Fifteen years ago, when I began writing about pandemic influenza, H5N1 avian flu was at the top of our worry list - hence the title of this blog. But since then, we've learned a great deal more about the prevalence of - and potential risks from - other zoonotic influenzas.
Over the past 14,000+ blogs, we've looked at novel flu viruses in pigs, dogs, cats, horses, seals, camels, mink, and even bats (to name but a few).While all of these species - in theory - could host the next pandemic virus, the reality is that not all zoonotic flu threats are created equal.
As we've discussed often over the past few years (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?), the progression of human influenza pandemics over the past 130 years has been H2, H3, H1, H2, H3, H1, H1 . . . .
While the threat of an avian H5 or H7 pandemic can't be ignored - particularly because of its potential severity - based on recent history, it probably isn't the most likely scenario.
Simply put, novel H1, H2, and H3 flu viruses appear to have fewer barriers to overcome in order to jump to humans - and while they may not prove as virulent as H5 & H7 avian subtypes - that puts them at or near the top of our threats list.Add in the fact that pigs are the biggest reservoir species for novel H1, H2, and H3 influenza viruses, and they become the species to watch.
A little over three years ago, Chen Hualan - director of China's National Avian Influenza Reference Laboratory - pegged the EA (Eurasian Avian-like) H1N1 swine virus (EAH1N1) as having perhaps the greatest pandemic potential of any of the novel viruses in circulation.
Avian-like H1N1 swine flu may "pose highest pandemic threat": studyHer comments came after the publication of her paper Prevalence, genetics, and transmissibility in ferrets of Eurasian avian-like H1N1 swine influenza viruses. Some other, more recent studies, we've examined include:
WASHINGTON, Dec. 28 (Xinhua) -- The Eurasian avian-like H1N1 (EAH1N1) swine flu viruses, which have circulated in pigs since 1979, have obtained the ability to infect humans and may "pose the highest pandemic threat" among the flu viruses currently circulating in animals, Chinese researchers said Monday.
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PLoS One: Continuous Evolution of Influenza A Viruses of Swine from 2013 to 2015 in Guangdong, China
J.O.I. : A Human Infection with a Novel Reassortant H3N2 Swine Virus in China
Emerg. Infect. & Microbes: Novel Triple-Reassortant influenza Viruses In Pigs, Guangxi, China
Despite the fact that the 2009 H1N1 pandemic was sparked by a triple reassortant swine-origin virus, and numerous studies showing a growing number of novel strains in circulation around the world, testing and surveillance remain severely limited.
All of which brings us to an open-access review - published in the International Journal of Infectious Diseases - of zoonotic influenza threats, along with recommendations on future surveillance.
Laura K. Borkenhagen, Mo D. Salman, Mai-Juan Ma, Gregory C. Gray
Open Access Animal Influenza Virus Infections in Humans: A Commentary
Domesticated animals, particularly pigs, poultry, and horses, but also recently dogs and cats, are noted to experience influenza infections that have potential to cross species to other animals and to humans.
Swine influenza virus infections are frequently detected among humans with exposure to pigs and become transmissible between humans more often than avian influenza viruses.
There remains a great need to broker One Health-oriented, routine influenza virus surveillance within large swine farms and other pork production points worldwide.
Development of non-invasive sampling techniques and diagnostics that offer rapid characterization of influenza viruses would benefit both agricultural industries and public health.
Here we review evidence for influenza A viruses (IAVs) moving from swine, avian, feline, equine, and canine species to infect humans. We review case reports, sero-epidemiological, archeo-epidemiological, environmental, and historical studies and consider trends in livestock farming.
Although this focused review is not systematic, the aggregated data point to industrialized swine farming as the most likely source of future pandemic viruses, yet IAV surveillance on such farms is remarkably sparse.
We recommend increased biosafety and biosecurity training for farm administrators and swine workers with One Health-oriented virus surveillance throughout industrialized farming and meat production lines. Collaborative partnerships with human medical researchers could aid in efforts to mitigate emerging virus threats by offering new surveillance and diagnostic technologies to livestock farming industries.
A pre-proof PDF of the full report is available at this link.
The authors submit that swine, followed by avian species, pose the greatest pandemic threat - with companion animals like dogs, cats, and horses - while having some potential, are much further down the list.
The full 25 page PDF is very much worth reading in its entirety.For some of my past blogs on these lesser threats posed by companion animals, you may wish to revisit:
EID Journal: Equine Influenza - A Neglected, Reemergent Disease Threat
Equine H3N8: Looking At A long-shot In The Pandemic Sweepstakes
Access Microbiology: Inter-Species Transmission of Avian Influenza Virus to Dogs
EID Journal: HPAI H5N6 In Domestic Cats - Korea, 2016
J Infect Dis: Serological Evidence Of H7N2 Infection Among Animal Shelter Workers, NYC 2016
Study: Dogs As Potential `Mixing Vessels’ For Influenza