Over the years we’ve looked at a number of examples of infection of small mammals with various types of HPAI avian flu, and the potential they have for vectoring - or even aiding and abetting the evolution of - these viruses.
By far, the most work has been done with the H5N1 virus, as it has been the biggest avian flu threat for the longest period of time.
Domestic animals, like dogs and cats, are of particular interest due to their close relationships and exposure to humans (see Catch as Cats Can). But many other small animals (see USGS List of Species Affected by H5N1 (Avian Influenza) have been discovered to be infected over the years.
But it isn’t just H5N1, or other varieties of HPAI H5, that can infect non-avian species.
Just last week in That Touch Of Mink Flu (H9N2 Edition) we looked at the prevalence of H9N2 in China’s farmed mink industry, while last May in Taking HPAI To The Bank (Vole) we looked at the susceptibility of the European bank vole to both H5 and H7 avian viruses.
We’ve previously seen evidence that H7N9 can infect, and be spread by common lab animals (see H7N9 Transmission and Replication In The Guinea Pig Model), but far less is known about its ability infect small mammals in the wild.
Today from the journal Virology, we get yet another study, this time on H7N9’s ability to infect, and to be shed by, peridomestic animals like skunks, raccoons, and rabbits.
J. Jeffrey Roota, , 1, , Angela M. Bosco-Lauthb, 1, Helle Bielefeldt-Ohmannc, Richard A. Bowenb
- • Common peridomestic mammal species shed H7N9 influenza A virus (IAV).
- • Certain mammalian species shed H7N9 IAV for long periods.
- • Mammals should be taken into account in biosecurity plans for H7N9 IAV.
During 2013, a novel avian-origin H7N9 influenza A virus (IAV) emerged in China and subsequently caused large economic and public health burdens. We experimentally infected three common peridomestic wild mammals with H7N9 (A/Anhui/1/2013) IAV. Striped skunks exhibited the highest burden of disease followed by raccoons and cottontail rabbits.
Striped skunks also produced the highest levels of viral shedding (up to 106.4 PFU/mL nasal flush) followed by cottontail rabbits (up to 105.8 PFU/mL nasal flush) and raccoons (up to 105.2 PFU/mL nasal flush).
Thus, various mammalian species, especially those that are peridomestic, could play a role in the epidemiology of emergent H7N9 IAV. Mammals should be accounted for in biosecurity plans associated with H7N9 and their presence in wet markets, dependent on species, could lead to increased transmission among interspecific species aggregations and may also pose an elevated zoonotic disease risk to visitors and workers of such markets.
Unlike the HPAI H5 avian viruses which cause high mortality in domesticated birds, H7N9 is a stealth virus, infecting and spreading in poultry without producing illness. Often our first clue that H7N9 has infected a flock of farmed birds in China comes when local human infections are reported.
Of the three peridomestic animals tested above, the striped skunk was the most affected by the H7N9 virus, and shed the greatest amount of the virus.
Those with long memories will recall that back in 2010 – in Mixing Vessels For Influenza - we looked at research by two experts from the San Diego Zoo ( Mark Schrenzel and Bruce Rideout) that identified the North American Striped Skunk - along with a handful of other small carnivores - as a potential hosts for influenza reassortment.
Also in 2010, in A Host Of Reservoirs we looked at a letter published in the CDC’s EID Journal detailing the detection of Pandemic (H1N1) 2009 in Skunks, Canada, which highlights this species’ susceptibility to `humanized’ flu viruses as well.
Like pigs, skunks possess both a2,3 avian and a2,6 mammalian receptor cells, making it a potential mixing vessel for influenza reassortment. They do seem somewhat less likely than pigs to be exposed to human flu strains, however.
While an avian virus, H7N9 is notable for the number of `mammalian’ adaptations it has picked up over the past few years. Genetic changes that make it more likely to infect non-avian species, and that increase its pandemic potential.
Adaptation of H7N9 virus to mammals
The genomes of avian influenza A(H7N9) virus contain several features indicating adaptation to mammals as previously identified in other influenza A viruses. Viral adaptations to mammals include increased:
- capacity to bind to cells in the upper respiratory tract of mammals (avian influenza viruses preferentially bind to cells in the intestinal tract of birds); and
- ability to grow at the lower temperature of the upper respiratory tract of mammals (compared to the higher temperature of the intestinal tract of birds).
How the H7N9 virus acquired these adaptations is unknown. How these adaptations will affect virus growth and transmission in various bird species is also unknown.
The avian influenza A(H7N9) virus has been detected in several bird species, the current degree of virus spread in poultry is unknown. The potential for future spread in poultry or even in wild bird species is currently under assessment.
Although its full impact on China’s population is difficult to gauge, as only the `sickest of the sick’ are ever tested, laboratory confirmed H7N9 has been found in nearly 700 people over the past 3 winters.
Thus far, however, we’ve seen no evidence of sustained or efficient human-to-human transmission.
Whether H7N9 - or any of the other non-H1,H2 & H3 flu subtypes - can adapt well enough to human physiology to spark a pandemic remains a topic of considerable debate, which we explored in Are Influenza Pandemic Viruses Members Of An Exclusive Club?.
While it doesn’t answer the question of H7N9’s pandemic potential, today’s study increases the known host range of avian H7N9, and offers fair warning to poultry operations (wet markets, farms, etc.) in China to beef up their biosecurity against the intrusion by small mammals.