Streptococcus porcinus Lancefield group E has been associated in the US with an infectious clinical entity in growing pigs known as streptococcal lymphadenitis. The disease is also called "jowl abscesses" or "cervical abscesses." Although prominent in US swine production in the 1960s, its incidence has since declined. Streptococcal lymphadenitis is not recognized as an economically important disease of pigs in other countries. Although pathology is no longer frequently observed, the organism is still prevalent in swine: tonsillar sampling at slaughterhouses is frequently positive for S porcinus.
Transmission occurs by ingestion of food or water containing the organism; abscess drainage and fecal shedding result in this environmental contamination. Organisms infect the pig through the mucosa of the pharyngeal or tonsillar surfaces and are carried to the lymph nodes, primarily of the head and neck region, where abscesses are formed. Abscesses may be noted at slaughter, and enlargement of lymph nodes in the throat region may be evident. S porcinus is also occasionally found in the vaginal mucus of sows and the semen and prepuce of boars. It is generally considered to be a secondary pathogen.
Scattered miliary abscesses develop in the mandibular, parotid, or retropharyngeal lymph nodes within 7 days after infection. By 21 days, abscesses measuring 5–8 cm in diameter are common; they destroy the internal structure of affected nodes and may extend into adjacent tissues. Developing abscesses may reach the skin, rupture, and drain in 7–10 weeks. The drained lesions heal by granulation, leaving a dense, fibrous, subcutaneous tract that resolves after several weeks. Deep abscesses may remain undetected until slaughter and tend not to drain into the pharynx.
S porcinus is sensitive to penicillins, and treatment with antimicrobials will usually resolve acute infections if detected. However, antimicrobial treatment is not usually successful in treating swine with established abscesses or in eliminating carriers. Resistance to tetracycline has been reported; however, pulsing tetracyclines in the feed at the therapeutic level of 551 g/tonne is commonly used in an attempt to control this condition. Vaccination (autogenous) is possible but has not been widely used because cervical abscesses are not a widespread problem.
S porcinus Lancefield groups P, U, and V have been isolated from lungs, genital organs, and brains of pigs. However, no histopathologic lesions could be associated with their presence. S porcinus groups P and V have also been associated with abortions in pigs.