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Fungal Disease - Coccidioidomycosis

Etiology

Coccidioides immitis is a dimorphic fungus and soil saprophyte that is endemic to desert areas in southwestern United States, Mexico, Central America, and parts of South America.

Although primary cutaneous lesions from direct inoculation rarely occur, the organisms are more typically inhaled, and a lung infection is established that may disseminate to lymph nodes, eyes, skin, bones, and other organs.

Animal predisposition

Coccidioidomycosis is rare in cats and uncommon in dogs, with highest incidences reported in young, medium- to large-breed outdoor dogs.

Clinical signs

Skin lesions in dogs include ulcerated nodules, subcutaneous abscesses, and draining tracts over sites of long bone infection. Regional lymph adenomegaly is common. In cats, subcutaneous masses, abscesses, and draining lesions occur without underlying bone involvement. Regional lymph adenomegaly may be seen.

Other signs in dogs and cats include anorexia, weight loss, fever, and depression. Depending on the organs infected, cough, dyspnea, tachypnea, lameness from painful bone swellings, and ocular disease may be seen.

Differential diagnosis

Differentials include other fungal and bacterial infections, foreign body reaction, and neoplasia.

Diagnosis

Cytology (exudate, tissue aspirate): suppurative to (pyo) granulomatous inflammation. Fungal organisms are seldom found.

Dermatohistopathology: nodular to diffuse suppurative or (pyo) granulomatous dermatitis and panniculitis, with few to several large, round, double-walled structures (spherules) that contain endospores.

Serology: detection of antibodies against C. immitis by precipitin, complement fixation, latex agglutination, or ELISA testing. Both false-positive and falsenegative results can occur (e.g., titers can be negative in early disease, and low-level titers are common among healthy animals living in endemic areas).

Fungal culture (submit to diagnostic laboratory because fungal cultures are highly infectious): C. immitis.

Radiography: pulmonary changes are common. Osteolytic lesions develop if bone is involved.

PCR analysis, where available, may simplify the diagnosis.

Treatment

Systemic antifungal therapy should be administered over the long term (minimum 1 year if disseminated) and continued at least 2 months beyond complete clinical and radiographic resolution of the lesions. Treatment should also be continued until follow-up serum C. immitis antibody titers are negative.

Effective therapies include the following:

  • » Ketoconazole (dogs) 5–10 mg/kg PO with food q 12 hours
  • » Itraconazole (Sporanox) 5–10 mg/kg PO with food q 12 hours
  • » Fluconazole 10 mg/kg PO q 12 hours
  • » Terbinafine 30–40 mg/kg PO q 24 hours may be effective.

Prognosis: is unpredictable, and relapses are common. If relapse occurs, reinstitution of treatment until lesions resolve, followed by long-term low-dose therapy, may be needed to maintain remission.


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