Coccidioidomycosis (Valley fever) is a dustborne, noncontagious infection caused by a dimorphic fungus. Infections are limited to arid and semiarid regions of the southwestern USA and to similar areas of Mexico and Central and South America. While many species of animals, including humans, are susceptible, only dogs are affected significantly.
Disseminated disease is common in dogs and causes cutaneous, osseous, cardiac, ocular, nervous system, or other organ disease.
Species which are pathogenic to dogs include:
- Coccidioides immitis
- Coccidioides posadasii
Inhalation of fungal spores is the only established mode of infection, and spores may be carried on dust particles. Epidemics may occur when rainy periods are followed by drought, resulting in dust storms.
Organs commonly affected by the disseminated disease include bones, eyes, heart, pericardium, testicles, brain, spinal cord, and visceral organs such as spleen, liver and kidneys. Disseminated disease usually manifests 4 months after development of the respiratory signs.
The primary infection is pulmonary and frequently results in chronic cough. Other symptoms include lethargy, fever, bone pain associated with osteomyelitis, lymphadenopathy, dyspnea, coughing and intermittent diarrhea. Dissemination to the skin with draining ulceration may occur, but primary infection through the skin is rare.
Coccidioidomycosis should be considered in any dog that has been potentially exposed during the previous three years and is presented with chronic illness, respiratory signs, lameness, lymphadenopathy, nonhealing cutaneous lesions, or neurological, ocular, or cardiac abnormalities.
Gross lesions may be limited to the lungs, mediastinum, heart base and thoracic lymph nodes, or may be disseminated to various organs. Lesions are discrete, variable-sized nodules with a firm, gray-white cut surface, and resemble those of tuberculosis ( Tuberculosis and Other Mycobacterial Infections: Introduction). The nodules are pyogranulomas composed of epithelioid and giant cells, and the center of some foci may contain purulent exudate and fungal organisms. Some lesions may have mineralized foci.
Definitive diagnosis can be obtained by identification of Coccidioides by cytology, biopsy or culture, as well as immunohistochemistry and in-situ hybridization. ELISA and PCR assays are also available.
In dogs with cardiac masses, surgical treatment via subtotal pericardectomy and epicardial excision is successful at relieving right-sided heart failure in dogs with effusive-constrictive pericarditis secondary to C. immitis infection, but long-term treatment with antifungal agents may still be required.
Treatment typically involves long-term antifungal therapy with terbinafine, ketoconazole (5-10 mg/kg PO BID), itraconazole (5 mg/kg PO BID) and fluconazole (5 mg/kg PO BID) for 4 - 6 months. Lifelong treatment is recommended for dogs with disseminated disease.
Amphotericin B may be used if the dog does not tolerate azoles. However, due to its narrow therapeutic index, nephrotoxicity and need for IV administration, it is not commonly used. The drug may also be administered subcutaneously.
- Merck Veterinary Manual
- Dog Heirs
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- VMSG - canine coccidioidomycosis
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