Zoonotic Transmission of Influenza H9 subtype through Reassortment
Kimble, James Brian
Perez, Daniel R
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Influenza A virus causes disease across a broad host range including avian and mammalian species. Most influenza viruses are found in wild aquatic birds, are of low consequence and refrain from zoonotic transmission. However, some strains occasionally cross the species barrier, into domestic birds and a plethora of mammalian species, most notably swine and humans. Many of these infections are dead ends and quickly disappear from the species, but occasionally, a stable lineage is established and becomes endemic in an animal population. Avian Influenza virus (AIV) H9N2 was predominantly found in wild ducks and shore birds across the globe with occasional infections in turkeys until the late 1980's, at which point the virus became established in Eurasian poultry populations. In the late 1990's the virus again jumped hosts, first into swine, and then into humans. Across many regions, these viruses appear to be gaining human-like virus characteristics. Here, the influenza receptor distribution in a range of poultry species has been characterized and shown that many of the birds were able to bind human-like binding viruses. While no large-scale H9N2 human infections have occurred, the threat is there. The most likely route for this to occur is through reassortment with human viruses. The 2009 human pandemic H1N1 (pH1N1) is a likely candidate as it is found in multiple species and seems to readily reassort. The two viruses were shown to be compatible for reassortment and H9:pH1N1 viruses would readily infect and transmit in both ferrets (a human model animal) and swine. Finally, a novel method of modeling reassortment in vivo was developed, which simultaneously tests the breadth of possible reassortant and utilizes natural host selective pressure to select the most-fit progeny. Furthermore, the characterization of these viruses in ferrets showed they readily infect, efficiently transmit, and exhibit mild to moderate pathological consequences. Taken together, these findings broaden our understanding of natural observations, characterize the potential for zoonosis, highlight the dangers H9 viruses may pose to humans, and give scientists a new tool to deepen our understanding of reassortment.