An experimental universal swine influenza a virus (IAV) vaccine candidate based on the M2 ectodomain (M2e) peptide does not provide protection against H1N1 IAV challenge in pigs.

Swine flu is a common disease problem in North American pig populations and swine influenza A viruses (IAV) are extremely diverse and the lack of cross protection between heterologous strains is impacting vaccine efficacy in the field. The objective of this study was to design and test a novel swine flu vaccine targeting the M2 ectodomain (M2e) of IAV, a highly conserved region within the IAV proteome. In brief, an M2e peptide was designed to match the predominant swine IAV M2 sequence based on global analysis of sequences from pigs and humans. The resulting sequence was used to synthesize the M2e peptide coupled to a carrier protein. The final vaccine concentration was 200 µg per dose, and a commercial, microemulsion-based aqueous adjuvant was added. Nine 3-week-old IAV negative piglets were randomly assigned to three groups and rooms including non-vaccinated pigs (NEG-CONTROLs) and vaccinated pigs using the intramuscular (M2e-IM) or the intranasal route (M2e-IN). Vaccinations were done at weaning and again at 2 weeks later. An in-house enzyme-linked immunosorbent assay (ELISA) was developed and validated to study the M2e IgG antibody response and demonstrated M2e-IM pigs had a higher systemic antibody response compared to M2e-IN pigs. Subsequently, an IAV challenge study was conducted. The results indicated that M2e-IM vaccinated pigs were not protected from H1N1 (US pandemic clade, global clade 1A.3.3.2) challenge despite having a strong humoral anti-M2e immune response. In conclusion, while the experimental IAV vaccine was able to induce anti-M2e antibodies, when challenged with H1N1, the vaccinated pigs were not protected, perhaps indicating that reactivity to the M2e antigen alone is not sufficient to reduce clinical signs, lesions or shedding associated with experimental IAV challenge.

Failure to experimentally infect 10 days-old piglets with a cell culture-propagated infectious stock of a classical genotype 1a porcine epidemic diarrhea virus.

Introduction: Porcine epidemic diarrhea virus (PEDV) causes enteric disease in pigs of all ages. PEDV can be grouped into G1 (classical strains) and G2 (variant strains) based on sequence differences in the spike gene. Although several pathogenesis studies using contemporary strains of PEDV have been conducted to date, there is limited information on the pathogenesis of historical PEDV strains in contemporary pigs. This study aimed to investigate the clinical disease course of 10 days-old pigs infected with a classical European G1a PEDV strain from the 1980s which was last passaged in pigs in 1994. Methods: Sequencing results confirmed that the virus inoculum was a PEDV strain closely related to the prototype CV777 strain. The PEDV stock was serially passaged three times in Vero cells, and the P3 infectious virus stock was used to inoculate the pigs. A total of 40 pigs were inoculated using the oral route. Results: Pigs showed no enteric disease signs, and PEDV shedding was not detected for 44 days post-inoculation (dpi). At necropsy at 3 (5 pigs) or 7 dpi (5 pigs), no lesions were observed in intestinal sections, which were negative for PEDV antigen by immunohistochemistry. In addition, no IgG or IgA PEDV-specific antibodies in serum or fecal samples for 35 dpi further indicates a lack of infection. Titration of the leftover thawed and refrozen PEDV virus stock inoculum showed that the virus stock retained its infectivity in Vero cell culture and the porcine small intestine enterocytes cell line IPEC-J2. Discussion: The reasons for the loss of infectivity in pigs are unknown. In conclusion, we showed that a classical G1a PEDV strain successfully propagated in cell cultures could not orally infect 40 piglets.

Porcine Respiratory Coronavirus (PRCV): Isolation and Characterization of a Variant PRCV from USA Pigs.

Porcine respiratory coronavirus (PRCV), a mutant of the transmissible gastroenteritis virus (TGEV), was first reported in Belgium in 1984. PRCV typically replicates and induces mild lesions in the respiratory tract, distinct from the enteric tropism of TGEV. In the past 30 years, PRCV has rarely been studied, and most cited information is on traditional isolates obtained during the 1980s and 1990s. Little is known about the genetic makeup and pathogenicity of recent PRCV isolates. The objective of this study was to obtain a contemporary PRCV isolate from US pigs for genetic characterization. In total, 1245 lung homogenate samples from pigs in various US states were tested via real-time PCR targeting PRCV and TGEV RNA. Overall, PRCV RNA was detected in five samples, and a single isolate (ISU20-92330) was successfully cultured and sequenced for its full-length genome. The isolate clustered with a new group of variant TGEVs and differed in various genomic regions compared to traditional PRCV isolates. Pathogens, such as PRCV, commonly circulate in pig herds without causing major disease. There may be value in tracking genomic changes and regularly updating the diagnostic methods for such viruses to be better prepared for the emergence of variants in ecology and pathogenicity.

Experimental Infection of Pigs with a Traditional or a Variant Porcine Respiratory Coronavirus (PRCV) Strain and Impact on Subsequent Influenza A Infection.

Porcine respiratory coronavirus (PRCV) pathogenicity in pigs has been characterized using traditional PRCV isolates; however, information is lacking on pathogenicity of currently circulating PRCV isolates. Recently, a contemporary US PRCV variant was isolated. The infection dynamics of that strain (PRCV-var) and a traditional PRCV strain (PRCV-trad) were compared. In brief, 4-week-old pigs were divided into three groups with five pigs each. The pigs were inoculated with PRCV-trad or PRCV-var, or left uninfected. Nasal swabs were collected daily, and all pigs were necropsied at day (D) 3. PRCV nasal shedding was significantly higher in PRCV-var pigs compared to PRCV-trad pigs. To investigate the impact of trad and var PRCVs on subsequent infection with influenza A virus (IAV), four additional groups of five pigs were used: PRCV-trad-IAV (PRCV-trad at D0, co-infected with IAV at D5), PRCV-var-IAV, and IAV positive and negative controls. Significantly higher mean PRCV antibody titers and a significantly higher area under the curve (AUC) for PRCV shedding were observed in PRCV-var compared to PRCV-trad-pigs at D10. There was no impact on IAV infection. In conclusion, a 2020 PRCV variant isolate was similar in pathogenicity but more transmissible compared to a traditional 1989 isolate. These findings raise concerns about virus evolution towards more highly pathogenic and transmissible strains and the need to monitor such viruses.

Evaluation of the intranasal route for porcine reproductive and respiratory disease modified-live virus vaccination.

BACKGROUND: In pigs, modified live virus (MLV) vaccines against porcine reproductive and respiratory syndrome virus (PRRSV) are commonly used and administered by intramuscular (IM) injection. In contrast, PRRSV, as a primary respiratory pathogen, is mainly transmitted via the intranasal (IN) route. The objective of this study was to evaluate the efficacy of a commonly used commercial PRRSV MLV delivered IN compared to the IM route. METHODS: Fifty-four pigs were divided into five treatment groups. All vaccinated groups received the same MLV vaccine but administered via different routes. Group IN-JET-VAC was vaccinated with an automated high pressure prototype nasal jet device (IN-JET-VAC, n = 12), group IN-MAD-VAC was vaccinated with a mucosal atomization device (IN-MAD-VAC, n = 12), group IM-VAC was vaccinated intramuscularly (IM-VAC; n = 12) according to label instructions, while the NEG-CONTROL (n = 6) and the POS-CONTROL (n = 12) groups were both unvaccinated. At 28 days post vaccination all vaccinated groups and the POS-CONTROL pigs were challenged with a pathogenic US PRRSV isolate. Blood and nasal swabs were collected at regular intervals, and all pigs were necropsied at day 10 post challenge (dpc) when gross and microscopic lung lesions were assessed. RESULTS: Prior to challenge most vaccinated pigs had seroconverted to PRRSV. Clinical signs (fever, inappetence) were most obvious in the POS-CONTROL group from dpc 7 onwards. The vaccinated groups were not different for PRRSV viremia, seroconversion, or average daily weight gain. However, IN-JET-VAC and IN-MAD-VAC had significantly higher neutralizing antibody levels against the vaccine virus at challenge. CONCLUSIONS: Comparable vaccine responses were obtained in IN and IM vaccinated pigs, suggesting the intranasal administration route as an alternative option for PRRSV vaccination.

Future perspectives on swine viral vaccines: where are we headed?

Deliberate infection of humans with smallpox, also known as variolation, was a common practice in Asia and dates back to the fifteenth century. The world's first human vaccination was administered in 1796 by Edward Jenner, a British physician. One of the first pig vaccines, which targeted the bacterium Erysipelothrix rhusiopathiae, was introduced in 1883 in France by Louis Pasteur. Since then vaccination has become an essential part of pig production, and viral vaccines in particular are essential tools for pig producers and veterinarians to manage pig herd health. Traditionally, viral vaccines for pigs are either based on attenuated-live virus strains or inactivated viral antigens. With the advent of genomic sequencing and molecular engineering, novel vaccine strategies and tools, including subunit and nucleic acid vaccines, became available and are being increasingly used in pigs. This review aims to summarize recent trends and technologies available for the production and use of vaccines targeting pig viruses.

Porcine Astrovirus Type 5-Associated Enteritis in Pigs.

Astroviruses (AstVs) are emerging, potentially zoonotic pathogens, associated with enteric and neurological signs in various animal species. In pigs, five lineages have been identified, porcine AstVs (PoAstVs) 1-5. We now report PoAstV5-associated atrophic enteritis in a colostrum-deprived (CD) pig and a similar disease in field cases of enteritis. Four newborn CD piglets were housed under biosafety level 2 conditions and monitored for the presence of PoAstV RNA in rectal swabs and tissues. PoAstV4 RNA was detected in low numbers (0.9-5.3 log10 genomic copies/rectal swab) in rectal swabs from all of these pigs while all animals were negative for PoAstV1, PoAstV2, PoAstV3 and PoAstV5. At 19 and 20 days of age, high levels of PoAstV5 RNA (7.4-7.5 log10 genomic copies/rectal swab) were detected in one pig, which had developed enteritis. At necropsy 1 day after the first evidence of PoAstV5 shedding, this pig was strongly positive for PoAstV5 RNA in most tissues with strong immunolabelling of PoAstV5 in enterocytes. Gene sequencing confirmed PoAstV5 infection. A retrospective investigation of PoAstVs 3, 4 and 5 in archival tissues from field cases of post-weaning enteritis identified high PoAstV4 or PoAstV5 antigen levels in intestinal tissues. These pigs were often concurrently infected with porcine rotavirus. Our findings suggest that PoAstV5 may contribute to the pathogenesis of enteritis in young pigs.

Dissecting the potential role of hepatitis E virus ORF1 nonstructural gene in cross-species infection by using intergenotypic chimeric viruses.

Hepatitis E virus (HEV) infects humans and more than a dozen other animal species. We previously showed that open reading frame 2 (ORF2) and ORF3 are apparently not involved in HEV cross-species infection, which infers that the ORF1 may contribute to host tropism. In this study, we utilize the genomic backbone of HEV-1 which only infects humans to construct a panel of intergenotypic chimeras in which the entire ORF1 gene or its functional domains were swapped with the corresponding regions from HEV-3 that infects both humans and pigs. We demonstrated that the chimeric HEVs were replication competent in human liver cells. Subsequently, we intrahepatically inoculated the RNA transcripts of chimeras into pigs to determine if the swapped ORF1 regions confer the chimeras' ability to infect pigs. We showed that there was no evidence of infectivity in pigs for any of the chimeras. We also investigated the role of human ribosome protein sequence S17, which expanded host range in cultured cells, in HEV cross-species infection. We demonstrated that S17 insertion in HEV ORF1 did not abolish HEV replication competency in vitro, but also did not expand HEV host tropism in vivo. The results highlight the complexity of the underlying mechanism of HEV cross-species infection.

Porcine circovirus type 2a or 2b based experimental vaccines provide protection against PCV2d/porcine parvovirus 2 co-challenge.

With the discovery of Porcine circovirus type 2d (PCV2d) in the USA in 2012 and subsequent genotype shift from the previously predominant PCV2b to PCV2d in the face of widespread PCV2a vaccination, concerns over PCV2 vaccine efficacy were raised. The objective of this study was to evaluate the efficacy of two similarly produced PCV2 vaccines, one containing the PCV2a capsid and the other one containing the PCV2b capsid, in the conventional pig model against PCV2d/porcine parvovirus 2 (PPV2) co-challenge. A co-challenge was added since there is evidence that PPV2 may exacerbate PCV2 infection and since PCV2 only rarely causes disease in experimentally infected pigs, hence vaccine efficacy can be difficult to assess. In brief, sixty 3-week-old-pigs from a PCV2 seropositive farm without evidence of active virus replication (no PCV2 viremia, low antibody titers with no evidence of increase after two consecutive bleedings) were blocked by PCV2 antibody titer and then randomly divided into three groups with 20 pigs each, a non-vaccinated group (challenge control), a PCV2a vaccinated group (VAC2a) and a PCV2b vaccinated group (VAC2b). Vaccinations were done at 4 and again at 6 weeks of age. At 8 weeks of age, all pigs were challenged with a PCV2d strain via intranasal and intramuscular routes of inoculation followed by intramuscular administration of PPV2 one day later. PCV2 vaccination, regardless of PCV2 genotype, resulted in significantly higher humoral and cellular immunity compared to non-vaccinated challenge control pigs as evidenced by increased numbers of interferon (IFN) γ secreting cells after PCV2d stimulation of peripheral blood mononuclear cells collected prior to challenge. Furthermore, PCV2a and PCV2b vaccinations both reduced PCV2d viremia and PCV2-associated pathological lesions. Under the study conditions, the PCV2a and PCV2b vaccine preparations each induced immune responses and clinical protection against a heterologous PCV2d/PPV2 co-challenge.

Bacillus pumilus probiotic feed supplementation mitigates Lawsonia intracellularis shedding and lesions.

The causative agent of ileitis, Lawsonia intracellularis, is commonly associated with diarrhea and reduced weight gain in growing pigs. The effect of in-feed probiotics on L. intracellularis infection dynamics was evaluated. In brief, 70 2.5-week-old-pigs were randomly divided into six groups with 10-20 pigs each. All pigs were fed an age appropriate base ration for the duration of the study, which was supplemented with one of three Bacillus strains including B. amyloliquefaciens (T01), B. licheniformis (T02) and B. pumilus (T03). Another group was orally vaccinated with a commercial live L. intracellularis vaccine (VAC) at 3 weeks of age. At 7 weeks of age, T01-LAW, T02-LAW, T03-LAW, VAC-LAW and the POS-CONTROL groups were challenged with L. intracellularis while the NEG-CONTROL pigs were not challenged. All pigs were necropsied 16 days later. By the time of inoculation, all VAC-LAW pigs had seroconverted and at necropsy 10-65% of the pigs in all other challenged groups were also seropositive. The results indicate a successful L. intracellularis challenge with highest bacterial DNA levels in POS-CONTROL pigs, VAC-LAW pigs and T01-LAW pigs. There was a delay in onset of shedding in T02-LAW and T03-LAW groups, which was reflected in less severe macroscopic and microscopic lesions, reduced intralesional L. intracellularis antigen levels and a lower area under the curve for bacterial shedding. Under the study conditions, two of the probiotics tested suppressed L. intracellularis infection. The obtained findings show the potential of probiotics in achieving antibiotic-free control of L. intracellularis.

At the Intersection of Industry, Academia, and Government: How Do We Facilitate Productive Precision Livestock Farming in Practice?

This commentary is a comprehensive synthesis of ideas generated from a workshop, hosted by Iowa State University, encompassing precision livestock farming (PLF) research and applications for industry-academia. The goal of this workshop was to demonstrate existing institution research and strategically propel further PLF development and industry adoption. Six key thematic areas were identified from participant discussion: sensors and algorithms, implementation, economic feasibility, data, rural and societal impacts, and education and training. These themes were used to focus discussion on identifying the new knowledge needed to drive implementation and examine current and future challenges of implementing PLF. At the convergence of industry and academia sits a unique opportunity to create mutually beneficial relationships that accomplish the individual needs of all parties. Productive PLF is currently hindered by numerous technical and non-technical challenges, but an increasing demand and optimistic outlook may result in rapid producer adoption. To foster harmonious partnerships among industry, academia, and government, a nexus at the intersection of multiple disciplines and basic/applied sciences is needed to thrust future success.

A Porcine circovirus type 2b (PCV2b)-based experimental vaccine is effective in the PCV2b-Mycoplasma hyopneumoniae coinfection pig model.

Porcine circovirus type 2 (PCV2) is one of the major swine pathogens causing high economic losses due to PCV2-associated disease (PCVAD). PCV2 infection is not only immunosuppressive by damaging lymphoid tissues but is also exacerbated by co-infections with other pathogens including Mycoplasma hyopneumoniae. While PCV2 can be divided into several genotypes, currently only PCV2a, PCV2b and PCV2d are globally prevalent and considered of major importance. Most commercial PCV2 vaccines are based on PCV2a isolates; however, the high prevalence of PCV2b and PCV2d in the global pig population is raising concerns among pig veterinarians. The objective of this study was to evaluate the efficacy of an experimental PCV2b-based subunit vaccine in a combined PCV2b and M. hyopneumoniae coinfection model. Briefly, a total of 49 PCV2- and M. hyopneumoniae-free 3-week-old pigs were randomly divided into four groups: A non-vaccinated, non-infected NEG-CONTROL group, a non-vaccinated, PCV2b-infected, POS-CONTROL group, and two vaccinated and PCV2b-infected groups (SINGLE-VAC, DUAL-VAC). SINGLE-VAC and DUAL-VAC pigs were vaccinated at 3 weeks of age and DUAL-VAC pigs received a booster dose at 5 weeks of age. All pigs, except NEG-CONTROLs, were experimentally infected with M. hyopneumoniae 28 days after initial vaccination and challenged with PCV2b one week later. The pigs were necropsied 21 days after PCV2b challenge. Prior to PCV2b challenge, both vaccinated groups had detectable humoral and cell-medicated immune responses to PCV2. Vaccination significantly reduced PCV2b viremia and also reduced or eliminated PCV2-associated lymphoid lesions compared to the POS-CONTROL pigs. Under the study conditions, an experimental PCV2b vaccine protected conventional growing pigs against PCV2b viremia and associated lesions in a coinfection model with some advantages of the two-dose regimen versus the one dose regimen. Both protocols induced neutralizing antibodies against PCV2a and PCV2d prior to challenge.

A prime-boost concept using a T-cell epitope-driven DNA vaccine followed by a whole virus vaccine effectively protected pigs in the pandemic H1N1 pig challenge model.

Influenza A virus (IAV) vaccines in pigs generally provide homosubtypic protection but fail to prevent heterologous infections. In this pilot study, the efficacy of an intradermal pDNA vaccine composed of conserved SLA class I and class II T cell epitopes (EPITOPE) against a homosubtypic challenge was compared to an intramuscular commercial inactivated whole virus vaccine (INACT) and a heterologous prime boost approach using both vaccines. Thirty-nine IAV-free, 3-week-old pigs were randomly assigned to one of five groups including NEG-CONTROL (unvaccinated, sham-challenged), INACT-INACT-IAV (vaccinated with FluSure XP® at 4 and 7 weeks, pH1N1 challenged), EPITOPE-INACT-IAV (vaccinated with PigMatrix EDV at 4 and FluSure XP® at 7 weeks, pH1N1 challenged), EPITOPE-EPITOPE-IAV (vaccinated with PigMatrix EDV at 4 and 7 weeks, pH1N1 challenged), and a POS-CONTROL group (unvaccinated, pH1N1 challenged). The challenge was done at 9 weeks of age and pigs were necropsied at day post challenge (dpc) 5. At the time of challenge, all INACT-INACT-IAV pigs, and by dpc 5 all EPITOPE-INACT-IAV pigs were IAV seropositive. IFNγ secreting cells, recognizing vaccine epitope-specific peptides and pH1N1 challenge virus were highest in the EPITOPE-INACT-IAV pigs at challenge. Macroscopic lung lesion scores were reduced in all EPITOPE-INACT-IAV pigs while INACT-INACT-IAV pigs exhibited a bimodal distribution of low and high scores akin to naïve challenged animals. No IAV antigen in lung tissues was detected at necropsy in the EPITOPE-INACT-IAV group, which was similar to naïve unchallenged pigs and different from all other challenged groups. Results suggest that the heterologous prime boost approach using an epitope-driven DNA vaccine followed by an inactivated vaccine was effective against a homosubtypic challenge, and further exploration of this vaccine approach as a practical control measure against heterosubtypic IAV infections is warranted.

Refinement of a colostrum-deprived pig model for infectious disease research.

Well-defined pig models are useful to study the pathogenicity of newly recognized pathogens or strains in pigs and serve as animal models for some human diseases. The conventional pig model, where research pigs are sourced from commercial high-health production systems, is commonly used due to the easiness of getting pigs in a timely manner. However, freedom of the pig for the pathogen of interest is important at study start and serological assays to screen pigs for antibodies against newly identified pathogens or molecular assays detecting all possible circulating pathogen variants may not yet exist. Using colostrum-deprived (CD) pigs is a good alternative strategy to circumvent passively-acquired immunity against the pathogen of interest or exposure to pathogens shortly after birth. However, CD pigs are difficult to rear as they are highly susceptible to infections, and mortality rates in the first few days of life are often very high. Herein we report on refinement of a CD pig model with consistent survival rates of 90-100% of the piglets. •Step-by-step protocol to derive and rear CD piglets with higher expected survival rates.•Pig housing improvement minimizes the risk of disease transmission.•Infectious virus disease research pig model purpose.

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.

Impact of dietary spray-dried bovine plasma addition on pigs infected with porcine epidemic diarrhea virus.

Experimental data suggest that the addition of spray-dried plasma (SDP) to pig feed may enhance antibody responses against certain pathogens and negatively impact virus survival. The benefit of SDP on Escherichia coli infection is well documented. The aim of this study was to determine the effect of bovine SDP (BovSDP) in the pig diet on acute porcine epidemic diarrhea virus (PEDV) infection. A total of 16 3-wk-old conventional crossbred pigs were used and divided into three groups. Treatments included 1) a negative control group fed a commercial diet and sham inoculated with commercial liquid porcine plasma (n = 3), 2) a positive control group fed a commercial diet and inoculated with PEDV-spiked porcine plasma (PEDV; n = 8), and 3) a third group of pigs fed the commercial diet with inclusion of 5% spray-dried bovine plasma and inoculated with PEDV-spiked porcine plasma (BovSDP; n = 5). Although clinical signs associated with PEDV infection were mild in the BovSDP group, two of eight pigs in the PEDV group developed moderate clinical disease and had to be euthanized. The PEDV IgG and IgA antibody levels and prevalence rates were significantly (P < 0.05) higher in the PEDV-BovSDP group compared with the PEDV group at 7 d postinoculation. The average fecal PEDV RNA shedding time was 7.2 ± 1.0 d for the PEDV-BovSDP group and 9.3 ± 1.1 d for the PEDV group with an overall time to clearance of PEDV shedding of 11 d for PEDV-BovSDP pigs and at least 14 d for PEDV pigs, which was not different (P = 0.215). The results indicate that addition of BovSDP induced an earlier anti-PEDV antibody response in pigs experimentally infected with PEDV thereby reducing clinical disease and the amount and duration of viral shedding during acute PEDV infection.

Markedly different immune responses and virus kinetics in littermates infected with porcine circovirus type 2 or porcine parvovirus type 1.

Porcine parvovirus type 1 (PPV1) and porcine circovirus type 2 (PCV2) are small single-stranded DNA viruses with high prevalence in the global pig population. The aim of this study was to compare and contrast PCV2 and PPV1 infections in high-health status pigs and to describe PCV2 long-term infection dynamics. Six caesarian-derived colostrum-deprived pigs were randomly divided into two groups and were experimentally infected with PCV2 or PPV1 at 5 weeks of age. All pigs had detectable viremia by day (D) 3 post-infection. Pigs infected with PPV1 had a detectable INF-α response by D3 followed by a high IFN-γ response by D6. The PPV1 pigs developed antibodies against PPV1 by D6 resulting in decreasing virus titers until PPV1 DNA became undetectable from D28 until D42. In contrast, PCV2-infected pigs had no detectable INF-α or IFN-γ response after PCV2 infection. PCV2-infected pigs had no detectable anti-PCV2 humoral response until D49 and had a sustained high level of PCV2 DNA for the duration of the study. While PPV1-infected pigs were clinically normal, PCV2-infected pigs developed severe clinical illness including fatal systemic porcine circovirus associated disease (PCVAD) by D28, fatal enteric PCVAD by D56 and chronic PCVAD manifested as decreased weight gain and periods of diarrhea. Microscopically, all three PCV2-infected pigs had lymphoid lesions consistent with PCVAD and associated with low (chronic disease) to high (acute disease) levels of PCV2 antigen. Under the study conditions, there was a lack of early IFN-γ and INF-α activation followed by a delayed and low humoral immune response and persisting viremia with PCV2 infection. In contrast, PPV1-infected pigs had IFN-γ and INF-α activation and an effective immune response to the PPV1 infection.

The middle half genome of interferon-inducing porcine reproductive and respiratory syndrome virus strain A2MC2 is essential for interferon induction.

Porcine reproductive and respiratory syndrome virus (PRRSV) is known to antagonize the innate immune response. An atypical PRRSV strain A2MC2 is capable of inducing synthesis of type I interferons (IFNs) in cultured cells. Here, we show that the middle half of the A2MC2 genome is needed for triggering the IFN synthesis. First, a cDNA infectious clone of this atypical strain was constructed as a DNA-launched version. Virus recovery was achieved from the infectious clone and the recovered virus, rA2MC2, was characterized. The rA2MC2 retained the feature of IFN induction in cultured cells. Infection of pigs with the rA2MC2 virus caused viremia similar to that of the wild-type virus. Chimeric infectious clones were constructed by swapping genomic fragments with a cDNA clone of a moderately virulent strain VR-2385 that antagonizes IFN induction. Analysis of the rescued chimeric viruses demonstrated that the middle two fragments, ranging from nt4545 to nt12709 of the A2MC2 genome, were needed for the IFN induction, whereas the chimeric viruses containing any one of the two A2MC2 fragments failed to do so. The results and the cDNA infectious clone of the IFN-inducing A2MC2 will facilitate further study of its biology, ultimately leading towards the development of an improved vaccine against PRRS.

A commercial porcine circovirus (PCV) type 2a-based vaccine reduces PCV2d viremia and shedding and prevents PCV2d transmission to naïve pigs under experimental conditions.

Porcine circovirus type 2 (PCV2) vaccination has been effective in protecting pigs from clinical disease and today is used extensively. Recent studies in vaccinated populations indicate a major PCV2 genotype shift from the predominant PCV2 genotype 2b towards 2d. The aims of this study were to determine the ability of the commercial inactivated PCV2a vaccine Circovac® to protect pigs against experimental challenge with a 2013 PCV2d strain and prevent transmission. Thirty-eight pigs were randomly divided into four groups with 9-10 pigs per group: NEG (sham-vaccinated, sham-challenged), VAC (PCV2a-vaccinated, sham-challenged), VAC+CHAL (PCV2a-vaccinated and PCV2d-challenged), and CHAL (sham-vaccinated, PCV2d-challenged). Vaccination was done at 3weeks of age using Circovac® according to label instructions. The CHAL and VAC+CHAL groups were challenged with PCV2d at 7weeks of age and all pigs were necropsied 21days post-challenge (dpc). The VAC-CHAL pigs seroconverted to PCV2 by 21days post vaccination (dpv). At PCV2d challenge on 28dpv, 3/9 VAC and 1/9 VAC+CHAL pigs were seropositive. NEG pigs remained seronegative for the duration of the study. Vaccination significantly reduced PCV2d viremia (VAC+CHAL) at dpc 14 and 21, PCV2d fecal shedding at dpc 14 and 21 and PCV2d nasal shedding at dpc 7, 14 and 21 compared to CHAL pigs. Vaccination significantly reduced mean PCV2 antigen load in lymph nodes in VAC+CHAL pigs compared to CHAL pigs. When pooled serum or feces collected from VAC+CHAL and CHAL pigs at dpc 21 were used to expose single-housed PCV2 naïve pigs, a pooled fecal sample from CHAL pigs contained infectious PCV2 whereas this was not the case for VAC+CHAL pigs suggesting reduction of PCV2d transmission by vaccination. Under the study conditions, the PCV2a-based vaccine was effective in reducing PCV2d viremia, tissue loads, shedding and transmission indicating that PCV2a vaccination should be effective in PCV2d-infected herds.

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.