenza Virus Resource of NCBI and the Global Initiative on Sharing Avian Influenza Data (GISAID), we found that the species of mink (Neovison vison) can be infected by more subtypes of influenza A viruses with considerably higher α-diversity related indices.

It suggested that the semiaquatic mammals (riverside mammals), rather than pigs, might be the intermediate host to spread AIVs and serve as a potential mixing vessel for the interspecies transmission among birds, mammals and human. In epidemic areas, minks, possibly some other semiaquatic mammals as well, could be an important sentinel species for influenza surveillance and early warning.

This study demonstrates that mink (Neovison vison) might be a potential mixing vessel or intermediate host for the generation of novel human IAVs. Minks, possibly some other semiaquatic mammals (riverside mammals) as well, might play a pivotal role in the process of adapting and transmitting AIVs to human and other terrestrial animals. The significances of mink and other riverside mammal hosts in influenza surveillance and early warning should be paid an attention. In epidemic areas, mink should be considered as one of important sentinel species of hosts for influenza surveillance.

There are several limitations of our study should be mentioned. In this study, we only used the existing databases with no additional laboratory evidence. Secondly, the number of IAVs established from the mammalian species here including those in minks is still small. Hence, our conclusions need to be consolidated.

(Continue . . . )

One of the `other' semiaquatic mammals mentioned in this article are muskrat,  which often share the same or similar habitat as mink. More of an omnivore than the carnivorous mink, they still have occasional contact with waterfowl.
In 2017, in H2N2: Everything Old Is Flu Again, we saw a study published in The Journal Of Veterinary Medical Science, which detailed the finding of H2N2 in Siberian Muskrats. (see Genetic characterization of an H2N2 influenza virus isolated from a muskrat in Western Siberia).
H2N2 is of particular concern because it sparked the Asian Flu pandemic of 1957, and reigned as the sole circulating human influenza A virus until 1968, when it was supplanted by H3N2. 
In 2012, in H2N2: What Went Around, Could Come Around Again, we looked at a study conducted by researchers at St. Jude Children's Research Hospital - published in the Journal of Virology - that concluded that H2N2 - which persists in wild birds - could pose a threat to humanity once again.
While numerous factors - like closer contact and frequent cross-infection between pigs and people, the endemicity of H1, H2, and H3 viruses in pigs, and the high density and movement of farmed animals - favor swine as being the most likely incubator of the next pandemic flu virus, there are dozens of other species capable of contributing to the process as well.

A complex ecology which combine to make another pandemic all but inevitable.