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Botryomycosis has been known to affect humans, horses, cattle, swine, dogs and cats. It can occur in recently castrated horses if proper hygiene isn't followed and the end of the spermatic chord becomes infected with S. aureus.
The disease was originally discovered by Otto Bollinger (1843–1909) in 1870, and its name was coined by Sebastiano Rivolta (1832–1893) in 1884. The name refers to its grape-like granules (Gr. botryo = grapes) and the mistakenly implied fungal etiology (Gr. mykes = fungus). In 1919 the bacterial origin of the infection was discovered.
Staphylococcus aureus is usually the organism that causes the infection, however it can also be caused by Pseudomonas aeruginosa or several other species of bacteria. The anatomic structure of its lesion is similar to that of actinomycosis and mycetoma, and its granules resemble the sulfur granules of actinomycosis.
There are only a handful of documented cases of botryomycosis in humans, and its pathogenesis is not completely understood. However, it is usually described in individuals with impaired immunity, or with an underlying disease such as diabetes mellitus, cystic fibrosis or HIV infection.
Concise Review of Veterinary Microbiology - Quinn and Markey 2003