tetano
Editor, Senior Moderator
Introduction
Influenza A viruses (IAVs) are one of the most intensively studied pathogens, due to the severe global mortality and economic disruption associated with influenza pandemics [1]. In addition to annual epidemics, pandemics sporadically occur when a novel IAV host jumps to humans from an animal reservoir [2]. Wild waterfowl have long been considered the most important reservoir host and pandemic risk, but there are indications that mammals are emerging as key reservoirs. Here, we describe how the modernization of swine production during the last half century provided new opportunities for IAVs to become established in swine globally [3–5], resulting in the first influenza pandemic of swine origin in 2009 [6]. A key lesson is that the landscape of pandemic risk is not static but continuously shifting in response to demographic changes in host populations. It is therefore vital to track how transformations in the economy and global trade impact animal contact rates, disease dynamics, and pandemic risk among livestock and companion animals.
Pigs fly?
For centuries, domestic pigs (Sus scrofa domesticus) were raised on traditional small-scale farms that could not sustain IAV transmission. Whereas horses and people traveled frequently within and between urban areas, causing recurrent influenza outbreaks in both species as far back as the 13th century [7], influenza was not maintained in any country’s swine population until 1918, when the Spanish influenza H1N1 pandemic virus was introduced from humans into swine in the United States [8]. The H1N1 virus circulated in US swine for most of the 20th century without substantially evolving, causing severe disease, or becoming endemic in swine in other countries.
In the latter decades of the 20th century, the replacement of small-scale swine farms with larger, more efficient production systems (Fig 1A) had profound effects on disease dynamics. Enhanced biosecurity improved control of important pathogens, such as hog cholera. But modern production systems often require pigs to be transported long distances between multiple locations specialized in different growth stages, facilitating the spread of IAV in swine (IAV-S; commonly known as swine flu) and other pathogens not specifically targeted for eradication. For example, many large breeding operations located in the southern US find it more efficient to transport fattening pigs to the Midwest “corn belt” than to transport the large volumes of feed back to the south. By the 2000s, trucks were transporting millions of pigs long distances across North America, facilitating the spread of IAV-S along established “swineways” [9].
full article
https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1008259
Influenza A viruses (IAVs) are one of the most intensively studied pathogens, due to the severe global mortality and economic disruption associated with influenza pandemics [1]. In addition to annual epidemics, pandemics sporadically occur when a novel IAV host jumps to humans from an animal reservoir [2]. Wild waterfowl have long been considered the most important reservoir host and pandemic risk, but there are indications that mammals are emerging as key reservoirs. Here, we describe how the modernization of swine production during the last half century provided new opportunities for IAVs to become established in swine globally [3–5], resulting in the first influenza pandemic of swine origin in 2009 [6]. A key lesson is that the landscape of pandemic risk is not static but continuously shifting in response to demographic changes in host populations. It is therefore vital to track how transformations in the economy and global trade impact animal contact rates, disease dynamics, and pandemic risk among livestock and companion animals.
Pigs fly?
For centuries, domestic pigs (Sus scrofa domesticus) were raised on traditional small-scale farms that could not sustain IAV transmission. Whereas horses and people traveled frequently within and between urban areas, causing recurrent influenza outbreaks in both species as far back as the 13th century [7], influenza was not maintained in any country’s swine population until 1918, when the Spanish influenza H1N1 pandemic virus was introduced from humans into swine in the United States [8]. The H1N1 virus circulated in US swine for most of the 20th century without substantially evolving, causing severe disease, or becoming endemic in swine in other countries.
In the latter decades of the 20th century, the replacement of small-scale swine farms with larger, more efficient production systems (Fig 1A) had profound effects on disease dynamics. Enhanced biosecurity improved control of important pathogens, such as hog cholera. But modern production systems often require pigs to be transported long distances between multiple locations specialized in different growth stages, facilitating the spread of IAV in swine (IAV-S; commonly known as swine flu) and other pathogens not specifically targeted for eradication. For example, many large breeding operations located in the southern US find it more efficient to transport fattening pigs to the Midwest “corn belt” than to transport the large volumes of feed back to the south. By the 2000s, trucks were transporting millions of pigs long distances across North America, facilitating the spread of IAV-S along established “swineways” [9].
full article
https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1008259