Molecular serotyping of clinical strains of Haemophilus (Glaesserella) parasuis brings new insights regarding Glässer's disease outbreaks in Brazil.

Julia Pires Espíndola,Luiz Carlos Kreutz,Rafael Frandoloso,Natalia Balbinott,Gustavo Machado,Letícia Trevisan Gressler,César Bernardo Gutiérrez Martín,Raquel Rebelatto,Anthony Bernard Schryvers,Catia Silene Klein

doi:10.7717/peerj.6817

Julia Pires Espíndola, Luiz Carlos Kreutz + Show 8 more

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https://doi.org/10.7717/peerj.6817

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Abstract

Glässer’s disease (GD) is an important infectious disease of swine caused by Haemophilus (Glaesserella) parasuis. Vaccination with inactivated whole cell vaccines is the major approach for prevention of H. parasuis infection worldwide, but the immunity induced is predominantly against the specific polysaccharide capsule. As a consequence, the available vaccines may not induce adequate protection against the field strains, when the capsules present in the vaccine strains are different from those in strains isolated from the farms. Therefore, it is crucial to map H. parasuis serovars associated with regional outbreaks so that appropriate bacterin vaccines can be developed and distributed for prevention of infection. In this study, 459 H. parasuis field strains isolated from different Glässer’s disease outbreaks that occurred in 10 different Brazilian States were analyzed for serotype using PCR-based approaches. Surprisingly, non-typeable (NT) strains were the second most prevalent group of field strains and along with serovars 4, 5 and 1 comprised more than 70% of the isolates. A PCR-based approach designed to amplify the entire polysaccharide capsule locus revealed 9 different band patterns in the NT strains, and 75% of the NT strains belonged to three clusters, suggesting that a number of new serovars are responsible for a substantial proportion of disease. These results indicate that commercially available vaccines in Brazil do not cover the most prevalent H. parasuis serovars associated with GD.

Highlights

Haemophilus (Glaesserella) parasuis is a pleomorphic, NAD-dependent, Gram-negative bacterium of the Pasteurellaceae family (Biberstein & White, 1969)
Since a polysaccharide capsule is invariably present in Glässer’s disease (GD) disease isolates, it has formed the basis of a serovar (SV) classification scheme used for H. parasuis (Kielstein & Rapp-Gabrielson, 1992)
The inherent heterogeneity in serovar type observed in H. parasuis isolates hamper the development of effective immunity to prevent the infection caused in pigs by different SVs than those included in the vaccines marketed against this disease

Summary

Introduction

Haemophilus (Glaesserella) parasuis is a pleomorphic, NAD-dependent, Gram-negative bacterium of the Pasteurellaceae family (Biberstein & White, 1969). Since a polysaccharide capsule is invariably present in GD disease isolates, it has formed the basis of a serovar (SV) classification scheme used for H. parasuis (Kielstein & Rapp-Gabrielson, 1992). An immunodiffusion assay has been used to classify H. parasuis into 15 serovars (SVs 1 to 15) amongst which SVs 1, 5, 10, 12, 13 and were considered highly virulent; SVs 2, 4, 8 and moderately virulent; and SVs 3, 6, 7, 9 and 11 were characterized as having low virulence potential (Kielstein & Rapp-Gabrielson, 1992). There have been reports of non-typeable strains responsible for disease outbreaks suggesting that there are other types of polysaccharide capsule in H. parasuis strains or that strains lacking capsular are capable of causing disease. It is likely that this situation applies to many other countries worldwide

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