History of Swine Influenza Viruses in Asia

Abstract

The pig is one of the main hosts of influenza A viruses and plays important roles in shaping the current influenza ecology. The occurrence of the 2009 H1N1 pandemic influenza virus demonstrated that pigs could independently facilitate the genesis of a pandemic influenza strain. Genetic analyses revealed that this virus was derived by reassortment between at least two parent swine influenza viruses (SIV), from the northern American triple reassortant H1N2 (TR) and European avian-like H1N1 (EA) lineages. The movement of live pigs between different continents and subsequent virus establishment are preconditions for such a reassortment event to occur. Asia, especially China, has the largest human and pig populations in the world, and seems to be the only region frequently importing pigs from other continents. Virological surveillance revealed that not only classical swine H1N1 (CS), and human-origin H3N2 viruses circulated, but all of the EA, TR and their reassortant variants were introduced into and co-circulated in pigs in this region. Understanding the long-term evolution and history of SIV in Asia would provide insights into the emergence of influenza viruses with epidemic potential in swine and humans.

Emergence and Dissemination of a Swine H3N2 Reassortant Influenza Virus with 2009 Pandemic H1N1 Genes in Pigs in China

“…Before these isolates, H3N2 swine influenza viruses had not been detected in the last 6 years in our ongoing surveillance program (9,23,25). The viruses isolated here and those from recent reports (2, 10, 14) from other regions of a small number of swine H3N2 viruses had HA genes more closely related to those of human seasonal strains from 1995 to 2004.…”

“…All three viruses were isolated in MDCK cells and subtyped, and full genome sequences of these three H3N2 swine isolates were obtained as previously described (22,23,26). These are the first H3N2 swine viruses isolated since 2005 in our ongoing surveillance program in southern China (9,23,25).…”

Review on Swine Flu and Status of Swine Flu in Ethiopia

“…The viruses are thought to be enzootic in most areas that have dense populations of pigs, but they might remain undetected in some regions, as infected herds can be asymptomatic or have only mild clinical sig [21][22][23]. Swine flu has been terror effects of all-round the globe and has been declared epidemic in most part of the world.…”

Influenza Virus Infection in Pigs

“…Most swine IAV circulating in Europe are also found in Asia, but there are several viral strains that are found only in Asia. China is a key point in the epidemiology of IAV in Asia, due to the high density and extensive pig production, but also because management practices (Zhu et al, 2011). IAV isolated from pigs in China include cH1N1, H1N1pdm09, Eurasian H3N2, H3N2 of human origin or North American H3N2, H1N1 Eurasian and H1N2 containing the TRIG, among others.…”

“…IAV isolated from pigs in China include cH1N1, H1N1pdm09, Eurasian H3N2, H3N2 of human origin or North American H3N2, H1N1 Eurasian and H1N2 containing the TRIG, among others. Thus, China isolates include IAV from North America and Europe, reassortants IAV from North America and Europe and IAV of avian origin only (Zhu et al, 2011). Thus, China isolates include IAV from North America and Europe, reassortants IAV from North America and Europe and IAV of avian origin only.…”