Valvular endocarditis in a pig due to Erysipelothrix rhusiopathiae
By Andrés de la Concha-Bermejillo, DVM, MS, PhD and Sonia Lingsweiler, BS, MS
The carcass of a female, approximately 112-pound Landrace-Yorkshire pig, was submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for necropsy. History noted the pig died suddenly without previous clinical signs. The pig was the only one affected of a group of swine breeding stock destined for research purposes.
At necropsy, there was extensive erythema of the skin of the ears and back of the hind legs. A moderate amount of foam oozed out of the nostrils. Approximately 500 ml of clear, straw-colored fluid were found in the thoracic and abdominal cavities. The lungs were moderately firm in consistency, but floated in water. The interlobular septae of the lung were moderately expanded with red-tinged fluid. The trachea and airways contained large amounts of foam (pulmonary edema) and mucus. The mediastinal lymph nodes were severely enlarged and dark red.
The pericardium was thickened and adhered to the epicardium. The leaflets of the bicuspid valve were severely thickened with deposition of large amounts of yellow fibrinonecrotic exudate (vegetative valvular endocarditis).
Cultures of the bicuspid valve were performed and two clear, alpha-hemolytic colonies of bacteria were isolated under anaerobic conditions on 5% sheep blood agar. Staining revealed small Gram-positive rods with some chaining. The organism was catalase-negative and produced a “bottle-brush” pattern of hydrogen sulfide along a stab line in triple sugar iron agar. MALDI-TOF (mass spectrometry) confirmed the identification as Erysipelothrix rhusiopathiae.
Erysipelothrix rhusiopathiae is facultatively anaerobic. The low numbers of organism present likely accounted for the lack of growth under aerobic conditions.
- rhusiopathiae has been recognized as a cause of disease in humans and animals since the late 1880s. It is the etiological agent of swine erysipelas and also causes economically important diseases in turkeys, chickens, ducks, emus, and less often in sheep. Swine erysipelas is an infectious disease generally seen in adults and grow-finish pigs. E. rhusiopathiae is thought to be spread among swine by carriers in the herd.
Clinically, the infection in pigs can be inapparent or may result in acute illness affecting multiple animals. Acute outbreaks generally start with sudden death of one or a few pigs. In some affected pigs, there is sudden onset of fever, depression, lethargy, anorexia, lameness, abortion, and death. In chronic cases, swine erysipelas is characterized by slow growth rate, arthritis, lameness,and signs of cardiac insufficiency due to vegetative valvular endocarditis. Rhomboid skin (diamond-skin) lesions are an inconsistent characteristic associated with acute cases. Affected pigs treated with multiple antimicrobial drugs may persist as carriers and transmit the infection to other animals and humans.
Infection in humans isconsidered an occupationally acquired zoonosis occurring mainly as a result of contact with infected animals or animal products. In humans, it can be manifested as mild cutaneous infection, a diffuse cutaneous form and rarely as a grave systemic complication with septicemia and endocarditis.
Definitive diagnosis is established by culture and isolation of the organism. Culture of E. rhusiopathiae is more likely from acute cases; failure to recover the organism should not rule-out a diagnosis of erysipelas. Other bacteria that can result in valvular endocarditis in pigs include Streptococcus suis, and less often other bacteria such as Trueperella pyogenes, Staphylococcus aureus, other staphylococci, streptococci other than S. suis, Escherichia coli, Pasteurella multocida, Listeria monocytogenes, and Actinobacillus equuli.
To learn more about this case, contact Dr. Andrés de la Concha, veterinary pathologist, or Sonia Lingsweiler, bacteriology assistant section head, at the College Station laboratory.
Jensen HE, Gyllensten J, Hofman C, Leifsson PS, Agerholm JS, Boye M, Aalbæk B. Histologic and bacteriologic findings in valvular endocarditis of slaughter-age pigs. J Vet Diagn Invest 22:921–927, 2010