Streptococcus dysgalactiae equisimilis Infection
Alpha- and nonhemolytic streptococci of Lancefield group C are defined as S dysgalactiae dysgalactiae, whereas β-hemolytic streptococci belonging to groups C, G, or L are named S dysgalactiae equisimilis.
In swine, β-hemolytic S dysgalactiae equisimilis usually belong to Lancefield group C. Although members of the normal flora, they are considered the most important β-hemolytic streptococci involved in lesions in pigs, and these agents were judged to be of etiologic significance in autopsy reports. These streptococci are common in nasal and throat secretions, tonsils, and vaginal and preputial secretions. Vaginal secretions and milk from postparturient sows are the most likely sources of infection for the piglets.
Streptococci enter the bloodstream via skin wounds, the navel, and tonsils. A bacteremia or septicemia occurs, and the organisms then settle in one or more tissues, giving rise to arthritis, endocarditis, or meningitis.
Infection is usually first seen in pigs 1–3 wk old. Joint swelling and lameness are the most obvious and persistent clinical signs. Increased temperatures, lassitude, roughened hair coat, and inappetence may also be noted. Early lesions consist of periarticular edema; swollen, hyperemic synovial membranes; and turbid synovial fluid. Necrosis of articular cartilage may be seen 15–30 days after onset and may become more severe. Fibrosis and multiple focal abscessation of periarticular tissues and hypertrophy of synovial villi also occur. Endocarditis occurs but is difficult to diagnose antemortem. Lesions consist of yellow or white vegetations of different sizes, often covering the entire surface of the affected valve.
β-hemolytic streptococci are sensitive to β-lactam antibiotics. Long-acting antibacterial agents may be beneficial, and treatment should be given before inflammation is well advanced. There are no recent reports about vaccination against these streptococci. Autogenous bacterins are sometimes used, and there were reports of a reduced incidence of arthritis when sows were vaccinated before farrowing. However, no recent data have confirmed such information.
Adequate intake of colostrum may ensure that piglets receive protective antibodies. Traumatic injuries to the feet and legs should be minimized by reducing the abrasiveness of the floor surface in the farrowing area.
S dysgalactiae is not recognized as a zoonotic pathogen.