Han Soo Joo

Isolation of swine infertility and respiratory syndrome virus (isolate ATCC VR-2332) in North America and experimental reproduction of the disease in gnotobiotic pigs

A recent epizootic of swine infertility and respiratory syndrome (SIRS) in a Minnesota swine herd was investigated. Examination of a sow, neonatal piglets, and stillborn fetuses obtained during the epizootic from the affected herd revealed interstitial pneumonitis, lymphomononuclear encephalitis, and lymphomononuclear myocarditis in the piglets and focal vasculitis in the brain of the sow. Fetuses did not have microscopic lesions. No cause for the infertility and respiratory syndrome was determined. Therefore, attempts were made to experimentally reproduce the disease. Eleven 3-day-old gnotobiotic piglets exposed intranasally to tissue homogenates of piglets from the epizootic became inappetent and febrile by 2–4 days postexposure and had interstitial pneumonitis and encephalitis similar to that seen in the field outbreak. After 2 blind passages in gnotobiotic piglets, tissue homogenates were cultured on continuous cell line CL2621, and a cytopathic virus (ATCC VR-2332), provisionally named SIRS virus, was isolated. Gnotobiotic piglets exposed intranasally to the SIRS virus developed clinical signs and microscopic lesions that were the same as those in piglets exposed to the tissue homogenates, and the virus was reisolated from their lungs. This is the first isolate of SIRS virus in the United States that fulfills Kochs postulates in producing the respiratory form of the disease in gnotobiotic piglets and the first report of isolation and propagation of the virus on a continuous cell line (CL2621). The virus is designated as American Type Culture Collection VR-2332.

A modified serum neutralization test for the detection of antibody to porcine reproductive and respiratory syndrome virus in swine sera

Various conditions were evaluated and modified to improve the sensitivity of the serum neutralization (SN) test for detecting antibody in pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV). Higher SN titers were consistently obtained by the addition of 20% fresh swine serum to the virus diluent and by the use of a permissive cell clone (MARC-145) derived from the MA-104 cell line. Test sera used to assess the SN test were obtained from 2 groups of 3-week-old pigs infected intranasally with PRRSV (MN-1b). Using the modified method, SN antibody was first detected 9–11 days postinoculation (PI), with a peak evident at 11–21 days PI. The antibody subsequently declined, and a second peak was observed between 41 and 45 days PI. The first antibody peak was not observed and the SN antibody was only detectable between 32 and 41 days PI when the test was done with 20% heated swine serum or without supplemental swine serum. The SN antibody during 2–3 weeks PI was found to be sensitive to 2-mercaptoethanol or anti-swine IgM treatment. The SN antibody titers were high when homologous PRRSV isolate was used in the test but were markedly low for heterologous PRRSV isolates. No difference in antibody titers was observed when homologous and heterologous PRRSV isolates were tested by indirect fluorescent antibody assay. These results indicate that the modified SN method is useful in detecting earlier and higher PRRSV antibody and that it can differentiate among PRRSV isolates.

H3N2 influenza virus transmission from swine to turkeys, United States

Swinelike H3N2 influenza viruses were isolated from two geographically distinct turkey farms in the United States.

Vaccination of influenza a virus decreases transmission rates in pigs

Limited information is available on the transmission and spread of influenza virus in pig populations with differing immune statuses. In this study we assessed differences in transmission patterns and quantified the spread of a triple reassortant H1N1 influenza virus in naïve and vaccinated pig populations by estimating the reproduction ratio (R) of infection (i.e. the number of secondary infections caused by an infectious individual) using a deterministic Susceptible-Infectious-Recovered (SIR) model, fitted on experimental data. One hundred and ten pigs were distributed in ten isolated rooms as follows: (i) non-vaccinated (NV), (ii) vaccinated with a heterologous vaccine (HE), and (iii) vaccinated with a homologous inactivated vaccine (HO). The study was run with multiple replicates and for each replicate, an infected non-vaccinated pig was placed with 10 contact pigs for two weeks and transmission of influenza evaluated daily by analyzing individual nasal swabs by RT-PCR. A statistically significant difference between R estimates was observed between vaccinated and non-vaccinated pigs (p < 0.05). A statistically significant reduction in transmission was observed in the vaccinated groups where R (95%CI) was 1 (0.39-2.09) and 0 for the HE and the HO groups respectively, compared to an Ro value of 10.66 (6.57-16.46) in NV pigs (p < 0.05). Transmission in the HE group was delayed and variable when compared to the NV group and transmission could not be detected in the HO group. Results from this study indicate that influenza vaccines can be used to decrease susceptibility to influenza infection and decrease influenza transmission.

The impact of maternally derived immunity on influenza A virus transmission in neonatal pig populations

The commonality of influenza A virus (IAV) exposure and vaccination on swine farms in the United States ensures that the majority of neonatal pigs will have some degree of maternal immunity to IAV. The influence of maternal immunity on IAV transmission in neonatal pig populations will impact virus prevalence and infection dynamics across pig populations. The main objective of this study was to assess the impact of maternally derived immunity on IAV transmission in an experimental setting. Neonatal pigs suckled colostrum and derived maternal (passive) immunity from sows in one of three treatment groups: (a) non-vaccinated control (CTRL) or vaccinated with (b) homologous (PASSV-HOM) or (c) heterologous (PASSV-HET) inactivated experimental IAV vaccines. Sentinel neonatal pigs derived from the groups above were challenged with IAV via direct contact with an experimentally infected pig (seeder pig) and monitored for IAV infection daily via nasal swab sampling. A susceptible-infectious-recovered (SIR) experimental model was used to obtain and estimate transmission parameters in each treatment group via a generalized linear model. All sentinel pigs in the CTRL (30/30) and PASSV-HET (30/30) groups were infected with IAV following contact with the seeder pigs and the reproduction ratio estimates (95% confidence interval) were 10.4 (6.6-15.8) and 7.1 (4.2-11.3), respectively. In contrast, 1/20 sentinel pigs in the PASSV-HOM group was infected following contact with the seeder pigs and the reproduction ratio estimate was significantly lower compared to the CTRL and PASSV-HET groups at 0.8 (0.1-3.7). Under the conditions of this study, IAV transmission was reduced in neonatal pigs with homologous maternal immunity compared to seronegative neonatal pigs and pigs with heterologous maternal immunity as defined in this study. This study provides estimates for IAV transmission in pigs with differing types of maternal immunity which may describe the influence of maternal immunity on IAV prevalence and infection dynamics in pig populations.

Sensitivity of oral fluids for detecting influenza A virus in populations of vaccinated and non‐vaccinated pigs

Please cite this paper as: Romagosa et al. (2011) Sensitivity of oral fluids for detecting influenza A virus in populations of vaccinated and non‐vaccinated pigs. Influenza and Other Respiratory Viruses.

Evaluation of the effects of nursery depopulation on the persistence of porcine reproductive and respiratory syndrome virus and the productivity of 34 farms

Nursery depopulation has been described as an effective strategy for improving the performance of weaned pigs. In order to assess whether the strategy was effective under a wide range of conditions, a study was carried out on 34 farms in the USA. Four groups with different depopulation protocols were designed on the basis of the location of the depopulated facility (on site vs off site) and the period for which the nursery remained empty (seven days vs 14 days). The changes in average daily liveweight gain, percentage mortality, feed efficiency and treatment cost per pig produced were assessed 12 months before and after nursery depopulation. The ability to eliminate porcine reproductive and respiratory syndrome (PRRs) virus was examined by indirect fluorescent antibody testing of the nursery pigs. Significant improvements (P<0.0001) were detected in both average daily gain and percentage mortality after depopulation when the differences within an individual group were analysed, but no significant differences (P>O.14) were observed between the study groups. Serological testing indicated that antibodies to PRRS virus were still present in 14 of the 34 farms after depopulation.

Evaluation of a multiplex reverse transcription-polymerase chain reaction assay for subtyping hemagglutinin genes 1 and 3 of swine influenza type A virus in clinical samples.

A multiplex reverse transcription-polymerase chain reaction (RT-PCR) assay was developed to detect and identify subtypes of hemagglutinin (H) 1 and H3 swine influenza virus (SIV). Two oligonucleotide primer sets were prepared using published sequence data for H1N1 and H3N2. The PCR products with unique size characteristics of each subtype were sequenced, and the sequences were confirmed to be subtype specific for H gene 1 or 3. These primer sets did not amplify when RT-PCR assay was performed for genomic DNA or RNA from other common swine pathogens. The RT-PCR assay was able to detect viral RNA up to 1 tissue culture infective dose of reference SIV H1N1 or H3N2. The multiplex RT-PCR was applied to 30 SIV isolates subtyped by hemagglutination inhibition (HI) test. Forty-three positive and 20 negative swine field samples for SIV by virus isolation were also tested. Of these 73 SIV-positive samples tested, H1 and H3 were identified in 38 and 28 samples by the multiplex RT-PCR, respectively. The remaining 7 samples were positive for both H1 and H3 genes. No positive reaction was found for all 20 SIV-negative field samples. Subsequently, 235 random field samples from pigs with respiratory problems were tested by the multiplex RT-PCR, and 26 and 13 samples were found to be positive for H1 and H3, respectively. Results of these multiplex RT-PCR were comparable with those of the HI test. These results suggest that multiplex RT-PCR can be a useful test for detection and subtyping of SIV in clinical samples.

Detection of porcine reproductive and respiratory syndrome virus in pigs with low positive or negative ELISA S/p ratios

DipACVM, M. Olin, BS, T. W. Molitor, MS, PhD, H. S. Joo, DVM, PhD, C. Pijoan, DVM, PhD, Swine Disease Eradication Center, Room 385C, University of Minnesota College of Veterinary Medicine, 1988 Fitch Avenue, St Paul, MN 55108, USA K. D. Rossow, DVM, PhD, Minnesota Veterinary Diagnostic Laboratory, 1333 Gortner Avenue, St Paul, MN 55108, USA D. D. Polson, DVM, MS, PhD, Boeheringer Ingelheim Vetmedica 2501, North Loop Drive 1000, Ames, IA 50010, USA Z. Xiao, DVM, M. P. Murtaugh, PhD, Department of Veterinary Pathobiology, University of Minnesota College of Veterinary Medicine, 1971 Commonwealth Avenue, St Paul, MN 55108, USA

Comparison of protective immunity and inflammatory responses of pigs following immunization with different Actinobacillus pleuropneumoniae preparations with and without adjuvants

Three experiments were performed to evaluate the inflammatory response, the antibody response and protection from experimental challenge of various Actinobacillus pleuropneumoniae serotype 5 (Ap5) vaccines in swine. In the first experiment, subcutaneous injections of either a water-in-oil (W/O) emulsion or Freunds complete adjuvant (FCA) caused lesions at the site of injection, while intraperitoneal injection of the W/O emulsion caused no lesions. In the second experiment, intraperitoneal (IP) injection of a W/O emulsion containing unwashed Ap5 cells (6-h culture) and/or supernates from a 24-h culture resulted in severe peritoneal lesions, while W/O emulsion containing PBS-washed Ap5 cells resulted in minimal peritoneal lesions. Ap5 alone or W/O alone failed to cause peritoneal lesions. The third experiment compared the antibody response and protection from challenge of pigs immunized with either 6-h PBS-washed Ap5 cells emulsified in oil - IP, 6-hour Ap5 cells adjuvanted with dimethyl diodacyl ammonium bromide - IP, Ap5 antigen alone - IP, a commercial vaccine - subcutaneously or saline - IP. All groups, except the saline-treated group, responded with high antibody titers to Ap5 2 weeks following vaccination; however, titers from the W/O plus antigen group were significantly higher than the three other groups (P less than 0.05). Following intranasal challenge with Ap5, all animals responded with increased antibody titers. All pigs were euthanized 10 days after challenge and evaluated for pneumonia and the lungs cultured for bacteria. The lungs of all pigs, excepting the W/O plus antigen group, contained pneumonic lesions and A. pleuropneumoniae was cultured from these lesions. These results, along with results from other groups, suggest that intraperitoneal immunization using oil-adjuvanted vaccine may be an effective method for protecting pigs from pneumonia due to A. pleuropneumoniae. Its efficacy may be due to stimulation of local respiratory mucosal immunity.