Erysipelothrix rhusiopathiae vegetative endocarditis in a horse.

This research chronicles an unusual case of vegetative endocarditis in a horse due to an infection caused by Erysipelothrix rhusiopathiae, a bacterium more commonly associated with causing Erysipelas in pigs. The research paper describes the clinical history, diagnostic procedures, and post-mortem examination of the affected horse.

Clinical History and Diagnosis

• The case involves a 9-year old gelding or a castrated male horse, primarily used as a stock-horse, who showed symptoms of gradual weight loss over 5 months, intermittent colic episodes, and depression.
• Blood tests revealed abnormal levels of certain proteins and enzymes, indicating a disordered function of the horse’s liver.
• Despite being given additional feed and palliative treatments, the horse’s condition deteriorated with the last two days marked by the development of dependent oedema (swelling due to fluid build-up) across the ventral areas of its body.

Post-mortem Examination

• Post-mortem examination revealed multiple symptoms inclining towards severe illness, including massive oedema in ventral areas, marked ascites or fluid buildup in the abdomen, and significant enlargement of the liver.
• Crucially, the examination found two large vegetative growths adhered to the heart’s bicuspid valves, a key symptom indicating vegetative endocarditis.
• Representative organ samples, heart blood, and portions of the valves were collected for further examination and culture.

Pathology and Culture

• Microscopic examination of tissue samples indicated severe organ damage, including marked congestion and oedema in the liver, fibrosis and chronic inflammation in the kidney, and in the heart, severe endocarditis with marked fibrosis.
• Erysipelothrix rhusiopathiae bacteria were found in large numbers in heart lesions and in fewer amounts in the liver. Other organ samples were free from bacterial pathogens.
• The isolated bacteria showed sensitivity towards specific antibiotics such as penicillin, erythromycin and tetracycline, but resistance towards others like trimethoprim sulphamethoxazole, neomycin and streptomycin.
• The source of the infection remains unknown, although the paddock where the horse resided also hosted a group of feral pigs, known carriers of the E. rhusiopathiae bacterium.