Ct value-based real time PCR serotyping of Glaesserella parasuis

Glaesserella parasuis is the causative agent of Glässer's disease in swine. Serotyping plays an essential role in prevalence investigations and in the development of vaccination strategies for the prevention of this disease. Molecular serotyping based on variation within the capsule loci of the 15 serovars is more accurate and efficient than traditional serological serotyping. To reduce the running time and facilitate ease of data interpretation, we developed a simple and rapid cycle threshold (Ct) value-based real time PCR (qPCR) method for the identification and serotyping of G. parasuis. The qPCR method distinguished between all 15 serovar reference strains of G. parasuis with efficiency values ranging between 85.5 % and 110.4 % and, R² values > 0.98. The qPCR serotyping was evaluated using 83 clinical isolates with 43 of the isolates having been previously assigned to a serovar by the gel immuno-diffusion (GID) assay and 40 non-typeable isolates. The qPCR results of 41/43 (95.3 %) isolates were concordant with the GID assay except two isolates of serovar 12 were assigned to serovar 5. In addition, the qPCR serotyping assigned a serovar to each of the 40 non-typeable isolates. Of the 83 isolates tested to assign a serovar, a concordance rate of 98.8 % (82/83) was determined between the qPCR and the previously reported multiplex PCR of Howell et al. (2015) (including those that were either serovars 5 or 12). Despite the inability to differentiate between serovars 5 and 12, the Ct value-based qPCR serotyping represents an attractive alternative to current molecular serotyping method for G. parasuis and could be used for both epidemiological monitoring and the guidance of vaccination programs.

Development of a recombinant OppA-based indirect hemagglutination test for the detection of antibodies against Haemophilus parasuis

An indirect hemagglutination (IHA) test that could detect antibodies against Haemophilus parasuis was developed. The full-length cDNA sequence of the oligopeptide permease ABC transporter membrane protein (OppA) gene was cloned, and inserted into the prokaryotic expression vector pET-30a(+) to construct recombinant plasmid pET-30a-OppA. The recombinant OppA protein was expressed partly in soluble form in Escherichia coli BL21 (DE3) and then purified by Ni(2+) column. Furthermore, the recombinant OppA protein was used as an antigen to develop an IHA assay for detecting antibodies against H. parasuis. Results showed that this IHA test could detect species-specific antibodies against H. parasuis. Compared with currently available ELISA, the IHA test had a sensitivity of 85.0% and a specificity of 95.0%. The overall agreement between these two methods was 90.0%. The developed IHA test was used to evaluate the seroprevalence of H. parasuis in Hubei Province, China. The H. parasuis seroprevalence rate ranged from 5.5% to 26.2% in 325 tested clinical serum samples that were collected from three different pig farms in Hubei Province, China. The IHA test developed in this study will greatly contribute to the epidemiological surveys and immunization surveillance of H. parasuis.

Seroprevalence and risk factors associated with Haemophilus parasuis infection in Tibetan pigs in Tibet

Haemophilus parasuis is the causative agent of Glässer's disease, an important emerging infectious disease, but little is known of H. parasuis infection in Tibetan pigs in Tibet. The objective of the present investigation was to examine H. parasuis seroprevalence in Tibetan pigs in Tibet, China. Serum samples from 423 Tibetan pigs in Nyingchi, Tibet, China from April to December in 2010 were examined independently for the presence of antibodies against H. parasuis. A total of 147 (34.75%, 95% confidence interval [CI] 30.21-39.29) Tibetan pigs were tested positive for H. parasuis antibodies by the indirect hemagglutination assay (IHA) using a kit commercially available. 80 of 231 in Nyingchi (34.63%, 95% CI 28.50-40.77) and 67 of 192 in Mainling (34.89%, 95% CI 28.15-41.64) were tested positive, but the difference was not statistically significant (P>0.05, χ(2)=0.003). The prevalence ranged from 19.72% (95% CI 10.46-28.97) to 75.00% (95% CI 32.57-100) varying in different age groups, with higher prevalence in breeding boars than in piglets, and the difference was statistically significant (P<0.05). The prevalence of H. parasuis infection in males (45.03%, 95% CI 37.57-52.49) was significantly higher than that in the female (30%, 95% CI 22.41-37.59) pigs (P<0.05, χ(2)=7.361). Gender of Tibetan pigs was the main risk factor associated with H. parasuis infection. The results of the present survey indicated a wide distribution of H. parasuis among Tibetan pigs in Tibet, China and further investigation should better assess circulation of H. parasuis in Tibetan pigs. To the best of our knowledge, the present study represents the first report of H. parasuis infection in Tibetan pigs in China.

Immunological identification and characterization of extracellular serine protease-like protein encoded in a putative espP2 gene of Haemophilus parasuis

Haemophilus parasuis is known to produce a group of virulence-associated autotransporter (AT) proteins, VtaAs; however, no other ATs have been characterized yet. On the basis of the reported sequence of a putative espP2 gene for extracellular serine protease (ESP)-like protein of H. parasuis, this putative AT gene was successfully amplified from H. parasuis serotype 5 field strain HPS0819, cloned and sequenced. The confirmed ORF sequence showed 100% identity with the reported putative espP2 gene. The recombinant ESP-like protein purified from Escherichia coli with a pET expression system was used for immunological characterization. An approximately 85 kDa antigen was detected in cultured H. parasuis by using antiserum to the purified ESP-like protein, and antibodies against the recombinant ESP-like protein were detected in a selected serum from pigs with experimental H. parasuis infection. The results indicated that H. parasuis could produce ESP-like protein in vitro and in vivo. In an immune protection study using guinea pigs, 6 out of 10 animals immunized with the recombinant ESP-like protein survived after challenge with 5 × 10(9) bacteria of strain HPS0819, whereas 7 out of 10 animals immunized with formalin-inactivated H0819 bacterin survived after challenge. The results suggest that ESP-like protein could be one of the vaccine antigen candidates for H. parasuis infection.

Detection of a putative hemolysin operon, hhdBA, of Haemophilus parasuis from pigs with Glässer disease

The aim of the current study was to investigate whether polymerase chain reaction amplification of 16S ribosomal (r)RNA and a putative hemolysin gene operon, hhdBA, can be used to monitor live pigs for the presence of Haemophilus parasuis and predict the virulence of the strains present. Nasal cavity swabs were taken from 30 live, healthy, 1- to 8-week-old pigs on a weekly cycle from a commercial Thai nursery pig herd. A total of 27 of these pigs (90%) tested positive for H. parasuis as early as week 1 of age. None of the H. parasuis–positive samples from healthy pigs was positive for the hhdBA genes. At the same pig nursery, swab samples from nasal cavity, tonsil, trachea, and lung, and exudate samples from pleural/peritoneal cavity were taken from 30 dead pigs displaying typical pathological lesions consistent with Glässer disease. Twenty-two of 140 samples (15.7%) taken from 30 diseased pigs yielded a positive result for H. parasuis. Samples from the exudate (27%) yielded the most positive results, followed by lung, tracheal swab, tonsil, and nasal swab, respectively. Out of 22 positive samples, 12 samples (54.5%) harbored hhdA and/or hhdB genes. Detection rates of hhdA were higher than hhdB. None of the H. parasuis–positive samples taken from nasal cavity of diseased pigs tested positive for hhdBA genes. More work is required to determine if the detection of hhdBA genes is useful for identifying the virulence potential of H. parasuis field isolates.