Overview of Streptococcal Infections in Pigs
Of the bacterial group of gram-positive cocci comprising the genera Streptococcus, Enterococcus, and Peptostreptococcus, streptococci constitute the most significant pathogens of swine. Streptococci are also associated with infectious conditions of people, cattle, sheep, goats, and horses. Relative to pigs, S suis (an α-hemolytic Streptococcus) is by far the most important agent of infectious diseases in this group, affecting mainly nursing and recently weaned pigs. Septicemia, meningitis, polyserositis, polyarthritis, and bronchopneumonia are associated with S suis infections. Streptococcus dysgalactiae equisimilis is considered the most important β-hemolytic Streptococcus involved in lesions in pigs, and it has been judged to be of etiologic significance in autopsy reports. S porcinus, another β-hemolytic Streptococcus, has been associated particularly in the USA with a contagious clinical entity in growing pigs known as streptococcal lymphadenitis, jowl abscesses, or cervical abscesses. Enterococci reside in the intestinal tract and may cause disease in multiple species. In pigs, the E faecium species group, mainly E durans and E hirae, are especially associated with enteritis and diarrhea.