T-cell epitope content comparison (EpiCC) of swine H1 influenza A virus hemagglutinin

Background

Predicting vaccine efficacy against emerging pathogen strains is a significant problem in human and animal vaccine design. T‐cell epitope cross‐conservation may play an important role in cross‐strain vaccine efficacy. While influenza A virus (IAV) hemagglutination inhibition (HI) antibody titers are widely used to predict protective efficacy of 1 IAV vaccine against new strains, no similar correlate of protection has been identified for T‐cell epitopes.

Objective

We developed a computational method (EpiCC) that facilitates pairwise comparison of protein sequences based on an immunological property—T‐cell epitope content—rather than sequence identity, and evaluated its ability to classify swine IAV strain relatedness to estimate cross‐protective potential of a vaccine strain for circulating viruses.

Methods

T‐cell epitope relatedness scores were assessed for 23 IAV HA sequences representing the major H1 swine IAV phylo‐clusters circulating in North American swine and HA sequences in a commercial inactivated vaccine (FluSure XP^®). Scores were compared to experimental data from previous efficacy studies.

Results

Higher EpiCC scores were associated with greater protection by the vaccine against strains for 23 field IAV strain vaccine comparisons. A threshold for EpiCC relatedness associated with full or partial protection in the absence of cross‐reactive HI antibodies was identified. EpiCC scores for field strains for which FluSure protective efficacy is not yet available were also calculated.

Conclusion

EpiCC thresholds can be evaluated for predictive accuracy of protection in future efficacy studies. EpiCC may also complement HI cross‐reactivity and phylogeny for selection of influenza strains in vaccine development.

Two clinical isolates of Mycoplasma hyosynoviae showed differing pattern of lameness and pathogen detection in experimentally challenged pigs

Mycoplasma (M.) hyosynoviae is known to colonize and cause disease in growing-finishing pigs. In this study, two clinical isolates of M. hyosynoviae were compared by inoculating cesarean-derived colostrum-deprived and specific-pathogen-free growing pigs. After intranasal or intravenous inoculation, the proportion and distribution pattern of clinical cases was compared in addition to the severity of lameness. Tonsils were found to be the primary site of colonization, while bacteremia was rarely detected prior to the observation of clinical signs. Regardless of the clinical isolate, route of inoculation, or volume of inocula, histopathological alterations and tissue invasion were detected in multiple joints, indicating an apparent lack of specific joint tropism. Acute disease was primarily observed 7 to 10 days post-inoculation. The variability in the severity of synovial microscopic lesions and pathogen detection in joint cavities suggests that the duration of joint infection may influence the diagnostic accuracy. In summary, these findings demonstrate that diagnosis of M. hyosynoviae-associated arthritis can be influenced by the clinical isolate, and provides a study platform to investigate the colonization and virulence potential of field isolates. This approach can be particularly relevant to auxiliate in surveillance and testing of therapeutic and/or vaccine candidates.

In vivo evaluation of vaccine efficacy against challenge with a contemporary field isolate from the α cluster of H1N1 swine influenza virus

Influenza A virus vaccines currently contain a mixture of isolates that reflect the genetic and antigenic characteristics of the currently circulating strains. This study was conducted to evaluate the efficacy of a trivalent inactivated swine influenza virus vaccine (Flusure XP) in pigs challenged with a contemporary α-cluster H1N1 field isolate of Canadian swine origin. Pigs were allocated to vaccinated, placebo, and negative-control groups and monitored for respiratory disease for 5 d after challenge. On the challenge day and 5 d after challenge the serum of the vaccinated pigs had reciprocal hemagglutination inhibition antibody titers 40 for all the vaccine viruses but ≤ 20 for the challenge virus. Gross lesions were present in the lungs of all pigs that had been inoculated with the challenge virus, but the proportion of lung tissue consolidated did not differ significantly between the placebo and vaccinated pigs. However, the amount of virus was significantly reduced in the nasal secretions, lungs, and bronchoalveolar lavage fluid in the vaccinated pigs compared with the placebo pigs. These results indicate that swine vaccinated with Flusure XP were partially protected against experimental challenge with a swine α-cluster H1N1 virus that is genetically similar to viruses currently circulating in Canadian swine.

A novel signature-tagged mutagenesis system for Streptococcus suis serotype 2

Streptococcus suis is an economically important, zoonotic pathogen causing death and disease in swine. The objectives of this study were to develop a signature-tagged mutagenesis (STM) system for S. suis serotype 2 and to identify genes required for in vivo virulence. Identification of such candidate genes may lead to a better understanding of the pathogenesis of S. suis and may provide substrate for the discovery of new vaccines. A novel STM approach was designed to allow for a higher throughput assay of mutants using the Luminex xMAP system. Additionally, to speed the identification process, a direct genomic DNA sequencing method was developed that overcomes the problems associated with the presence of repetitive insertion sequences. Approximately 2600 mutants were screened through both mouse and caesarian-derived, colostrum-deprived (CDCD) pig models. The disrupted ORF was identified for each potential attenuated mutant, and mutants with distinct and unique mutated ORFs were analyzed individually for attenuation in mouse and CDCD pig models. A variety of genes were identified, including previously known genes essential to the virulence of other organisms, genes involved in capsule biosynthesis, a regulator of suilysin expression, and several conserved or predicted genes. Of the 22 mutants identified as attenuated in either animal model, eight insertion mutants caused no mortality in both mouse and pig models.

Serological characterisation of Haemophilus parasuis isolates from Australian pigs

A total of 31 isolates of Haemophilus parasuis obtained from Australian pigs were serotyped by the Kielstein-Rapp-Gabrielson scheme. The isolates were assigned to serovar 1 (1 isolate), serovar 2 (1 isolate), serovar 4 (4 isolates), serovar 5 (7 isolates), serovar 9 (2 isolates), serovar 10/7 (4 isolates), serovar 12 (1 isolate) and serovar 13 (6 isolates). The remaining 5 isolates could not be assigned to a serovar. Two different serovars (5 and 13) were detected in one herd. The only 2 isolates obtained from clinically normal pigs (from the same herd) were serovar 9. The common serovars were isolated from pigs with pneumonia as well as from pigs with conditions of the Glässer's disease type. The serological heterogeneity amongst Australian isolates of H parasuis has important implications for the use of vaccines to control Glässer's disease.

Comparative virulence of Haemophilus parasuis serovars 1 to 7 in guinea pigs

Reference strains for Haemophilus parasuis serovars 1 to 7 were examined for virulence by inoculation of guinea pigs. Guinea pig response to intraperitoneal inoculation was similar for the 7 reference strains. However, apparent differences in virulence were detected after intratracheal inoculation. Cells of the references strains for serovars 1 and 5 were most invasive, causing moribundity or death at higher doses and a persistent septicemia at lower doses. Haemophilus parasuis could be isolated from respiratory and systemic sites; purulent bronchopneumonia, pericarditis, and pleuritis were apparent in infected guinea pigs. Inoculation of cells of the reference strains for serovars 2 and 6 also resulted in bronchopneumonia and moribundity or death in some guinea pigs; however, reisolation of H parasuis and microscopic lesions at necropsy were less pronounced than those observed with serovars 1 and 5. Inoculation of cells of serovars 3, 4 and 7 induced only transient clinical signs and minimal evidence of H parasuis infection at necropsy. The data from intratracheal inoculation of guinea pigs are similar to data from other investigations in swine, indicating differences in the pathogenic potential of H parasuis strains. Thus, guinea pigs may be useful as a laboratory animal model for examining cellular factors associated with virulence and immunogenicity of H parasuis.

Prevalence of Haemophilus parasuis serovars among isolates from swine

Two hundred sixty Haemophilus spp isolates that had been obtained from the respiratory tract and other sites of swine were acquired from diagnostic laboratories, primarily in the United States and Canada. The majority of isolates (243/260) were biochemically characterized as H parasuis; however, a few isolates of taxa distinct from H parasuis (taxa "minor group," D, E, and F) were identified. Fourteen H parasuis serovars were identified, and of those previously described, the most prevalent were 5 (24.3% of isolates), 4 (16.1%), 2 (8.2%), and 7 (3.7%). Three new serovars that were also prevalent included ND4 (11.1%), ND3 (8.6%), and ND5 (6.6%). Serovars 1, 3, 6, C, D, and new serovars ND1 and ND2 were infrequently identified, and 15.2% of isolates were nontypeable. It was not uncommon to isolate multiple serovars from swine of the same herd or related herds. Distribution of serovars among isolates from the United States and Canada was generally similar; however, a higher prevalence of serovar 5 and a lower prevalence of serovars 2, ND3, and ND5 were evident in isolates from Canada. Comparison of isolates obtained from the respiratory tract of swine without polyserositis with those obtained from swine with polyserositis revealed an increased frequency of serovars 4 and 5, and a decreased frequency of serovar 2, among isolates from swine with polyserositis. However, all prevalent serovars were isolated from swine with polyserositis, and data were not indicative of an association between serovar, site of isolation, or pathogenic potential.

Designation of 15 serovars of Haemophilus parasuis on the basis of immunodiffusion using heat-stable antigen extracts

Previous independent investigations of the serotyping of Haemophilus parasuis strains have led to the designation of serovars A to D, 1 to 7, Jena 6 to Jena 12, and ND1 to ND5. Heat-stable antigen preparations from the reference strains for these serovars were tested by immunodiffusion with rabbit hyperimmune antisera. The existence of 15 distinct serologic groups was apparent, for which we propose the designations serovars 1 to 15. Examination of 290 field isolates from swine in the former German Democratic Republic indicated a prevalence of serovars 4 and 5, which together accounted for 41% of the isolates examined. However, 26.2% of the isolates were nontypeable with this test procedure and available antisera. Intraperitoneal inoculation of specific-pathogen-free pigs with cells representing the 15 serovars indicated differences in virulence which may be serovar related. Cells of strains representing serovars 1, 5, 10, 12, 13, and 14 were the most virulent, causing death or moribundity in inoculated pigs. Cells of serovars 2, 4, 8, and 15 caused polyserositis, but not death, in inoculated pigs. However, inoculation of cells of strains representing serovars 3, 6, 7, 9, and 11 resulted in no clinical symptoms or lesions indicative of H. parasuis infection.

Improved protection of swine from pleuropneumonia by vaccination with proteinase K-treated outer membrane of Actinobacillus (Haemophilus) pleuropneumoniae

The immunogenic and protective potentials of an outer membrane-enriched fraction (OM) from a serotype 5 strain of Actinobacillus (Haemophilus) pleuropneumoniae (APP) and the same OM degraded with proteinase K or periodate were evaluated in swine. Groups of pigs were vaccinated with two doses of OM, proteinase K-treated OM (P-OM), periodate-treated OM (PI-OM), or placebo vaccine and challenged intranasally with the homologous strain of APP. Results from triplicate experiments indicated that proteinase K treatment of OM resulted in an improved efficacy. This improved efficacy of P-OM vaccine over untreated OM vaccine was evidenced not only by less severe lung lesions in P-OM vaccinated pigs but also by significant reduction (P less than 0.05) in the number of P-OM vaccinated pigs which developed lung lesions upon challenge with APP. Assessment of sera from vaccinated animals by immunoblotting, complement fixation test, or ELISA indicated that the immunogenicity of some but not all protein or carbohydrate components were reduced (or eliminated) by proteinase K and periodate treatments respectively.