An acute outbreak of Streptococcus (S.) suis in an integrated high health herd with heat stress as a possible trigger

The report describes a sudden outbreak of disease in suckling piglets associated to S. suis in a high-health herd where S. suis had never previously been demonstrated.

The high health herd was established by purchase from two SPF herds in 2002-2003, and had since been self-recruting. New genes were introduced by AI. The farm was declared free from PRRS, APP, SEP, AD, SIV, B. hyodysenteriae, Salmonella spp. and S. scabei and comprised of 324 sows in 6 groups with batch-wise farrowing, all-in-all-out with washing and desinfection between batches in farrowing and nursery.

On the 3rd of July 2015 the maximal outside temperature was 32 C and temperatures in the farrowing unit reached above 30 °C. This had a negative effect on the pen hygiene and several sows refused feed for one or a few days.

During the 6th- 7th of July, an increased number of piglets aged 1-2 weeks were diagnosed with arthritis in a group with 54 litters, and a majority of the litters were affected. Clinical signs included high fever, severe lameness from one or more joints, fatigue and mild CNS syptoms. In most cases, several piglets in a litter were ill, and in some litters all piglets were affected. In total, 150 piglets were treated individually with injections of long-acting procaine benzyl penicillin. Despite this the mortality increased in affected litters. The sows dis not express any signs of clinical disease.

A farm visit was made on the 8th of July. Three acutely ill piglets were euthanized and samples were collected from affected joints. S. suis was demonstrated by cultivation in affected joints from two of the piglets. Following that diagnose, all remaining piglets were treated individually with injections of long-acting procaine benzyl penicillin at the 13th and 15th of July.

The total mortality attributed to the outbreak amounted to 110-120 pigs. Only a few piglets died after the 15th of July.

No previous signs of infections with S. suis had been noticed in the herd that had been established from other SPF herds 13 years earlier and closed ever since. Still, as no way of introduction was identified, the most probable explanation for the outbreak is that the infection was latent in the herd, and was activated by the heat stress and the subsequent impaired hygiene. S. suis has not been diagnosed in the herd after this incidence.

Disclosure of Interest: None Declared.