Pathogenesis of swine influenza virus (Thai isolates) in weanling pigs: an experimental trial

<p>Abstract</p> <p>Background</p> <p>The objective of this study is to investigate the pathogenesis of swine influenza virus (SIV) subtype H1N1 and H3N2 (Thai isolates) in 22-day-old SPF pigs.</p> <p>Results</p> <p>The study found that all pigs in the infected groups developed typical signs of flu-like symptoms on 1–4 days post- infection (dpi). The H1N1-infected pigs had greater lung lesion scores than those of the H3N2-infected pigs. Histopathological lesions related to swine influenza-induced lesions consisting of epithelial cells damage, airway plugging and peribronchial and perivascular mononuclear cell infiltration were present in both infected groups. Immunofluorescence and immunohistochemistry using nucleoprotein specific monoclonal antibodies revealed positive staining cells in lung sections of both infected groups at 2 and 4 dpi. Virus shedding was detected at 2 dpi from both infected groups as demonstrated by RT-PCR and virus isolation.</p> <p>Conclusion</p> <p>The results demonstrated that both SIV subtypes were able to induce flu-like symptoms and lung lesions in weanling pigs. However the severity of the diseases with regards to lung lesions both gross and microscopic lesions was greater in the H1N1-infected pigs. Based on phylogenetic analysis, haemagglutinin gene of subtype H1N1 from Thailand clustered with the classical H1 SIV sequences and neuraminidase gene clustered with virus of avian origin, whereas, both genes of H3N2 subtype clustered with H3N2 human-like SIV from the 1970s.</p

Genetic characterization of avian influenza subtype H4N6 and H4N9 from live bird market, Thailand

A one year active surveillance program for influenza A viruses among avian species in a live-bird market (LBM) in Bangkok, Thailand was conducted in 2009. Out of 970 samples collected, influenza A virus subtypes H4N6 (n = 2) and H4N9 (n = 1) were isolated from healthy Muscovy ducks. All three viruses were characterized by whole genome sequencing with subsequent phylogenetic analysis and genetic comparison. Phylogenetic analysis of all eight viral genes showed that the viruses clustered in the Eurasian lineage of influenza A viruses. Genetic analysis showed that H4N6 and H4N9 viruses display low pathogenic avian influenza characteristics. The HA cleavage site and receptor binding sites were conserved and resembled to LPAI viruses. This study is the first to report isolation of H4N6 and H4N9 viruses from birds in LBM in Thailand and shows the genetic diversity of the viruses circulating in the LBM. In addition, co-infection of H4N6 and H4N9 in the same Muscovy duck was observed

Neuraminidase inhibiting antibody responses in pigs differ between influenza A virus N2 lineages and by vaccine type

The neuraminidase (NA) protein of influenza A viruses (IAV) has important functional roles in the viral replication cycle. Antibodies specific to NA can reduce viral replication and limit disease severity, but are not routinely measured. We analyzed NA inhibiting (NI) antibody titers in serum and respiratory specimens of pigs vaccinated with intramuscular whole-inactivated virus (WIV), intranasal live-attenuated influenza virus (LAIV), and intranasal wild type (WT) IAV. NI titers were also analyzed in sera from an investigation of piglet vaccination in the presence of passive maternally-derived antibodies. Test antigens contained genetically divergent swine-lineage NA genes homologous or heterologous to the vaccines with mismatched hemagglutinin genes (HA). Naïve piglets responded to WIV and LAIV vaccines and WT infection with strong homologous serum NI titers. Cross-reactivity to heterologous NAs depended on the degree of genetic divergence between the NA genes. Bronchoalveolar lavage specimens of LAIV and WT-immunized groups also had significant NI titers against the homologous antigen whereas the WIV group did not. Piglets of vaccinated sows received high levels of passive NI antibody, but their NI responses to homologous LAIV vaccination were impeded. These data demonstrate the utility of the enzyme-linked lectin assay for efficient NI antibody titration of serum as well as respiratory tract secretions. Swine IAV vaccines that induce robust NI responses are likely to provide broader protection against the diverse and rapidly evolving IAV strains that circulate in pig populations. Mucosal antibodies to NA may be one of the protective immune mechanisms induced by LAIV vaccines

Genetic variations of nucleoprotein gene of influenza A viruses isolated from swine in Thailand

<p>Abstract</p> <p>Background</p> <p>Influenza A virus causes severe disease in both humans and animals and thus, has a considerably impact on economy and public health. In this study, the genetic variations of the nucleoprotein (NP) gene of influenza viruses recovered from swine in Thailand were determined.</p> <p>Results</p> <p>Twelve influenza A virus specimens were isolated from Thai swine. All samples were subjected to nucleotide sequencing of the complete NP gene. Phylogenetic analysis was conducted by comparing the NP gene of swine influenza viruses with that of seasonal and pandemic human viruses and highly pathogenic avian viruses from Thailand (n = 77). Phylogenetic analysis showed that the NP gene from different host species clustered in distinct host specific lineages. The NP gene of swine influenza viruses clustered in either Eurasian swine or Classical swine lineages. Genetic analysis of the NP gene suggested that swine influenza viruses circulating in Thailand display 4 amino acids unique to Eurasian and Classical swine lineages. In addition, the result showed 1 and 5 amino acids unique to avian and human lineages, respectively. Furthermore, nucleotide substitution rates showed that the NP gene is highly conserved especially in avian influenza viruses.</p> <p>Conclusion</p> <p>The NP gene sequence of influenza A in Thailand is highly conserved within host-specific lineages and shows amino acids potentially unique to distinct NP lineages. This information can be used to investigate potential interspecies transmission of influenza A viruses. In addition, the genetic variations of the NP gene will be useful for monitoring the viruses and preparing effective prevention and control strategies for potentially pandemic influenza outbreaks.</p

Fox Squirrels (Sciurus niger) Develop West Nile Virus Viremias Sufficient for Infecting Select Mosquito Species

The West Nile virus (WNV) viremia and shedding profiles of 11 adult fox squirrels (Sciurus niger) infected by needle inoculation or mosquito bite were characterized. Daily mean titers (95% confidence intervals) for all squirrels on days 1 through 6 postexposure (p.e.) were: 10(1.7 (1.32.1)), 10(4.4 (4.04.8)), 10(5.3 (5.05.6)), 10(4.4 (3.94.9)), 10(2.7 (2.03.4)), and 10(1.1 (0.52.1)) plaque-forming units (PFU)/mL. The highest WNV serum titers of individual squirrels infected by needle inoculation or mosquito bite ranged from 10(4.5) to 10(6.1) and from 10(5.1) to 10(5.3) PFU/mL, respectively. Nine (82%) squirrels, including all 4 squirrels infected by mosquito bite, had WNV serum titers \u3e or =10(5.1) PFU/mL that persisted on average for 1.6 +/- 0.3 days. Infection and dissemination rates of Culex pipiens (L.) that fed on squirrels with serum titers of 10(4.4 +/- 0.1) PFU/mL were 56% and 13%, respectively. Both of these rates increased to over 80% when fed on squirrels with a mean WNV titer of 10(5.5 +/- 0.1) PFU/mL. Infection and dissemination also occurred in Aedes triseriatus (Say) but at a much lower rate. WNV was isolated from the oral and rectal cavities of all squirrels and from urine that was opportunistically collected from 5 squirrels. The largest quantity of WNV recovered from swabs of the oral cavity and urine was 10(3.1) PFU. The longest periods after exposure that WNV was isolated from the oral cavity and urine from a squirrel were 22 and 17 days p.e., respectively. WNV RNA was also detected in kidney tissue in 1 squirrel 29 days p.e., suggesting that fox squirrels can be persistently infected. Collectively these observations provide further evidence that squirrels can contribute to the natural history and epidemiology of WNV, especially in peridomestic environments

Efficacy in Pigs of Inactivated and Live Attenuated Influenza Virus Vaccines against Infection and Transmission of an Emerging H3N2 Similar to the 2011-2012 H3N2v

Vaccines provide a primary means to limit disease but may not be effective at blocking infection and pathogen transmission. The objective of the present study was to evaluate the efficacy of commercial inactivated swine influenza A virus (IAV) vaccines and experimental live attenuated influenza virus (LAIV) vaccines against infection with H3N2 virus and subsequent indirect transmission to naive pigs. The H3N2 virus evaluated was similar to the H3N2v detected in humans during 2011-2012, which was associated with swine contact at agricultural fairs. One commercial vaccine provided partial protection measured by reduced nasal shedding; however, indirect contacts became infected, indicating that the reduction in nasal shedding did not prevent aerosol transmission. One LAIV vaccine provided complete protection, and none of the indirect-contact pigs became infected. Clinical disease was not observed in any group, including nonvaccinated animals, a consistent observation in pigs infected with contemporary reassortant H3N2 swine viruses. Serum hemagglutination inhibition antibody titers against the challenge virus were not predictive of efficacy; titers following vaccination with a LAIV that provided sterilizing immunity were below the level considered protective, yet titers in a commercial vaccine group that was not protected were above that level. While vaccination with currently approved commercial inactivated products did not fully prevent transmission, certain vaccines may provide a benefit by limitating shedding, transmission, and zoonotic spillover of antigenically similar H3N2 viruses at agriculture fairs when administered appropriately and used in conjunction with additional control measures

Chinese-like Strain of Porcine Epidemic Diarrhea Virus, Thailand

Since late 2007, several outbreaks of porcine epidemic diarrhea virus (PEDV) infection have emerged in Thailand. Phylogenetic analysis places all Thai PEDV isolates during the outbreaks in the same clade as the Chinese strain JS-2004-2. This new genotype PEDV is prevailing and currently causing sporadic outbreaks in Thailand

Pandemic (H1N1) 2009 Virus on Commercial Swine Farm, Thailand

A swine influenza outbreak occurred on a commercial pig farm in Thailand. Outbreak investigation indicated that pigs were co-infected with pandemic (H1N1) 2009 virus and seasonal influenza (H1N1) viruses. No evidence of gene reassortment or pig-to-human transmission of pandemic (H1N1) 2009 virus was found during the outbreak