Abstract
BackgroundHaemophilus parasuis is the etiological agent of Glässer’s disease, and causes severe economic losses in the swine industry. Serovar classification is intended as an indicator of virulence and pathotype and is also crucial for vaccination programs and vaccine development. According to a polysaccharide biosynthesis locus analysis, H. parasuis isolates could be classified by a molecular serotyping assay except serovars 5 and 12 detected by the same primer pair. The aim of this study was to identify H. parasuis isolates from diseased pigs in Taiwan by using a molecular serotyping assay and to analyze the relationship between serovars and pathological patterns.MethodsFrom August 2013 to February 2017, a total of 133 isolates from 277 lesions on 155 diseased animals from 124 infected herds serotyped by multiplex PCR and analyzed with pathological data.ResultsThe dominant serovars of H. parasuis in Taiwan were serovars 5/12 (37.6%), 4 (27.8%) and 13 (15%) followed by molecular serotyping non-typable (MSNT) isolates (13.5%). Nevertheless, the serovar-specific amplicons were not precisely the same sizes as previously indicated in the original publication, and MSNT isolates appeared with unexpected amplicons or lacked serovar-specific amplicons. Most H. parasuis isolates were isolated from nursery pigs infected with porcine reproductive and respiratory syndrome virus. The percentage of lung lesions (30.4%) showing H. parasuis infection was significantly higher than that of serosal lesions.DiscussionCollectively, the distribution of serovars in Taiwan is similar to that found in other countries, but MSNT isolates remain due to genetic variations. Furthermore, pulmonary lesions may be optimum sites for H. parasuis isolation, the diagnosis of Glässer’s disease, and may also serve as points of origin for systemic H. parasuis infections in hosts.
Highlights
Haemophilus parasuis, a part of normal upper respiratory microbiota, is the etiological agent of Glässer’s disease which induces sudden death, polyserositis, polyarthritis, meningitis and poor production performance, resulting in severe economic losses in the swine industry (Amano et al, 1994; Moller & Kilian, 1990; Vahle, Haynes & Andrews, 1997; Zhang et al, 2014)
Due to the persistence of cross-reactivity or non-reaction to antisera, there are still approximately 15–40% conventional serotyping cross-reactive (CSCR) and conventional serotyping non-typable (CSNT) isolates reported in a variety of countries by gel immunodiffusion assay (GID) (Table S1) (Blackall, Rapp-Gabrielson & Hampson, 1996; Cai et al, 2005; Castilla et al, 2012; Del Rio, Gutierrez & Rodriguez Ferri, 2003; Kielstein & RappGabrielson, 1992; Luppi et al, 2013; Ma et al, 2016; Oliveira, Blackall & Pijoan, 2003; RappGabrielson & Gabrielson, 1992; Rubies et al, 1999; Tadjine et al, 2004)
The principal aim of this study was to molecularly serotype H. parasuis isolated from Taiwanese diseased pigs, and correlate serovars with pathological patterns
Summary
Haemophilus parasuis, a part of normal upper respiratory microbiota, is the etiological agent of Glässer’s disease which induces sudden death, polyserositis, polyarthritis, meningitis and poor production performance, resulting in severe economic losses in the swine industry (Amano et al, 1994; Moller & Kilian, 1990; Vahle, Haynes & Andrews, 1997; Zhang et al, 2014). Despite using an indirect hemagglutination assay designed to reduce the proportion of CSCR isolates, 7.5–18% of isolates are still untypable (Table S1) (Angen, Svensmark & Mittal, 2004; Cai et al, 2005; Del Rio, Gutierrez & Rodriguez Ferri, 2003; Dijkman et al, 2012; Howell et al, 2015). This phenomenon makes it more difficult to conduct an effective vaccination program against H. parasuis. Discussion: Collectively, the distribution of serovars in Taiwan is similar to that found in other countries, but MSNT isolates remain due to genetic variations
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