Pandemic (H1N1) 2009 virus on commercial swine farm, Thailand

Multiple reassortment between pandemic (H1N1) 2009 and endemic influenza viruses in pigs, United States

As a result of human-to-pig transmission, pandemic influenza A (H1N1) 2009 virus was detected in pigs soon after it emerged in humans. In the United States, this transmission was quickly followed by multiple reassortment between the pandemic virus and endemic swine viruses. Nine reassortant viruses representing 7 genotypes were detected in commercial pig farms in the United States. Field observations suggested that the newly described reassortant viruses did not differ substantially from pandemic (H1N1) 2009 or endemic strains in their ability to cause disease. Comparable growth properties of reassortant and endemic viruses in vitro supported these observations; similarly, a representative reassortant virus replicated in ferrets to the same extent as did pandemic (H1N1) 2009 and endemic swine virus. These novel reassortant viruses highlight the increasing complexity of influenza viruses within pig populations and the frequency at which viral diversification occurs in this ecologically important viral reservoir.

Multiple reassortment between pandemic (H1N1) 2009 and endemic influenza viruses in pigs, United States

TOC Summary: Viruses belonging to these novel genotypes are indistinguishable phenotypically from endemic swine viruses.

As a result of human-to-pig transmission, pandemic influenza A (H1N1) 2009 virus was detected in pigs soon after it emerged in humans. In the United States, this transmission was quickly followed by multiple reassortment between the pandemic virus and endemic swine viruses. Nine reassortant viruses representing 7 genotypes were detected in commercial pig farms in the United States. Field observations suggested that the newly described reassortant viruses did not differ substantially from pandemic (H1N1) 2009 or endemic strains in their ability to cause disease. Comparable growth properties of reassortant and endemic viruses in vitro supported these observations; similarly, a representative reassortant virus replicated in ferrets to the same extent as did pandemic (H1N1) 2009 and endemic swine virus. These novel reassortant viruses highlight the increasing complexity of influenza viruses within pig populations and the frequency at which viral diversification occurs in this ecologically important viral reservoir.

Transmission of influenza A(H1N1) 2009 pandemic viruses in Australian swine

Please cite this paper as: Deng et al. (2012). Transmission of influenza A(H1N1) 2009 pandemic viruses in Australian swine. Influenza and Other Respiratory Viruses 6(3), e42–e47.

Background  Swine have receptors for both human and avian influenza viruses and are a natural host for influenza A viruses. The 2009 influenza A(H1N1) pandemic (H1N1pdm) virus that was derived from avian, human and swine influenza viruses has infected pigs in various countries.

Objectives  To investigate the relationship between the H1N1pdm viruses isolated from piggery outbreaks in Australia and human samples associated with one of the outbreaks by phylogenetic analysis, and to determine whether there was any reassortment event occurring during the human‐pig interspecies transmission.

Methods  Real‐time RT‐PCR and full genome sequencing were carried out on RNA isolated from nasal swabs and/or virus cultures. Phylogenetic analysis was performed using the Geneious package.

Results  The influenza H1N1pdm outbreaks were detected in three pig farms located in three different states in Australia. Further analysis of the Queensland outbreak led to the identification of two distinct virus strains in the pigs. Two staff working in the same piggery were also infected with the same two strains found in the pigs. Full genome sequence analysis on the viruses isolated from pigs and humans did not identify any reassortment of these H1N1pdm viruses with seasonal or avian influenza A viruses.

Conclusions  This is the first report of swine infected with influenza in Australia and marked the end of the influenza‐free era for the Australian swine industry. Although no reassortment was detected in these cases, the ability of these viruses to cross between pigs and humans highlights the importance of monitoring swine for novel influenza infections.

Emergence and dissemination of a swine H3N2 reassortant influenza virus with 2009 pandemic H1N1 genes in pigs in China

The 2009 pandemic influenza virus (pdm/09) has been frequently introduced to pigs and has reassorted with other swine viruses. Recently, H3N2 reassortants with pdm/09-like internal genes were isolated in Guangxi and Hong Kong, China. Genetic and epidemiological analyses suggest that these viruses have circulated in swine for some time. This is the first evidence that swine reassortant viruses with pdm/09-like genes may have become established in the field, altering the landscape of human and swine influenza.

Transmission of influenza A virus in pigs

Influenza A virus infections cause respiratory disease in pigs and are a risk to public health. The pig plays an important role in influenza ecology because of its ability to support replication of influenza viruses from avian, swine and human species. Influenza A virus is widespread in pigs worldwide, and influenza A virus interspecies transmission has been documented in many events. Influenza A virus is mostly transmitted through direct pig-to-pig contact and aerosols although other indirect routes of transmission may also exist. Several factors contribute to differences in the transmission dynamics within populations including among others vaccination, pig flow, animal movement and animal introduction which highlights the complexity of influenza A transmission in pigs. In addition, pigs can serve as a reservoir of influenza A viruses for other pigs and other species and understanding mechanisms of transmission within pigs and from pigs to other species and vice versa is crucial. In this paper, we review the current understanding of influenza virus transmission in pigs. We highlight the ubiquity of influenza A virus in the pig population and the widespread distribution of pandemic H1N1 virus worldwide while emphasizing an understanding of the routes of transmission and factors that contribute to virus spread and dissemination within and between pig populations. In addition, we describe transmission events between pigs and other species including people. Understanding transmission is crucial for designing effective control strategies and for making well-informed recommendations for surveillance.

Transmission of pandemic influenza H1N1 (2009) in Vietnamese swine in 2009-2010

BACKGROUND

The pandemic of 2009 was caused by an H1N1 (H1N1pdm) virus of swine origin. This pandemic virus has repeatedly infected swine through reverse zoonosis, although the extent of such infection in swine remains unclear.

OBJECTIVE

This study targets small and commercial pig producers in North Vietnam, in order to estimate the extent of H1N1pdm infection in swine and to identify the risk factors of infection.

METHODS

Virologic and serologic surveillance of swine was carried out in 2009-2010 in pig farms (38 swabs and 1732 sera) and at a pig slaughterhouse (710 swabs and 459 sera) in North Vietnam. The sera were screened using a influenza type A-reactive ELISA assay, and positive sera were tested using hemagglutination inhibition tests for antibody to a panel of H1-subtype viruses representing pandemic (H1N1) 2009 (H1N1pdm), triple reassortant (TRIG), classical swine (CS), and Eurasian avian-like (EA) swine lineages. Farm-level risk factors were identified using a zero-inflated negative binomial model.

RESULTS

We found a maximal seroprevalence of H1N1pdm of 55·6% [95% CI: 38·1-72·1] in the slaughterhouse at the end of December 2009, 2 weeks after the peak of reported human fatalities with H1N1pdm. Farm-level seroprevalence was 29% [95% CI: 23·2-35·7]. In seropositive farms, within-herd seroprevalence ranged from 10 to 100%. We identified an increased risk of infection for farms that specialized in fattening and a decreased risk of infection in farms hiring external swine workers.

CONCLUSIONS

Our findings suggest extensive reverse-zoonotic transmission from humans to pigs with subsequent onward transmission within pig herds.

Swine influenza surveillance in East and Southeast Asia: a systematic review

East and Southeast Asia are important pig- and poultry-producing areas, where the majority of production takes place on small-scale farms with low biosecurity levels. This systematic review synthesizes data on swine influenza virology, serology and epidemiology in East and Southeast Asia. A total of 77 research articles, literature reviews and conference papers were selected and analyzed from 510 references retrieved from PubMed and ISI Web of KnowledgeSM. The number of published articles increased in the last 3 years, which may be attributed to improvement in monitoring and/or a better promotion of surveillance data. Nevertheless, large inequalities in surveillance and research among countries are underlined. Virological results represent the largest part of published data, while the serological and epidemiological features of swine influenza in East and Southeast Asia remain poorly described. The literature shows that there have been several emergences of swine influenza in the region, and also considerable evidence of multiple introductions of North American and avian-like European strains. Furthermore, several avian-origin strains are isolated from pigs, including H5 and H9 subtypes. However, their low seroprevalence in swine also shows that pigs remain poorly infected by these subtypes. We conclude that sero-epidemioligical investigations have been neglected, and that they may help to improve virological surveillance. Inter- and intra-continental surveillance of gene flows will benefit the region. Greater investment is needed in swine influenza surveillance, to improve our knowledge of circulating strains as well as the epidemiology and disease burden in the region.

Single-step multiplex reverse transcription polymerase chain reaction assay for detection and differentiation of the 2009 H1N1 Influenza A virus pandemic in Thai swine populations

A recently emerged H1N1 Influenza A virus (pandemic H1N1 (pH1N1)) with a Swine influenza virus (SIV) genetic background spread globally from human-to-human causing the first influenza virus pandemic of the 21st century. In a short period, reverse zoonotic cases in pigs followed by a widespread of the virus in the pig population were documented. The implementation of effective control strategies, rapid diagnosis, and differentiation of such virus from endemically circulating SIV in the various swine populations of the world is needed. To address the problem, a multiplex reverse transcription polymerase chain reaction assay utilizing a combination of the PB1, H1, and N1 primers that can rapidly and simultaneously subtype and screen for the presence of pH1N1 virus infection in Thai pigs was developed. The assay had 100% specificity and did not amplify genetic material from other subtypes of SIV, seasonal H1N1 human influenza (huH1N1) virus, highly pathogenic influenza H5N1 virus, and other important swine respiratory viral pathogens. The assay was able to both detect and subtype pH1N1 virus as low as 0.1-50% tissue culture infective doses/ml (TCID(50)/ml). The assay was used to screen 175 clinical samples obtained from SIV suspected cases, of which 6 samples were pH1N1 positive and were confirmed through virus isolation and whole genome sequencing. The results of the study suggested that the assay would be useful for the rapid diagnosis of pH1N1 in suspected Thai swineherds, where genetics of the endemically circulating SIV differ from the strains circulating in North American and European herds.

2009 pandemic H1N1 influenza virus causes disease and upregulation of genes related to inflammatory and immune responses, cell death, and lipid metabolism in pigs

There exists limited information about whether adaptation is needed for cross-species transmission of the 2009 pandemic H1N1 influenza virus (pH1N1). Here, we compare the pathogenesis of two pH1N1 viruses, one derived from a human patient (A/CA/04/09 [CA09]) and the other from swine (A/swine/Alberta/25/2009 [Alb09]), with that of the 1918-like classical swine influenza virus (A/swine/Iowa/1930 [IA30]) in the pig model. Both pH1N1 isolates induced clinical symptoms such as coughing, sneezing, decreased activity, fever, and labored breathing in challenged pigs, but IA30 virus did not cause any clinical symptoms except fever. Although both the pH1N1 viruses and the IA30 virus caused lung lesions, the pH1N1 viruses were shed from the nasal cavities of challenged pigs whereas the IA30 virus was not. Global gene expression analysis indicated that transcriptional responses of the viruses were distinct. pH1N1-infected pigs had an upregulation of genes related to inflammatory and immune responses at day 3 postinfection that was not seen in the IA30 infection, and expression levels of genes related to cell death and lipid metabolism at day 5 postinfection were markedly different from those of IA30 infection. These results indicate that both pH1N1 isolates are more virulent due in part to differences in the host transcriptional response during acute infection. Our study also indicates that pH1N1 does not need prior adaptation to infect pigs, has a high potential to be maintained in naïve swine populations, and might reassort with currently circulating swine influenza viruses.

Pandemic influenza: a never-ending story

A novel pandemic influenza emerged in 2009, something that hasn't been seen since 1977. The following issues will be introduced and discussed in this review: the history of influenza pandemics, the emergence of the novel pandemic influenza of 2009, epidemics in the southern and northern hemispheres after the recognition of index cases in the United States, mortality, viral characteristics, prevention in the household setting, clinical aspects, diagnosis, treatment and immunization. Some questions have been answered. However, a number of other questions remain. Scientific research must follow up on these unanswered questions.

Isolation and phylogenetic analysis of pandemic H1N1/09 influenza virus from swine in Jiangsu province of China

To investigate whether the 2009 pandemic H1N1 influenza A virus was still being transmitted in swine, a total of 1029 nasal swab samples from healthy swine were collected from January to May 2010 in Jiangsu province of China. Eight H1N1 influenza viruses were isolated and identified, and their full length genomes were sequenced. We found that all eight of the H1N1 viruses shared higher than 98.0% sequence identity with the 2009 pandemic virus A/Jiangsu/1/2009 (JS1). In addition, some of these viruses had D225G (3/8) mutations in the receptor binding sites of the hemagglutinin (HA) protein, indicating enhancement of their binding affinity to the sialic α2, 3Gal receptor. In conclusion, the 2009 pandemic H1N1 influenza A virus has retro-infected swine from humans in mainland China, and significant viral evolution is still ongoing in this species.

Brief report: Molecular characterization of a novel reassorted pandemic H1N1 2009 in Thai pigs

For the past 10 years, endemic swine influenza H1 viruses in Thailand have been characterized as reassortants of swine virus genes from swine influenza viruses (SIV) in US and European pigs. Here the authors report the emergence of a novel reassorted H1N1 (rH1N1) virus consisted of human, avian, and swine virus genes from the pandemic H1N1 2009 (pH1N1) virus with a neuraminidase (NA) gene from a Thai swine H1N1 (ThH1N1) isolate. The rH1N1 virus was detected in nursery pigs during a respiratory disease outbreak in central Thailand in early 2010. The rH1N1 virus was repeatedly isolated from infected pigs, suggesting that it can transmit efficiently among the pig population. The appearance of rH1N1 virus in the field occurred within months of the introduction of pH1N1 virus into the Thai swine population in late 2009. The finding highlights the role of pig in generating newly reassorted influenza A viruses and also the significance of continuing disease surveillance and genetic characterization of SIV in pigs.

High genetic compatibility and increased pathogenicity of reassortants derived from avian H9N2 and pandemic H1N1/2009 influenza viruses

H9N2 influenza viruses have been circulating worldwide in multiple avian species and repeatedly infecting mammals, including pigs and humans, posing a significant threat to public health. The coexistence of H9N2 and pandemic influenza H1N1/2009 viruses in pigs and humans provides an opportunity for these viruses to reassort. To evaluate the potential public risk of the reassortant viruses derived from these viruses, we used reverse genetics to generate 127 H9 reassortants derived from an avian H9N2 and a pandemic H1N1 virus, and evaluated their compatibility, replication ability, and virulence in mice. These hybrid viruses showed high genetic compatibility and more than half replicated to a high titer in vitro. In vivo studies of 73 of 127 reassortants revealed that all viruses were able to infect mice without prior adaptation and 8 reassortants exhibited higher pathogenicity than both parental viruses. All reassortants with higher virulence than parental viruses contained the PA gene from the 2009 pandemic virus, revealing the important role of the PA gene from the H1N1/2009 virus in generating a reassortant virus with high public health risk. Analyses of the polymerase activity of the 16 ribonucleoprotein combinations in vitro suggested that the PA of H1N1/2009 origin also enhanced polymerase activity. Our results indicate that some avian H9-pandemic reassortants could emerge with a potentially higher threat for humans and also highlight the importance of monitoring the H9-pandemic reassortant viruses that may arise, especially those that possess the PA gene of H1N1/2009 origin.