Large outbreak of swine influenza in southern Japan caused by reassortant (H1N2) influenza viruses: its epizootic background and characterization of the causative viruses

Abstract

In the winter of 1989 and the spring of 1990, there were large outbreaks of respiratory disease in two swine herds in Nagasaki Prefecture, southern Japan. Serological surveillance indicated that the majority of swine possessed antibodies to swine influenza virus H 1 haemagglutinin and neuraminidase of early H3N2 influenza virus strains. Eight viruses were isolated from swine that showed typical clinical symptoms of influenza. The haemagglutinin and neuraminidase of these isolates were closely related to those of swine HIN1 and early human H3N2 viruses, respectively. At least two types of haemagglutinin antigens, distinguished by two monoclonal antibodies, were involved in the outbreaks. Evolutionary analyses indicated that the haemagglutinin gene of the H1 N2 reassortants was closely related to those of a recent swine lineage (A/sw/HK/1/74 and A/sw/Ehime/1/80 viruses). However, the neuraminidase genes of the HI N2 reassortants were similar to those of swine N2 viruses which in turn are related to early human H3N2 viruses. A comparison of partial nucleotide sequences revealed that the six other genes of A/sw/Nagasaki/ 1/89 were derived from those of swine H 1 N 1 virus.

Multiple genetic reassortment of avian and human influenza A viruses in European pigs, resulting in the emergence of an H1N2 virus of novel genotype.

“…Influenza viruses of H1N2 subtype have been described in pigs previously from both Europe (Gourreau et al, 1994) and Asia (Sugimura et al, 1980), with increasing prevalence in Japan (Ouchi et al, 1996). All of these viruses are derived from cocirculating swine strains of H1N1 and ' human-like ' H3N2 viruses, and are therefore clearly distinguishable both antigenically and genetically from the swine H1N2 viruses isolated recently in GB.…”

Molecular Characterization of an H1N2 Swine Influenza Virus Isolated in Miyazaki, Japan, in 2006

“…The genetic constellation of Sw/ Miyazaki/1/2006 and most of above-mentioned Japanese SIVs could not be compared directly because entire gene sequences of the internal genes are not available for those viruses. However, previous studies have demonstrated that the internal genes of the Japanese H1N2 viruses isolated from 1980 to 1992 (Sw/Ehime/1/1980, Sw/Nagasaki/1/ 1989, Sw/Nagasaki/1/90) [12,15] are closely related to the classical SIVs by comparing partial sequences of the segments, indicating a similar gene constellation to Sw/ Miyazaki/1/2006. Thus, it appears that the H1N2 SIV in Japan have been maintained in the Japanese pig population for almost 30 years, despite occasional introduction events of human H1N1 or H3N2 epidemic strains into the pig population [6,12].…”

Genetic Characterization of H1N2 Influenza A Viruses Isolated from Pigs throughout the United States

“…However, H1N2 viruses were isolated previously from pigs in France in 1987 and 1988 (4), in Japan in 1978 to 1980 and 1989 to 1992 (6, 9, 10, 12, 13, 16), and in the United Kingdom in 1994 and thereafter (1,2). The viruses from Japan and France were shown to be products of reassortment between classical (Japan) or avian-like (France) swine H1N1 viruses and human-lineage H3N2 viruses (4,6,9,10,12,13,16). In contrast, the H1N2 viruses in the United Kingdom resulted from multiple reassortment events.…”

“…Reassortment between human H1N1 and H3N2 viruses is hypothesized to have initially created an H1N2 subtype virus, which subsequently acquired all six of its internal viral protein genes through reassortment with a wholly avian virus (2). The H1N2 viruses in France did not spread beyond their initial farms of origin (4), but the H1N2 viruses in Japan and the United Kingdom caused large-scale outbreaks of disease and spread widely in the swine populations of these countries (1,2,6,12). Most recently it has been shown that H1N2 viruses with HA proteins antigenically related to those of the H1N2 viruses from the United Kingdom are circulating among pigs in Belgium (14).…”