Clinical Signs

Streptococcus suis (S. suis) is a bacteria that causes several different types of clinical disease. It is most commonly isolated from herds confined that are well managed and considered "clean" of many other disease problems. Interestingly, S. suis is also frequently isolated from "normal" "healthy" pigs.

S. suis causes meningitis (brain infection), arthritis (joint infection), septicemia (blood infection), endocarditis (infection inside heart, often on the valves), pericarditis (infection outside heart) and rhinitis (nose lining infection). S. suis is frequently isolated from both lung with AND WITHOUT signs of pneumonia, therefore its role in causing pneumonia is not proven.

Suckling Piglets

Arthritis and septicemia are most commonly seen. Baby pigs joints are sore, they don't want to get up, are not aggressive nursers, are often "fading" (starve-out) pigs or get laid on. Generally only one or two piglets from a litter are affected, unlike pseudorabies. Prevention may be achieved by autogenous vaccine use in the sow, but neither vaccination of the sow or treatment of the baby pigs with antibiotics will prevent infection and the carrier state.

Nursery Pigs

Meningitis is most often seen. The pigs are usually hit by 2 weeks post-placement. They are febrile, rough hair coated, slow, and uncoordinated (aggressive penicillin or ampicillin injections at this point may be effective). The pigs quickly progress to laying on their sides and paddling, convulsing. At this stage treatment is usually useless. Prevention may be achieved by decreasing stocking density, minimizing mixing, and improving ventilation and temperature control. Vaccination of piglets with autogenous vaccines may be of some benefit. Reisolate S. suis from cases of pneumonia yearly to ensure you are using the correct strain (new strains may be introduced by breeding stock).

Finishing Pigs

S. suis has been reported to cause outbreaks of meningitis and sudden death in finishing pigs which responds to mass injection of all pigs in the building with procaine penicillin. This syndrome is not common and apparently occurs in very clean herds, possibly indicating introduction of a new strain of S. suis.

"Types"

Previously the only recognized disease causing "type" of S. suis was type 2. However recent work by Canadian researchers has established 29 serotypes. S. suis type 2 is consistently pathogenic if isolated from the brain or joints, but there are now other strains or types (4, 3, and 7) that are being isolated from diseased pigs in the United States. What effect PRRS infection has had on this observation, we do not know. We can now determine that there are now different "genotypes" of S. suis. Herds are usually infected with many different serotypes of S. suis which can be isolated from different tissues of diseased and healthy pigs. It appears that there is only one pathogenic (meningitis causing type) genotype for each herd, but this has not been thoroughly investigated. There may be different pathogenic serotypes within the same herd. Work is underway trying to determine what genes cause disease, and therefore what ones must be cloned and used to produce next generation "subunit" vaccines (vaccinating against only the disease causing parts of the bacteria).

Transmission

Pigs can be infected either during birth by passing through the birth canal of an infected sow and S. suis entering the umbilical cord or by pig to pig transmission through cuts caused by fighting or dirty processing equipment. There may also be simple respiratory transmission from pig to pig in the farrowing house and nursery. After initial infection and apparent colonization of the nose or wound, S. suis can be found in the tonsil of even healthy pigs. It appears that S. suis can be carried on the tonsils or in the lining of the nose in a quiet or "latent" state until some time that the pig becomes stressed. It has been demonstrated that S. suis can SURVIVE within macrophages and be carried to and into the brain by macrophages, the first-line-of-defense cells of the immune system!

Take-Home Message

S. suis is more common in herds with poor ventilation control and excessive crowding. Circulating PRRS virus can cause S. suis problems.

Bordetella bronchiseptica has been shown to enhance S suis problems, therefore an atrophic rhinitis vaccination program of the piglets and or sows may help in controlling S. suis.

Piglets become infected by the sow very early, perhaps during birth. S. suis can "travel" and possibly even "hide" (survive) within macrophages, therefore antibiotics cannot kill all the S. suis in the piglet. Therefore even with Medicated Early Weaning programs (medicating piglets while they are on the sow and weaning them at 10 days of age) S. suis is not eliminated.

Autogenous vaccines MAY help control S. suis problems. Use only S. suis isolated from brain samples. Isolates from other tissues MAY NOT BE DISEASE CAUSING streps. You may need to reisolate yearly to "update" your vaccine seed culture as new S. suis strains may be introduced to the herd.