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. 2019 May 23:7:e6817.
doi: 10.7717/peerj.6817. eCollection 2019.

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

Julia Pires Espíndola  1 , Natalia Balbinott  1 , Letícia Trevisan Gressler  1 , Gustavo Machado  2 , Catia Silene Klein  3 , Raquel Rebelatto  3 , César Bernardo Gutiérrez Martín  4 , Luiz Carlos Kreutz  1 , Anthony Bernard Schryvers  5 , Rafael Frandoloso  1
Affiliations

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

Julia Pires Espíndola et al. PeerJ. .

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.

Keywords: Brazil; Disease mapping; Haemophilus parasuis; Serovars; Typification; Vaccines.

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Conflict of interest statement

Dr. Anthony B. Schryvers is a stakeholder in Engineered Antigens Inc. that holds IP related to vaccines against human and veterinary pathogens, including H. parasuis, but this had no influence on this study. None of the authors of this paper has a financial or personal relationship with private organizations that could inappropriately influence or bias the content of the paper.

Figures

Figure 1
Figure 1. Geographic distribution of the most prevalent H. parasuis serovars for each of the ten Brazilian states.
(A) serovar 4, (B) non-typeable H. parasuis, (C) serovar 1, (D) serovar 14, (E) serovar 5, (F) serovar 12, (G) serovar 15, (H) serovar 13, (I) serovar 2.
Figure 2
Figure 2. Density map of the municipalities with Glässer’s disease outbreaks in Santa Catarina (SC) States.
The red fill area represents GD outbreaks diagnosed in the different counties of SC, which are ranked as the first in pig production of Brazil.
Figure 3
Figure 3. Distribution over the years of count number of H. parasuis field isolates.
The y-axis represents the count observations and x-axis the correspondent isolation year. (A) Number and serovar of strains isolated over the 22 years period. (B) Serovars most prevalent isolated from 2013 to 2016, which represent 69.9% of field strains analyzed. (C) Serovars less prevalent isolated from 2013 to 2016. (D) Number of isolates grouped according to virulence class (serovars) or non-typeable (NT).
Figure 4
Figure 4. Molecular capsular polysaccharide locus analysis.
(A) Illustrative scheme of the localization of funAU and wzaU primers into the locus. (B) Band patterns of the partial capsule polysaccharide locus amplification for all 15 reference serovars of H. parasuis and for 70 non-typeable Brazilian strains.
See this image and copyright information in PMC

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