Emily
Editor, Senior Moderator
http://vir.sgmjournals.org/cgi/content/full/88/7/2035
"As pigs are susceptible to infection with both avian and human influenza A viruses, they have been proposed to be an intermediate host for the generation of pandemic virus through reassortment. Antigenic and genetic characterization was performed for five swine H9N2 influenza viruses isolated from diseased pigs from different farms. The haemagglutinin (HA) antigenicity of swine H9N2 viruses was different from that of chicken H9N2 viruses prevalent in northern China. Genetic analysis revealed that all five isolates had an RLSR motif at the cleavage site of HA, which was different from those of A/duck/Hong Kong/Y280/97 (Dk/HK/Y280/97)-like viruses established in chickens in China. Phylogenetic analyses indicated that the five swine H9N2 viruses formed novel HA and neuraminidase sublineages that were related closely to those of earlier chicken H9 viruses and were also consistent with the extent of the observed antigenic variation. The six internal genes of the isolates possessed H5N1-like sequences, indicating that they were reassortants of H9 and H5 viruses. The present results indicate that avian to porcine interspecies transmission of H9N2 viruses might have resulted in the generation of viruses with novel antigenic and genetic characteristics; therefore, surveillance of swine influenza should be given a high priority.
The GenBank/DDBJ/EMBL accession numbers for the nucleotide sequences of the H9N2 influenza viruses analysed in this study are DQ981591?DQ981630.
Influenza A viruses are classified into a number of subtypes based on antigenic differences in their two surface glycoproteins, haemagglutinin (HA; 16 subtypes) and neuraminidase (NA; nine subtypes) (Fouchier et al., 2005Down; Webster et al., 1992Down). The H9N2 subtype virus is a conspicuous member of the influenza family because it can infect not only chickens, ducks and pigs, but also humans (Guo et al., 2000Down; Liu et al., 2003Down; Peiris et al., 1999Down; Xu et al., 2004Down). In China, the H9N2 virus was first isolated from a chicken in 1992 in Guangdong province (Chen et al., 1994Down) and is now the most prevalent subtype of influenza virus in poultry in China. Recent studies have shown that the H9N2 viruses can infect pigs and cause significant morbidity and mortality (Xu et al., 2004Down). However, the detailed characteristics of the viruses, such as antigenicity and phylogenetic properties, are not well defined.
Pigs are thought to be susceptible to infection with both avian and human influenza A viruses because the cells of their respiratory tract express both sialic acid-{alpha}2,3-galactose (SA{alpha}2,3Gal) receptors, preferred by avian influenza viruses, and sialic acid-{alpha}2,6-galactose (SA{alpha}2,6Gal) receptors, preferred by human influenza viruses (Ito et al., 1998Down). Thus, pigs are proposed to be ?mixing vessels? for the generation of reassortant influenza viruses with pandemic potential (Brown et al., 1998Down; Castrucci et al., 1993Down; Scholtissek et al., 1985Down; Webster et al., 1992Down). The broad susceptibility of pigs to many influenza viruses emphasizes the importance of surveillance of swine influenza viruses as possible sources of pandemic influenza. This concern is heightened by the presence of not only H1N1 and H3N2 strains from human sources, but also avian influenza virus strains, in both American and Eurasian herds of pigs (Brown, 2000Down). Coinfections have allowed intermixing of these genomes to produce triple reassortants with genes derived from human, swine and avian influenza strains (Olsen et al., 2006Down). As porcine viruses become more human-like as well as more avian-like, the probability of generating human-adaptive viruses increases. Here, we describe the genetic composition of swine influenza strains in China that comprise avian H9N2-like and H5N1-like genome segments.
Swine influenza outbreaks occurred in Shandong province, China, in 2003. At that time, most of the diseased pigs showed typical respiratory signs, such as fever, nasal and ocular discharge, coughing and dyspnoea; however, paralysis associated with fatal disease was also observed. Laboratory diagnosis and virus isolation demonstrated that the disease resulted from infection with subtype H9N2 influenza viruses. To elucidate the antigenic and genetic characteristics of these viruses and the relationship of the swine H9N2 viruses with avian influenza viruses, we analysed five H9N2 swine influenza virus isolates antigenically and genetically.
.....
The present findings indicated that the H9N2 viruses in the study were reassortants of H9 and H5 viruses. Although we do not know which viral factors are necessary for interspecies transmission, reassortment is likely to increase the chances of generating transmissible viruses. In southern China, at least 2 % of blood donors tested were positive for H9 antibodies (Butt et al., 2005Down; Guo et al., 1999Down; Nicholson et al., 2003Down; Peiris et al., 1999Down), suggesting that human infection with H9N2 occurs ubiquitously in this area. As H9N2 virus appears to have the potential to cross the species barrier to humans more efficiently than the current H5N1 virus as a result of its predicted affinity for NeuAc{alpha}2,6Gal receptors (Butt et al., 2005Down; Ha et al., 2001Down; Kaverin et al., 2004Down; Li et al., 2003Down; Matrosovich et al., 2004Down), swine H9N2 viruses, especially reassortants of H9 and H5 viruses, should be highlighted as candidates for human pandemic influenza viruses."
I don't know if all subsequent reports involve paralysis, but there are several reports of these H9N2 outbreaks in swine in China.
http://www.ncbi.nlm.nih.gov/pubmed/18403137
Isolation and genetic characterization of avian origin H9N2 influenza viruses from pigs in China.
Yu H, Hua RH, Wei TC, Zhou YJ, Tian ZJ, Li GX, Liu TQ, Tong GZ.
National Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, China.
"As pigs are susceptible to infection with both avian and human influenza A viruses, they have been proposed to be an intermediate host for the adaptation of avian influenza viruses to humans. In April 2006, a disease caused by highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV) occurred in several pig farms and subsequently overwhelmed almost half of China with more than 2,000,000 cases of pig infection. Here we report a case in which four swine H9N2 influenza viruses were isolated from pigs infected by highly pathogenic PRRSVs in Guangxi province in China. All the eight gene segments of the four swine H9N2 viruses are highly homologous to A/Pigeon/Nanchang/2-0461/00 (H9N2) or A/Wild Duck/Nanchang/2-0480/00 (H9N2). Phylogenetic analyses of eight genes show that the swine H9N2 influenza viruses are of avian origin and may be the descendants of A/Duck/Hong Kong/Y280/97-like viruses. Molecular analysis of the HA gene indicates that our H9N2 isolates might have high-affinity binding to the alpha2,6-NeuAcGal receptor found in human cells. In conclusion, our finding provides further evidence about the interspecies transmission of avian influenza viruses to pigs and emphasizes the importance of reinforcing swine influenza virus (SIV) surveillance, especially after the emergence of highly pathogenic PRRSVs in pigs in China."
Immune suppression by PRRSV preceded and may be interacting with SIV evolution.
"As pigs are susceptible to infection with both avian and human influenza A viruses, they have been proposed to be an intermediate host for the generation of pandemic virus through reassortment. Antigenic and genetic characterization was performed for five swine H9N2 influenza viruses isolated from diseased pigs from different farms. The haemagglutinin (HA) antigenicity of swine H9N2 viruses was different from that of chicken H9N2 viruses prevalent in northern China. Genetic analysis revealed that all five isolates had an RLSR motif at the cleavage site of HA, which was different from those of A/duck/Hong Kong/Y280/97 (Dk/HK/Y280/97)-like viruses established in chickens in China. Phylogenetic analyses indicated that the five swine H9N2 viruses formed novel HA and neuraminidase sublineages that were related closely to those of earlier chicken H9 viruses and were also consistent with the extent of the observed antigenic variation. The six internal genes of the isolates possessed H5N1-like sequences, indicating that they were reassortants of H9 and H5 viruses. The present results indicate that avian to porcine interspecies transmission of H9N2 viruses might have resulted in the generation of viruses with novel antigenic and genetic characteristics; therefore, surveillance of swine influenza should be given a high priority.
The GenBank/DDBJ/EMBL accession numbers for the nucleotide sequences of the H9N2 influenza viruses analysed in this study are DQ981591?DQ981630.
Influenza A viruses are classified into a number of subtypes based on antigenic differences in their two surface glycoproteins, haemagglutinin (HA; 16 subtypes) and neuraminidase (NA; nine subtypes) (Fouchier et al., 2005Down; Webster et al., 1992Down). The H9N2 subtype virus is a conspicuous member of the influenza family because it can infect not only chickens, ducks and pigs, but also humans (Guo et al., 2000Down; Liu et al., 2003Down; Peiris et al., 1999Down; Xu et al., 2004Down). In China, the H9N2 virus was first isolated from a chicken in 1992 in Guangdong province (Chen et al., 1994Down) and is now the most prevalent subtype of influenza virus in poultry in China. Recent studies have shown that the H9N2 viruses can infect pigs and cause significant morbidity and mortality (Xu et al., 2004Down). However, the detailed characteristics of the viruses, such as antigenicity and phylogenetic properties, are not well defined.
Pigs are thought to be susceptible to infection with both avian and human influenza A viruses because the cells of their respiratory tract express both sialic acid-{alpha}2,3-galactose (SA{alpha}2,3Gal) receptors, preferred by avian influenza viruses, and sialic acid-{alpha}2,6-galactose (SA{alpha}2,6Gal) receptors, preferred by human influenza viruses (Ito et al., 1998Down). Thus, pigs are proposed to be ?mixing vessels? for the generation of reassortant influenza viruses with pandemic potential (Brown et al., 1998Down; Castrucci et al., 1993Down; Scholtissek et al., 1985Down; Webster et al., 1992Down). The broad susceptibility of pigs to many influenza viruses emphasizes the importance of surveillance of swine influenza viruses as possible sources of pandemic influenza. This concern is heightened by the presence of not only H1N1 and H3N2 strains from human sources, but also avian influenza virus strains, in both American and Eurasian herds of pigs (Brown, 2000Down). Coinfections have allowed intermixing of these genomes to produce triple reassortants with genes derived from human, swine and avian influenza strains (Olsen et al., 2006Down). As porcine viruses become more human-like as well as more avian-like, the probability of generating human-adaptive viruses increases. Here, we describe the genetic composition of swine influenza strains in China that comprise avian H9N2-like and H5N1-like genome segments.
Swine influenza outbreaks occurred in Shandong province, China, in 2003. At that time, most of the diseased pigs showed typical respiratory signs, such as fever, nasal and ocular discharge, coughing and dyspnoea; however, paralysis associated with fatal disease was also observed. Laboratory diagnosis and virus isolation demonstrated that the disease resulted from infection with subtype H9N2 influenza viruses. To elucidate the antigenic and genetic characteristics of these viruses and the relationship of the swine H9N2 viruses with avian influenza viruses, we analysed five H9N2 swine influenza virus isolates antigenically and genetically.
.....
The present findings indicated that the H9N2 viruses in the study were reassortants of H9 and H5 viruses. Although we do not know which viral factors are necessary for interspecies transmission, reassortment is likely to increase the chances of generating transmissible viruses. In southern China, at least 2 % of blood donors tested were positive for H9 antibodies (Butt et al., 2005Down; Guo et al., 1999Down; Nicholson et al., 2003Down; Peiris et al., 1999Down), suggesting that human infection with H9N2 occurs ubiquitously in this area. As H9N2 virus appears to have the potential to cross the species barrier to humans more efficiently than the current H5N1 virus as a result of its predicted affinity for NeuAc{alpha}2,6Gal receptors (Butt et al., 2005Down; Ha et al., 2001Down; Kaverin et al., 2004Down; Li et al., 2003Down; Matrosovich et al., 2004Down), swine H9N2 viruses, especially reassortants of H9 and H5 viruses, should be highlighted as candidates for human pandemic influenza viruses."
I don't know if all subsequent reports involve paralysis, but there are several reports of these H9N2 outbreaks in swine in China.
http://www.ncbi.nlm.nih.gov/pubmed/18403137
Isolation and genetic characterization of avian origin H9N2 influenza viruses from pigs in China.
Yu H, Hua RH, Wei TC, Zhou YJ, Tian ZJ, Li GX, Liu TQ, Tong GZ.
National Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, China.
"As pigs are susceptible to infection with both avian and human influenza A viruses, they have been proposed to be an intermediate host for the adaptation of avian influenza viruses to humans. In April 2006, a disease caused by highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV) occurred in several pig farms and subsequently overwhelmed almost half of China with more than 2,000,000 cases of pig infection. Here we report a case in which four swine H9N2 influenza viruses were isolated from pigs infected by highly pathogenic PRRSVs in Guangxi province in China. All the eight gene segments of the four swine H9N2 viruses are highly homologous to A/Pigeon/Nanchang/2-0461/00 (H9N2) or A/Wild Duck/Nanchang/2-0480/00 (H9N2). Phylogenetic analyses of eight genes show that the swine H9N2 influenza viruses are of avian origin and may be the descendants of A/Duck/Hong Kong/Y280/97-like viruses. Molecular analysis of the HA gene indicates that our H9N2 isolates might have high-affinity binding to the alpha2,6-NeuAcGal receptor found in human cells. In conclusion, our finding provides further evidence about the interspecies transmission of avian influenza viruses to pigs and emphasizes the importance of reinforcing swine influenza virus (SIV) surveillance, especially after the emergence of highly pathogenic PRRSVs in pigs in China."
Immune suppression by PRRSV preceded and may be interacting with SIV evolution.
