Infection occurs as a result of open trauma to the skin, usually with subsequent exposure to contaminated water. The organism is of low virulence, usually producing infection only in immunosuppressed patients. The infection is usually localized and curable. Rare cases of disseminated disease, usually in severely immunocompromised individuals, have been reported. These have involved the blood, peritoneum, liver or meninges.
Neutrophilic response appears critical in eradicating infection.
Most cases from the U.S. are from the Southeast, though cases from virtually all geographic regions have been reported. Rare cases have resulted in systemic infection with fatality occurring almost exclusively in severely immunocompromised patients. No racial predilection has been noted. Erythema and pain may be associated. Patients with protothecosis bursitis present with painful swelling of the elbow, mild erythema and occasionally drainage.