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While avian influenza is primarily a disease of birds, and only occasionally spills over into humans, the role played by small mammals in its ecology and evolution remains only partially explored.
Last May, in Report: Skunks and Rabbits Can Catch And Shed Avian Flu, we looked at research by Dr. Jeffrey root on infection and shedding of avian flu by peridomestic animals.
And last year, in Taking HPAI To The Bank (Vole), we looked at research showing voles were not only susceptible to two types of avian flu viruses (H5N1 & H7N1), were able to carry the virus asymptomatically, shed the virus in copious amounts, and could pass on the virus to naïve co-housed sentinel voles.
Small mammals are frequently found roaming around live bird markets, on poultry farms, and drinking from the same water sources in the wild as migratory birds. All places where they could conceivably either pick up - or spread - avian flu viruses.
Asymptomatic carriage by small mammals could also allow these avian viruses to pick up additional mammalian adaptations, which could increase their host range and potentially, their threat to public health.
One species that keeps coming up in the literature is the plateau pika - a small burrowing rabbit-like mammal - found in Tibet and China.
In 2009 a study in the Journal of Virology found that Wild Pikas were Natural Hosts of H5N1 Avian Influenza Virus in Qinghai, China. While in 2014 LPAI H9N2 was found in Pikas at Qinghai Lake, China.
Qinghai lake is somewhat famous as the site of several major avian flu reassortments and large die offs of birds. In 2005 H5N1 clade 2.2 appeared there, followed four years later by clade 2.3.2 (see 2011 EID Journal New Avian Influenza Virus (H5N1) in Wild Birds, Qinghai, China).
All of which brings us to a new report in Nature which finds phylogenetically similar avian H7N2 viruses in wild birds and pikas in the Qinghai lake region, further suggesting a role of pikas in the ecology of avian influenza viruses.
Characterization of H7N2 Avian Influenza Virus in Wild Birds and Pikas in Qinghai-Tibet Plateau Area
Shuo Su, Gang Xing, Junhua Wang, Zengkui Li, Jinyan Gu, Liping Yan, Jing Lei, Senlin Ji, Boli Hu, Gregory C. Gray, Yan Yan & Jiyong Zhou
Abstract
Qinghai Lake is a major migrating bird breeding site that has experienced several recent highly pathogenic avian influenza virus (HPAIV) epizootics. From 2006 to 2009 we studied Qinghai’s wild birds and pikas for evidence of AIV infections.
We sampled 941 healthy wild animals and isolated seventeen H7N2 viruses (eight from pikas and nine from wild birds). The H7N2 viruses were phylogenetically closely related to each other and to viruses isolated in Hong Kong in the 1970s. We determined the pathogenicity of the H7N2 viruses by infecting chickens and mice.
Our results suggest that pikas might play an important role in the ecology of AIVs, acting as intermediate hosts in which viruses become more adapted to mammals. Our findings of AI infection in pikas are consistent with previous observations and raise the possibility that pikas might play a previously unrecognized role in the ecology of AIVs peridomestic aquatic environments.
Su, S. et al. Characterization of H7N2 Avian Influenza Virus in Wild Birds and Pikas in Qinghai-Tibet Plateau Area. Sci. Rep. 6, 30974; doi: 10.1038/srep30974 (2016).
These H7N2 viruses were LPAI, and not related to the H7N9 viruses that emerged in China in 2013.
As the authors point out, it is a bit of a mystery how these H7N2 viruses could have become enzootic in this region yet we've seen no reports of their detection in domestic poultry.
They write:
Perhaps this is due to limited AIV surveillance among poultry in this area. It seems logical that if AIVs are enzootic among the many wild birds in the Qinghai-Tibet plateau area, especially around the Qinghai Lake area, infections in other wild and domestic animals are likely occurring but unrecognized. More extensive AIV surveillance among Qinghai Lakes migrating birds, wild mammals, and domestic animals seems imperative.
More evidence to suggest that what we don't know about avian flu could still fill volumes.
