Abstract
Swine stocks are endemically infected with the major porcine pathogen Streptococcus (S.) suis. The factors governing the transition from colonizing S. suis residing in the tonsils and the exacerbation of disease have not yet been elucidated. We analyzed the sudden death of fattening pigs kept under extensive husbandry conditions in a zoo. The animals died suddenly of septic shock and showed disseminated intravascular coagulopathy. Genotypic and phenotypic characterizations of the isolated S. suis strains, a tonsillar isolate and an invasive cps type 2 strain, were conducted. Isolated S. suis from dead pigs belonged to cps type 2 strain ST28, whereas one tonsillar S. suis isolate harvested from a healthy animal belonged to ST1173. Neither S. suis growth, induction of neutrophil extracellular traps, nor survival in blood could explain the sudden deaths. Reconstituted blood assays with serum samples from pigs of different age groups from the zoo stock suggested varying protection of individuals against pathogenic cps type 2 strains especially in younger pigs. These findings highlight the benefit of further characterization of the causative strains in each case by sequence typing before autologous vaccine candidate selection.
Highlights
Streptococcus (S.) suis is one of the main bacterial pathogens that causes high losses in nursery pigs and, is an emerging zoonotic pathogen [1,2]
At a zoo in the north-western part of Germany, sudden death without obvious clinical signs occurred in several pigs
Pigs were kept under extensive husbandry conditions, ensuring a high animal welfare level with a low pig density and the freedom for pigs to carry out species-specific behavior, including explorative behavior (Figure 1)
Summary
Streptococcus (S.) suis is one of the main bacterial pathogens that causes high losses in nursery pigs and, is an emerging zoonotic pathogen [1,2]. Assessment of the virulence of strains is complex due to the high diversity within the various serotypes, and the fact that multiple serotypes can be isolated from the same animal [2,7,8,9,10]. Serotype 2 is most frequently isolated during disease outbreaks in pigs and humans [7], followed by serotypes 1, 9, and 7, which have been considered to represent more invasive isolates [11,12,13]. The multilocus sequence typing scheme (MLST) has been used to describe the S. suis population structure and the diversity of isolates [14,15].
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