Abstract
Zoonotic infections of humans with influenza A viruses (IAVs) from animal reservoirs can result in severe disease in individuals and, in rare cases, lead to pandemic outbreaks; this is exemplified by numerous cases of human infection with avian IAVs (AIVs) and the 2009 swine influenza pandemic. In fact, zoonotic transmissions are strongly facilitated by manmade reservoirs that were created through the intensification and industrialization of livestock farming. This can be witnessed by the repeated introduction of IAVs from natural reservoirs of aquatic wild bird metapopulations into swine and poultry, and the accompanied emergence of partially- or fully-adapted human pathogenic viruses. On the other side, human adapted IAV have been (and still are) introduced into livestock by reverse zoonotic transmission. This link to manmade reservoirs was also observed before the 20th century, when horses seemed to have been an important reservoir for IAVs but lost relevance when the populations declined due to increasing industrialization. Therefore, to reduce zoonotic events, it is important to control the spread of IAV within these animal reservoirs, for example with efficient vaccination strategies, but also to critically surveil the different manmade reservoirs to evaluate the emergence of new IAV strains with pandemic potential.
Highlights
In 1977, almost 20 years after its disappearance, a human H1N1 virus re-emerged in northern China causing a minor pandemic outbreak, and has been co-circulating with the H3N2 seasonal strain in the human population ever since [38,39]
Influenza A viruses (IAVs) circulate in a variety of different animal species, livestock animals are becoming especially important as a reservoir for zoonotic IAV transmission
The increased demand for animal products has driven the intensification of livestock farming and led to the introduction, adaptation, spread, and often endemic entrenchment of IAVs in these farmed animals
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The ability of IAVs to rapidly cross interspecies barriers and circulate in a variety of avian and mammalian species of wildlife and livestock creates a breeding ground for zoonotic strains with pandemic potential. Intensification of animal husbandry, increasing encroachment into wildlife habitats for agricultural use, and increased connectivity of livestock populations through (transboundary) trade, created favorable conditions that are associated with the establishment of new IAV lineages in these reservoirs and created new interfaces for human infections [6,7,8,9,10,11]. Some examples include the 2009 pandemic swine influenza virus [12] and an increasing number of reported zoonotic spillover infections with avian IAVs (AIVs) from poultry [13,14]. IAV hosts species, the respective host-human interfaces, and discuss their importance for zoonotic spillover
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