S porcinus Lancefield group E has been associated in the USA with a contagious clinical entity in growing pigs known as streptococcal lymphadenitis, jowl abscesses, or cervical abscesses. Losses due to this disease in the USA were important in the 1960s, but its incidence has since declined, and the disease is not recognized as an important economic entity in other countries, where the bacterium represents only a few percent of the microorganisms isolated from abscesses in swine. Interestingly, it was recently reported that almost 20% of tonsils from a slaughterhouse were positive for S porcinus. Although pathology is not frequently seen, the pathogen is still prevalent in swine.
Transmission is possible by contact or ingestion of food or water contaminated by purulent material from abscesses or feces containing the organism. 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 seen 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 invader.
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-seated abscesses may remain undetected until slaughter and tend not to drain into the pharynx.
S porcinus is sensitive to penicillins, and antibiotic therapy will usually resolve acute infections if detected. However, antibiotic treatment is not usually successful in treating swine with established abscesses or in eliminating carriers. Resistance to tetracycline has been reported, but pulsing tetracyclines in the feed at the therapeutic level of 400 g/ton 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 histologic lesions could be associated with their presence. S porcinus groups P and V have also been associated with abortions in pigs.
Many strains of S porcinus have been recovered from the human female genitourinary tract. However, it has been reported later that these strains belong to a different species, Streptococcus pseudoporcinus.