Streptococcus suis continues to be one the most frequently occurring diseases in Ontario pig farms. There are over 30 different serotypes of Strep suis isolates with some isolates being more capable of causing diseases in certain body systems than others. German researchers recently examined the serotyping and disease causing factors of Strep suis isolates that were collected between 1996 to 2016. They then compared the typing with the clinical signs of disease that these isolates were causing.
The most prominent finding was the reduction in prevalence of serotype-2/serotype-1/2 among invasive isolates during this sampling period. In diseased pigs that had systemic disease infections or respiratory disease the isolates of serotype-1/serotype-14, serotype-2/serotype-1/2, serotype 3 to 5 and 7 to 9 were most frequent. Serotype-1/serotype-14 seemed to be preferentially located in joints, serotype 4 and serotype 3 in the central nervous system, respectively.
Any one individual Strep suis isolate may possess one or more of the dozens of disease causing or virulence factors. The disease associated extracellular protein factor was almost exclusively associated with invasive serotype-1/serotype-14 and serotype-2/serotype-1/2 isolates. In contrast, lung isolates of serotype-2/serotype-1/2 mainly harbored the gene for muramidase-released protein. Serotype 4 and serotype 9 isolates from clinically diseased pigs most frequently carried the muramidase-released protein gene and the suilysin gene.
Take Home Message
Traditionally Strep suis serotype-2/serotype-1/2 caused most of the severe clinical disease associated with Strep suis but today there are a number of serotypes that are clinically active and economically significant.
Although some strains may appear to be the same or very similar based on serotyping there can be wide differences in the disease causing factors that these bacteria possess. The variation in disease causing factors appears to result in variation in clinical signs.
It is no wonder that it has been so difficult to produce a Strep suis commercial vaccine with a wide spectrum of cross protection.
Submitted by George Charbonneau, DVM
Ref: Prüfer TL, Rohde J, Verspohl J, Rohde M, de Greeff A, Willenborg J, Valentin-Weigand P. Molecular typing of Streptococcus suis strains isolated from diseased and healthy pigs between 1996-2016. PLoS One. 2019 Jan 17;14(1):e0210801. doi: 10.1371/journal.pone.0210801. eCollection 2019