Streptococcus suis

Streptococcus suis is a peanut-shaped, Gram-positive bacterium, and an important pathogen of pigs. Endemic in nearly all countries with an extensive pig industry, S. suis is also a zoonotic disease, capable of transmission to humans from pigs. Humans can be infected with S. suis when they handle infected pig carcasses or meat, especially with exposed cuts and abrasions on their hands. Human infection can be severe, with meningitis, septicaemia, endocarditis, and deafness as possible outcomes of infection. Fatal cases of S. suis are uncommon, but not unknown. Penicillin is the most common antibiotic used in treatment of S. suis infection; in cases with cardiac involvement (endocarditis), gentamicin should also be given for synergistic effect. The natural habitat of S. suis in pigs is the upper respiratory tract, particularly the tonsils and nasal cavity, and the alimentary and genital tracts. An individual pig can carry more than serotype in their nasal cavity. Incidence of disease varies but is usually less than 5%. Disease is often introduced into a noninfected herd via healthy carrier animals and during outbreaks when sick animals shed more bacteria horizontal transmission by direct contact or aerosol is important. Flies can also spread bacteria between farms and wild boar in many countries are known to carry S. suis and may be an important reservoir. The first sign in pigs is usually pyrexia and there may be sudden deaths in the herd. Respiratory disease, with pneumonia, nasal discharge and respiratory difficulties, may also be present. Neurological signs result from meningitis, and signs may be severe, ranging from tremors to seizures and death. Joints may become infected and pigs may be lame or have swollen limbs. Skin disease is another presentation, and reproductive disease can also occur. Meningitis is the most common presentation in humans. The bacterium can be isolated from various body fluids, and serological testing with an ELISA can also be performed. Most S. suis strains respond to treatment with ampicillin and amoxicillin. Anti-inflammatories should also be used. Control relies on good husbandry and biosecurity protocols and appropriate disinfection. Vaccines exist but are not reliable.