Surgical removal of an anal cyst caused by a protozoan parasite (Thelohanellus kitauei) from a koi (Cyprinus carpio).

ABSTRACT

CASE DESCRIPTION An 8-month-old koi (Cyprinus carpio) fish was examined at the animal hospital at Seoul National University for anal obstruction. CLINICAL FINDINGS: The affected fish was lethargic and anorexic, appeared depressed, and had a nodular obstruction at the anus. A biopsy specimen from the anal mass was submitted for histologic examination, which revealed a number of protozoa. On the basis of the morphological characteristics of the spores and the location of the plasmodia (ie, vegetative form of the parasite), a diagnosis of a cyst containing Thelohanellus kitauei was made. Thelohanellus kitauei is a protozoan parasite that affects freshwater fish by producing cyst-like tumors that may cause intestinal obstruction. Thelohanellus kitauei infection with cystic disease has been reported to affect Cyprinus spp worldwide. TREATMENT AND OUTCOME: The cyst was removed surgically. After surgery, low-concentration tricaine methanesulfonate immersion was used for sedation and antimicrobial treatment was administered. The surgical wound healed completely, and the fish was clinically normal 14 months after surgery. CLINICAL RELEVANCE The successful outcome in this fish suggested that surgical removal may be a viable option for treatment of T kitauei infection in koi fish. The results of morphological analyses provided basic information on the relationships between tissue tropism and Thelohanellus spp.