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Detection and transmission of extracellular fac-tor producing Streptococcus suis serotype 2 strains in pigs

By B. Swildens


DETECTION AND TRANSMISSION OF EXTRACELLULAR FACTOR PRODUCING STREPTOCOCCUS SUIS SEROTYPE 2 STRAINS IN PIGS INTRODUCTION Streptococcus suis (S.suis) has been implicated in the etiology of many diseases among which meningitis in pigs. The virulent extracellular factor-positive strains of S.suis serotype 2 (S.suis2EF+) have frequently been isolated from diseased. Sows carrying S.suis strains in their tonsils are considered the most important source of infection for their susceptible offspring. DETECTION OF STREPTOCOCCUS SUIS To be able to perform transmission studies, a well-defined diagnostic method was needed. We estimated the sensitivity and specificity of a polymerase chain reac-tion assay (PCR) on swabs taken from live sows. The estimated sensitivity of PCR on swabs was 0.63 (). The PCR on the whole tonsil removed after euthanasia had a higher sensitivity of 0.88 (). The specificities of both tests were around 0.96. The sensitivity of swabs can be further increased by using a slightly more invasive technique like tooth-brushes. To perform test-characterization without a golden standard, Bayesian statis-tical analysis has been increasingly used. One of the assumptions when performing a Bayesian analysis is that the tests must be conditionally independent given the dis-ease status. In our model there was only an indication for moderate conditional de-pendence particularly between Tonsil-PCR and Tonsil-BE for true positives (6.8 %). Theoretically, dependency between tests can always be parameterized, but this will lead to wider credibility intervals and thus reduce the advantages of Bayesian analy-sis. PREVENTION AND CONTROL We investigated whether S.suis2EF+ can translocate from the intestinal tract to the internal organs of pigs. Weaned pigs were transported in a truck to induce stress. Half of them were inoculated with a high amount of S.suis2EF+ through a canula placed in the proximal jejunum to exclude the tonsil as infection route. After eutha-nasia, in three animals S.suis2EF+ was re-isolated from organs in contrast to control animals, indicating intestinal bacterial translocation. To prevent S.suis intestinal translocation at farms with severe streptococcus related disease problems after weaning, management must emphasize on improving the process of weaning, such as early habituation to solid food uptake and minimizing of moving and mixing of piglets. We examined the effect of a combination of a killed S.suis 2 EF+ whole-cell vaccine combined with amoxicillin on the S.suis2EF+ carrier status of sows and their offspring housed in individual farrowing rooms. Four weeks postpartum S.suis2EF+ could not be detected in the tonsils of the seven treated sows, but the tonsils of all seven untreated sows remained positive. However, only one of the litters of these untreated sows became infected. This showed that the incidence of vertical transmis-sion in farrowing pens is low. None of the litters of the treated sows became in-fected. CONCLUDING Farming systems with lower stock densities, less mixing and strictly spatial separation of age groups can reduce the risk of outbreaks of meningitis caused by S.suis. Vaccination strategies can support the prevention of disease outbreaks. Nevertheless, incidental cases of meningitis will remain because of the persistence of carriers of pathogenic S.suis strains

Publisher: Utrecht University
Year: 2009
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