Reverse zoonosis of influenza to swine: new perspectives on the human–animal interface

Abstract

The origins of the influenza A (H1N1) pandemic of 2009 in swine are unknown, highlighting gaps in our understanding of influenza A virus ecology and evolution. Here we review how recently strengthened influenza virus surveillance in pigs has revealed that influenza virus transmission from humans to swine is far more frequent than swine-to-human zoonosis, and is central in seeding swine globally with new viral diversity. The scale of global human-to-swine transmission represents the largest ‘reverse zoonosis’ of a pathogen documented to date. Overcoming the bias towards perceiving swine as sources of human viruses, rather than recipients, is key to understanding how the bidirectional nature of the human-animal interface produces influenza threats to both hosts.

Origin, distribution, and potential risk factors associated with influenza A virus in swine in two production systems in Guatemala

“…The role of humans in the epidemiology of swine IAV has been increasingly recognized due to the accumulating evidence of reverse zoonotic transmission events observed over the past century 3. Information on the prevalence and distribution of swine IAVs remains limited in many regions of the world, particularly in Latin America 4.…”

The avian‐origin H3N2 canine influenza virus that recently emerged in the United States has limited replication in swine

“…However, pigs generally have low susceptibility to direct infection with avian, equine, and canine IAV 13. Consistent with these findings, an in vitro and in vivo study found that pigs are more susceptible to avian and seal H3N8 than to equine and canine H3N8 14.…”

Influenza in Brazil: surveillance pathways

“…The pandemic influenza virus of 2009 was described in both domestic and non-domestic animals, such as in giant pandas in China [35] and swine in Brazil [36,37] and in other countries such as Australia, India, Sri Lanka, Colombia, and Cameroon [38]. Many studies emphasize the importance of knowledge about animal influenza to the disease in humans.…”

“…Nelson & Vincent [38] emphasize the biases -of the sample, time, and space -in the surveillance of influenza in humans and swine given that the imbalance of the surveillance activities affects the understanding of viral ecology. The authors state the necessity of intensifying the surveillance of influenza in swine, especially in countries that have large populations of these animals, and with reduced surveillance such as in Brazil, Vietnam, and Russia.…”