Bovine Rhinitis B Virus Variant as the Putative Cause of Bronchitis in Goat Kids.

A diagnostic investigation into an outbreak of fatal respiratory disease among young goats in Iowa, USA revealed bronchitis lesions of unknown etiology and secondary bacterial bronchopneumonia. Hypothesis-free metagenomics identified a previously unreported picornavirus (USA/IA26017/2023), and further phylogenetic analysis classified USA/IA26017/2023 as an aphthovirus related to bovine rhinitis B virus. Viral nucleic acid was localized to lesions of bronchitis using in situ hybridization. This marks the first report of a picornavirus putatively causing respiratory disease in goats and highlights the potential for cross-species transmission of aphthoviruses.

Diagnostic investigation of Mycoplasma hyorhinis as a potential pathogen associated with neurological clinical signs and central nervous system lesions in pigs.

Mycoplasma hyorhinis (M. hyorhinis) is a commensal of the upper respiratory tract in swine with the typical clinical presentations of arthritis and polyserositis in postweaning pigs. However, it has also been associated with conjunctivitis and otitis media, and recently has been isolated from meningeal swabs and/or cerebrospinal fluid of piglets with neurological signs. The objective of this study is to evaluate the role of M. hyorhinis as a potential pathogen associated with neurological clinical signs and central nervous system lesions in pigs. The presence of M. hyorhinis was evaluated in a clinical outbreak and a six-year retrospective study by qPCR detection, bacteriological culture, in situ hybridization (RNAscope®), and phylogenetic analysis and with immunohistochemistry characterization of the inflammatory response associated with its infection. M. hyorhinis was confirmed by bacteriological culture and within central nervous system lesions by in situ hybridization on animals with neurological signs during the clinical outbreak. The isolates from the brain had close genetic similarities from those previously reported and isolated from eye, lung, or fibrin. Nevertheless, the retrospective study confirmed by qPCR the presence of M. hyorhinis in 9.9% of cases reported with neurological clinical signs and histological lesions of encephalitis or meningoencephalitis of unknown etiology. M. hyorhinis mRNA was confirmed within cerebrum, cerebellum, and choroid plexus lesions by in situ hybridization (RNAscope®) with a positive rate of 72.7%. Here we present strong evidence that M. hyorhinis should be included as a differential etiology in pigs with neurological signs and central nervous system inflammatory lesions.

Genetic characterization of porcine sapoviruses identified from pigs during a diarrhoea outbreak in Iowa, 2019.

Porcine sapovirus (SaV) was first identified by electron microscopy in the United States in 1980 and has since been reported from both asymptomatic and diarrhoeic pigs usually in mixed infection with other enteric pathogens. SaV as the sole aetiological agent of diarrhoea in naturally infected pigs has not previously been reported in the United States. Here, we used four independent lines of evidence including metagenomics analysis, real-time RT-PCR (rRT-PCR), histopathology, and in situ hybridization to confirm porcine SaV genogroup III (GIII) as the sole cause of enteritis and diarrhoea in pigs. A highly sensitive and specific rRT-PCR was established to detect porcine SaV GIII. Examination of 184 faecal samples from an outbreak of diarrhoea on a pig farm showed that pigs with clinical diarrhoea had significantly lower Ct values (15.9 ± 0.59) compared to clinically unaffected pigs (35.8 ± 0.71). Further survey of 336 faecal samples from different states in the United States demonstrated that samples from pigs with clinical diarrhoea had a comparable positive rate (45.3%) with those from asymptomatic pigs (43.1%). However, the SaV-positive pigs with clinical diarrhoea had significantly higher viral loads (Ct  = 26.0 ± 0.5) than the SAV-positive but clinically healthy pigs (Ct  = 33.2 ± 0.9). Phylogenetic analysis of 20 field SaVs revealed that all belonged to SaV GIII and recombination analysis indicated that intragenogroup recombination had occurred within the field isolates of SaV GIII. These results suggest that porcine SaV GIII plays an important aetiologic role in swine enteritis and diarrhoea and rRT-PCR is a reliable method to detect porcine SaV. Our findings provide significant insights to better understand the epidemiology and pathogenicity of porcine SaV infection.

Novel Morbillivirus as Putative Cause of Fetal Death and Encephalitis among Swine.

Morbilliviruses are highly contagious pathogens. The Morbillivirus genus includes measles virus, canine distemper virus (CDV), phocine distemper virus (PDV), peste des petits ruminants virus, rinderpest virus, and feline morbillivirus. We detected a novel porcine morbillivirus (PoMV) as a putative cause of fetal death, encephalitis, and placentitis among swine by using histopathology, metagenomic sequencing, and in situ hybridization. Phylogenetic analyses showed PoMV is most closely related to CDV (62.9% nt identities) and PDV (62.8% nt identities). We observed intranuclear inclusions in neurons and glial cells of swine fetuses with encephalitis. Cellular tropism is similar to other morbilliviruses, and PoMV viral RNA was detected in neurons, respiratory epithelium, and lymphocytes. This study provides fundamental knowledge concerning the pathology, genome composition, transmission, and cellular tropism of a novel pathogen within the genus Morbillivirus and opens the door to a new, applicable disease model to drive research forward.

Porcine Hemagglutinating Encephalomyelitis Virus Infection In Vivo and Ex Vivo.

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a betacoronavirus that causes vomiting and wasting disease and/or encephalomyelitis in suckling pigs. This study characterized PHEV infection, pathogenesis, and immune response in cesarean-derived, colostrum-deprived (CDCD) neonatal pigs. Infected animals developed mild respiratory, enteric, and neurological clinical signs between 2 to 13 days postoronasal inoculation (dpi). PHEV did not produce viremia, but virus shedding was detected in nasal secretions (1 to 10 dpi) and feces (2 to 7 dpi) by reverse transcriptase quantitative PCR (RT-qPCR). Viral RNA was detected in all tissues except liver, but the detection rate and RT-qPCR threshold cycle (CT ) values decreased over time. The highest concentration of virus was detected in inoculated piglets necropsied at 5 dpi in turbinate and trachea, followed by tonsils, lungs, tracheobronchial lymph nodes, and stomach. The most representative microscopic lesions were gastritis lymphoplasmacytic, moderate, multifocal, with perivasculitis, and neuritis with ganglia degeneration. A moderate inflammatory response, characterized by increased levels of interferon alpha (IFN-α) in plasma (5 dpi) and infiltration of T lymphocytes and macrophages were also observed. Increased plasma levels of interleukin-8 (IL-8) were detected at 10 and 15 dpi, coinciding with the progressive resolution of the infection. Moreover, a robust antibody response was detected by 10 dpi. An ex vivo air-liquid CDCD-derived porcine respiratory cells culture (ALI-PRECs) system showed virus replication in ALI-PRECs and cytopathic changes and disruption of ciliated columnar epithelia, thereby confirming the tracheal epithelia as a primary site of infection for PHEV.IMPORTANCE Among the ∼46 virus species in the family Coronaviridae, many of which are important pathogens of humans and 6 of which are commonly found in pigs, porcine hemagglutinating encephalomyelitis remains one of the least researched. The present study provided a comprehensive characterization of the PHEV infection process and immune responses using CDCD neonatal pigs. Moreover, we used an ex vivo ALI-PRECs system resembling the epithelial lining of the tracheobronchial region of the porcine respiratory tract to demonstrate that the upper respiratory tract is a primary site of PHEV infection. This study provides a platform for further multidisciplinary studies of coronavirus infections.

Case Report and Genomic Characterization of a Novel Porcine Nodavirus in the United States.

Nodaviruses are small bisegmented RNA viruses belonging to the family Nodaviridae. Nodaviruses have been identified in different hosts, including insects, fishes, shrimps, prawns, dogs, and bats. A novel porcine nodavirus was first identified in the United States by applying next-generation sequencing on brain tissues of pigs with neurological signs, including uncontrollable shaking. RNA1 of the porcine nodavirus had the highest nucleotide identity (51.1%) to the Flock House virus, whereas its RNA2 shared the highest nucleotide identity (48%) with the RNA2 segment of caninovirus (Canine nodavirus). Genetic characterization classified porcine nodavirus as a new species under the genus Alphanodavirus. Further studies are needed to understand the pathogenicity and clinical impacts of this virus.

Role of enterotoxigenic Escherichia coli prophage in spreading antibiotic resistance in a porcine-derived environment.

Enterotoxigenic Escherichia coli (ETEC) cause acute secretory diarrhoea in pigs, posing a great economic loss to the swine industry. This study analysed the prevalence and genetic characteristics of prophages from 132 ETEC isolates from symptomatic pigs to determine their potential for spreading antibiotic resistance. A total of 1105 potential prophages were identified, and the distribution of the genome size showed three 'overlapping' trends. Similarity matrix comparison showed that prophages correlated with the ETEC lineage distribution, and further identification of these prophages corroborated the lineage specificity. In total, 1206 antibiotic resistance genes (ARGs) of 52 different categories were identified in 132 ETEC strains; among these, 2.65% (32/1206) of ARGs were found to be carried by prophages. Analysis of flanking sequences showed that almost all the ARGs could be grouped into two types: 'blaTEM-1B ' and 'classic class 1 integron (IntI1)'. They co-occurred with a strictly conserved recombinase and transposon Tn3 family but with a difference: the 'blaTEM-1B type' prophages exhibited a classic Tn2 transposon structure with 100% sequence identity, whereas the 'IntI1 type' co-occurred with the TnAs2 transposon with only 84% sequence identity. These results imply that ARGs might be pervasive in natural bacterial populations through transmission by transposable bacteriophages.

Isolation of PCV3 from Perinatal and Reproductive Cases of PCV3-Associated Disease and In Vivo Characterization of PCV3 Replication in CD/CD Growing Pigs.

Porcine circovirus 3 (PCV3) has been identified as a putative swine pathogen with a subset of infections resulting in stillborn and mummified fetuses, encephalitis and myocarditis in perinatal, and periarteritis in growing pigs. Three PCV3 isolates were isolated from weak-born piglets or elevated stillborn and mummified fetuses. Full-length genome sequences from different passages and isolates (PCV3a1 ISU27734, PCV3a2 ISU58312, PCV3c ISU44806) were determined using metagenomics sequencing. Virus production in cell culture was confirmed by qPCR, IFA, and in situ hybridization. In vivo replication of PCV3 was also demonstrated in CD/CD pigs (n = 8) under experimental conditions. Viremia, first detected at 7 dpi, was detected in all pigs by 28 dpi. IgM antibody response was detected between 7-14 dpi in 5/8 PCV3-inoculated pigs but no IgG seroconversion was detected throughout the study. Pigs presented histological lesion consistent with multi systemic inflammation characterized by myocarditis and systemic perivasculitis. Viral replication was confirmed in all tissues by in situ hybridization. Clinically, all animals were unremarkable throughout the study. Although the clinical relevance of PCV3 remains under debate, this is the first isolation of PCV3 from perinatal and reproductive cases of PCV3-associated disease and in vivo characterization of PCV3 infection in a CD/CD pig model.

Astrovirus in White-Tailed Deer, United States, 2018.

We report the identification of astrovirus WI65268 in a white-tailed deer with respiratory disease in the United States in 2018. This virus is a recombinant of Kagoshima1-7 and Kagoshima2-3-2 (both bovine astroviruses from Japan) and was characterized as a potential new genotype. Further surveillance of deer might help identify related isolates.

Genetic diversity of porcine reproductive and respiratory syndrome virus 1 in the United States of America from 2010 to 2018.

Porcine reproductive and respiratory syndrome virus 1 (PRRSV-1) was first detected in the United States of America (USA) in 1999, several strains were also recognized soon later, and these isolates are typically called North American (NA) PRRSV-1. However, few reports have characterized PRRSV-1 viruses in the USA. We explored the genetic characteristics and diversity of PRRSV-1 viruses circulating in the USA. PRRSV-1 PCR-positive samples collected from seven states in 2010-2018 (n = 27) were subjected to next-generation sequencing. The 27 PRRSV-1 viruses had 88.4-91.3% nucleotide identity to the PRRSV-1 Lelystad-virus strain (the type 1 prototype strain) and 87.4-89.8% to the previously reported NA PRRSV-1 viruses. Individual proteins had several unique genetic characteristics and only one of the 27 tested samples had the characteristic 17-amino acid (aa) deletion in Nsp2, a genetic marker of NA PRRSV-1 viruses described previously. Fourteen isolates displayed a 3-aa C-terminal truncation in the highly conserved Nsp12 gene; 16 samples had a 21- or 18-aa C-terminal truncation in GP3 gene; and one was observed with a 1-aa deletion at the overlapping region of GP3 and GP4. In addition, the GP5 protein in most isolates, excluding one exception, demonstrated similar genetic variation as other reported NA PRRSV-1 isolates. All tested isolates clustered within subtype 1 together with other available NA PRRSV-1 viruses. Collectively, our results provide up-to-date information on PRRSV-1 viruses circulating in the USA in the past 9 years although the number of PRRSV-1 isolates included in this study is limited. These PRRSV-1 viruses have undergone gradual genetic variation and exhibited some previously undescribed genetic characteristics and diversity, which complicates the diagnosis and control of NA PRRSV-1.

Virus survival and fitness when multiple genotypes and subtypes of influenza A viruses exist and circulate in swine.

We performed swine influenza virus (SIV) surveillance in Midwest USA and isolated 100 SIVs including endemic and reassortant H1 and H3 viruses with 2009 pandemic H1N1 genes. To determine virus evolution when different genotypes and subtypes of influenza A viruses circulating in the same swine herd, a virus survival experiment was conducted in pigs mimicking field situations. Five different SIVs were used to infect five pigs individually, then two groups of sentinel pigs were introduced to investigate virus transmission. Results showed that each virus replicated efficiently in lungs of each infected pig, but only reassortant H3N2 and H1N2v viruses transmitted to the primary contact pigs. Interestingly, the parental H1N2v was the majority of virus detected in the second group of sentinel pigs. These data indicate that the H1N2v seems to be more viable in swine herds than other SIV genotypes, and reassortment can enhance viral fitness and transmission.

Genomic Sequence of a Megrivirus Strain Identified in Laying Hens in Brazil.

A new strain of chicken megrivirus was identified in fecal samples of layer chickens in a commercial flock in Minas Gerais, Brazil. It is most closely related to the family Picornaviridae, genus Megrivirus, species Melegrivirus A, and has an overall nucleotide identity of up to 85.1% with other megrivirus strains.

Detection and genomic characterization of new avian-like hepatitis E virus in a sparrow in the United States.

Hepatitis E virus (HEV) is a nonenveloped, positive-sense, single-stranded RNA virus that has been detected in a wide variety of animals. In 2017, an avian-like HEV was identified in sparrow feces sampled from around a pig farm in the midwestern United States. Sequence analysis revealed that the sparrow isolate represents a novel HEV that is distantly related to chicken and little egret HEVs.

Genomic Sequence of a Swine Pasivirus Type 1 Strain Identified in U.S. Swine.

We report for the first time in the United States the identification of a swine pasivirus (SPaV) strain with a genomic sequence identity of less than 80% to other SPaVs reported in Europe and China, using a next-generation sequencing (NGS) technique in sow tissues collected from an animal study conducted in 2001, suggesting virus circulation in domestic swine.

Comparison of the efficacy of a commercial inactivated influenza A/H1N1/pdm09 virus (pH1N1) vaccine and two experimental M2e-based vaccines against pH1N1 challenge in the growing pig model.

Swine influenza A viruses (IAV-S) found in North American pigs are diverse and the lack of cross-protection among heterologous strains is a concern. The objective of this study was to compare a commercial inactivated A/H1N1/pdm09 (pH1N1) vaccine and two novel subunit vaccines, using IAV M2 ectodomain (M2e) epitopes as antigens, in a growing pig model. Thirty-nine 2-week-old IAV negative pigs were randomly assigned to five groups and rooms. At 3 weeks of age and again at 5 weeks of age, pigs were vaccinated intranasally with an experimental subunit particle vaccine (NvParticle/M2e) or a subunit complex-based vaccine (NvComplex/M2e) or intramuscularly with a commercial inactivated vaccine (Inact/pH1N1). At 7 weeks of age, the pigs were challenged with pH1N1 virus or sham-inoculated. Necropsy was conducted 5 days post pH1N1 challenge (dpc). At the time of challenge one of the Inact/pH1N1 pigs had seroconverted based on IAV nucleoprotein-based ELISA, Inact/pH1N1 pigs had significantly higher pdm09H1N1 hemagglutination inhibition (HI) titers compared to all other groups, and M2e-specific IgG responses were detected in the NvParticle/M2e and the NvComplex/M2e pigs with significantly higher group means in the NvComplex/M2e group compared to SHAMVAC-NEG pigs. After challenge, nasal IAV RNA shedding was significantly reduced in Inact/pH1N1 pigs compared to all other pH1N1 infected groups and this group also had reduced IAV RNA in oral fluids. The macroscopic lung lesions were characterized by mild-to-severe, multifocal-to-diffuse, cranioventral dark purple consolidated areas typical of IAV infection and were similar for NvParticle/M2e, NvComplex/M2e and SHAMVAC-IAV pigs. Lesions were significantly less severe in the SHAMVAC-NEG and the Inact/pH1N1pigs. Under the conditions of this study, a commercial Inact/pH1N1 specific vaccine effectively protected pigs against homologous challenge as evidenced by reduced clinical signs, virus shedding in nasal secretions and oral fluids and reduced macroscopic and microscopic lesions whereas intranasal vaccination with experimental M2e epitope-based subunit vaccines did not. The results further highlight the importance using IAV-S type specific vaccines in pigs.

Evaluation of the efficacy of a commercial inactivated genogroup 2b-based porcine epidemic diarrhea virus (PEDV) vaccine and experimental live genogroup 1b exposure against 2b challenge.

Porcine epidemic diarrhea virus strains from the G1b cluster are considered less pathogenic compared to the G2b cluster. The aim of this study was to compare the ability of G1b-based live virus exposure against use of a commercial G2b-based inactivated vaccine to protect growing pigs against G2b challenge. Thirty-nine PEDV naïve pigs were randomly divided into five groups: EXP-IM-1b (intramuscular G1b exposure; G2b challenge), EXP-ORAL-1b (oral G1b exposure; G2b challenge), VAC-IM-2b (intramuscular commercial inactivated G2b vaccination; G2b challenge), POS-CONTROL (sham-vaccination; G2b challenge) and NEG-CONTROL (sham-vaccination; sham-challenge). Pigs were vaccinated/exposed at 3 weeks of age (day post-vaccination 0, dpv 0), VAC-IM-2b pigs were revaccinated at dpv 14, and the pigs were challenged at dpv 28. Among all groups, VAC-IM-2b pigs had significantly higher anti-PEDV IgG levels on dpv 21 and 28 while EXP-ORAL-1b pigs had significantly higher anti-PEDV IgA levels on dpv 14, 21, 28 and 35. EXP-ORAL-1b also had detectable IgA in feces. Intramuscular PEDV exposure did not result in a detectable antibody response in EXP-IM-1b pigs. The fecal PEDV RNA levels in VAC-IM-2b pigs were significantly lower 5-7 days after challenge compared to the POS-CONTROL group. Under the study conditions a commercial inactivated G2b-based vaccine protected pigs against G2b challenge, as evidenced by reduction of PEDV RNA in feces for 3-4 logs during peak shedding and a shorter viral shedding duration. The oral, but not the intramuscular, experimental G1b-based live virus exposure induced a high anti-PEDV IgA response prior to challenge, which apparently did not impact PEDV shedding compared to POS-CONTROL pigs.

An interferon inducing porcine reproductive and respiratory syndrome virus vaccine candidate elicits protection against challenge with the heterologous virulent type 2 strain VR-2385 in pigs.

Achieving consistent protection by vaccinating pigs against porcine reproductive and respiratory syndrome virus (PRRSV) remains difficult. Recently, an interferon-inducing PRRSV vaccine candidate strain A2MC2 was demonstrated to be attenuated and induced neutralizing antibodies. The objective of this study was to determine the efficacy of passage 90 of A2MC2 (A2P90) to protect pigs against challenge with moderately virulent PRRSV strain VR-2385 (92.3% nucleic acid identity with A2MC2) and highly virulent atypical PRRSV MN184 (84.5% nucleic acid identity with A2MC2). Forty 3-week old pigs were randomly assigned to five groups including a NEG-CONTROL group (non-vaccinated, non-challenged), VAC-VR2385 (vaccinated, challenged with strain VR-2385), VR2385 (challenged with strain VR-2385), VAC-MN184 (vaccinated, challenged with strain MN184) and a MN184 group (challenged with MN184 virus). Vaccination was done at 3weeks of age followed by challenge at 8weeks of age. No viremia was detectable in any of the vaccinated pigs; however, by the time of challenge, 15/16 vaccinated pigs had seroconverted based on ELISA and had neutralizing antibodies against a homologous strain with titers ranging from 8 to 128. Infection with VR-2385 resulted in mild-to-moderate clinical disease and lesions. For VR-2385 infected pigs, vaccination significantly lowered PRRSV viremia and nasal shedding by 9days post challenge (dpc), significantly reduced macroscopic lung lesions, and significantly increased the average daily weight gain compared to the non-vaccinated pigs. Infection with MN184 resulted in moderate-to-severe clinical disease and lesions regardless of vaccination status; however, vaccinated pigs had significantly less nasal shedding by dpc 5 compared to non-vaccinated pigs. Under the study conditions, the A2P90 vaccine strain was attenuated without detectable shedding, improved weight gain, and offered protection to the pigs challenged with VR-2385 by reduction of virus load and macroscopic lung lesions. Further work is needed to investigate different vaccination and challenge protocols, including routes, doses, timing and strains.

Domestic pigs are susceptible to infection with influenza B viruses.

UNLABELLED: Influenza B virus (IBV) causes seasonal epidemics in humans. Although IBV has been isolated from seals, humans are considered the primary host and reservoir of this important pathogen. It is unclear whether other animal species can support the replication of IBV and serve as a reservoir. Swine are naturally infected with both influenza A and C viruses. To determine the susceptibility of pigs to IBV infection, we conducted a serological survey for U.S. Midwest domestic swine herds from 2010 to 2012. Results of this study showed that antibodies to IBVs were detected in 38.5% (20/52) of sampled farms, and 7.3% (41/560) of tested swine serum samples were positive for IBV antibodies. Furthermore, swine herds infected with porcine reproductive and respiratory syndrome virus (PRRSV) showed a higher prevalence of IBV antibodies in our 2014 survey. In addition, IBV was detected in 3 nasal swabs collected from PRRSV-seropositive pigs by real-time RT-PCR and sequencing. Finally, an experimental infection in pigs, via intranasal and intratracheal routes, was performed using one representative virus from each of the two genetically and antigenically distinct lineages of IBVs: B/Brisbane/60/2008 (Victoria lineage) and B/Yamagata/16/1988 (Yamagata lineage). Pigs developed influenza-like symptoms and lung lesions, and they seroconverted after virus inoculation. Pigs infected with B/Brisbane/60/2008 virus successfully transmitted the virus to sentinel animals. Taken together, our data demonstrate that pigs are susceptible to IBV infection; therefore, they warrant further surveillance and investigation of swine as a potential host for human IBV. IMPORTANCE: IBV is an important human pathogen, but its ability to infect other species, for example, pigs, is not well understood. We showed serological evidence that antibodies to two genetically and antigenically distinct lineages of IBVs were present among domestic pigs, especially in swine herds previously infected with PRRSV, an immunosuppressive virus. IBV was detected in 3 nasal swabs from PRRSV-seropositive pigs by real-time reverse transcription-PCR and sequencing. Moreover, both lineages of IBV were able to infect pigs under experimental conditions, with transmissibility of influenza B/Victoria lineage virus among pigs being observed. Our results demonstrate that pigs are susceptible to IBV infections, indicating that IBV is a swine pathogen, and swine may serve as a natural reservoir of IBVs. In addition, pigs may serve as a model to study the mechanisms of transmission and pathogenesis of IBVs.

Pathogenicity and transmissibility of novel reassortant H3N2 influenza viruses with 2009 pandemic H1N1 genes in pigs.

UNLABELLED: At least 10 different genotypes of novel reassortant H3N2 influenza viruses with 2009 pandemic H1N1 [A(H1N1)pdm09] gene(s) have been identified in U.S. pigs, including the H3N2 variant with a single A(H1N1)pdm09 M gene, which has infected more than 300 people. To date, only three genotypes of these viruses have been evaluated in animal models, and the pathogenicity and transmissibility of the other seven genotype viruses remain unknown. Here, we show that three H3N2 reassortant viruses that contain 3 (NP, M, and NS) or 5 (PA, PB2, NP, M, and NS) genes from A(H1N1)pdm09 were pathogenic in pigs, similar to the endemic H3N2 swine virus. However, the reassortant H3N2 virus with 3 A(H1N1)pdm09 genes and a recent human influenza virus N2 gene was transmitted most efficiently among pigs, whereas the reassortant H3N2 virus with 5 A(H1N1)pdm09 genes was transmitted less efficiently than the endemic H3N2 virus. Interestingly, the polymerase complex of reassortant H3N2 virus with 5 A(H1N1)pdm09 genes showed significantly higher polymerase activity than those of endemic and reassortant H3N2 viruses with 3 A(H1N1)pdm09 genes. Further studies showed that an avian-like glycine at position 228 at the hemagglutinin (HA) receptor binding site is responsible for inefficient transmission of the reassortant H3N2 virus with 5 A(H1N1)pdm09 genes. Taken together, our results provide insights into the pathogenicity and transmissibility of novel reassortant H3N2 viruses in pigs and suggest that a mammalian-like serine at position 228 in the HA is critical for the transmissibility of these reassortant H3N2 viruses. IMPORTANCE: Swine influenza is a highly contagious zoonotic disease that threatens animal and public health. Introduction of 2009 pandemic H1N1 virus [A(H1N1)pdm09] into swine herds has resulted in novel reassortant influenza viruses in swine, including H3N2 and H1N2 variants that have caused human infections in the United States. We showed that reassortant H3N2 influenza viruses with 3 or 5 genes from A(H1N1)pdm09 isolated from diseased pigs are pathogenic and transmissible in pigs, but the reassortant H3N2 virus with 5 A(H1N1)pdm09 genes displayed less efficient transmissibility than the endemic and reassortant H3N2 viruses with 3 A(H1N1)pdm09 genes. Further studies revealed that an avian-like glycine at the HA 228 receptor binding site of the reassortant H3N2 virus with 5 A(H1N1)pdm09 genes is responsible for less efficient transmissibility in pigs. Our results provide insights into viral pathogenesis and the transmission of novel reassortant H3N2 viruses that are circulating in U.S. swine herds and warrant future surveillance.

Association of concurrent porcine circovirus (PCV) 2a and 2b infection with PCV associated disease in vaccinated pigs.

Investigations were performed to characterize porcine circovirus (PCV) 2 infection in 10 week old pigs from a case of apparent vaccine failure. Thirty serum samples were collected from affected or non-affected pigs and tested for anti-PCV2 antibodies and PCV2 DNA. To address potential PCV2 vaccine compliance issues, samples were tested for antibodies against baculovirus and Mycoplasma hyopneumoniae antigens present in the PCV2 vaccine utilized in this herd. Both PCV2a and PCV2b DNA were detected in 76.6% (90% positive for PCV2a, 86.6% positive for PCV2b), anti-PCV2 IgG in 90%, anti-baculovirus IgG in 50%, and anti-M. hyopneumoniae IgG in 43.3% of the samples. Frequency of baculovirus and M. hyopneumoniae seropositive pigs was significantly lower in affected pigs. The finding that only 50% of the pigs developed a detectable immune response to vaccination suggests poor vaccine compliance or efficacy. Concurrent PCV2a and PCV2b infection was common and may have resulted in enhanced PCV2 replication.