Coccidioidomycosis, also known as valley fever, is a problem that continues to plague southwestern United States (semiarid regions of California, Arizona, New Mexico, Texas, and Northern Mexico) and semiarid regions in South America. It is caused by the dimorphic, soil-borne fungus Coccidioides immitis or Coccidioides posadasii. The fungus produces spores that, when the soil is disturbed, become airborne and are inhaled into the lungs. Once the spores are inhaled, the fungus causes respiratory disease that can spread to other organs. Symptoms begin between 7-21 days after inhalation of the spores and may include fever, lethargy, and cough. Infection by Coccidioides species occurs in a wide range of hosts, including humans, a myriad of domestic and exotic mammals, and, rarely, reptiles. Infections caused by Coccidioides may be subclinical or result in severe illness and death. In dogs, C. immitis is life threatening.
There are two main forms of C. immitis infection in dogs. In one form, the fungus resides in the lungs, while in the other form, the infection begins in the lungs and disseminates to other organs. The form that does not disseminate causes fever, cough, weakness, and loss of appetite. The form that disseminates causes lameness, swollen joints, swollen lymph nodes, and painful abscesses. Osteomyelitis is the most common form of disseminated disease in the dog, while skin lesions predominate in the cat. Other common sites of dissemination include the liver, central nervous system and, less frequently, the eye and heart muscle. Spread to these sites may be accompanied by generalized ulcerated nodules or draining tracts in the skin, seizures, eye lesions, or signs of left-sided heart failure. Dogs who recover from a benign or asymptomatic infection are resistant to reinfection due to immunity induced by initial infection. In regions in which the organism is present, dogs that spend more time outdoors are at greater risk of infection with Coccidioides. species.
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The disease is often severe at the time of diagnosis. Radiographs, serum biochemistry tests and complete blood counts are usually necessary. Skin findings may be helpful clues in the diagnosis of this increasingly important disease, but organism identification by cytology, histopathology, or culture is the only way to make a definitive diagnosis. Due to the high variability in severity and extent of disease, no standard treatment protocol has been defined. Some patients may recover without any treatment, while others may die after aggressive medical treatment. Therapy may be avoided in patients that have only mild respiratory signs. In patients with more severe pulmonary or systemic disease, long-term systemic antifungal therapy is required. The azole antifungals (ketoconazole, itraconazole, and fluconazole) are the most widely prescribed drugs in veterinary medicine, with amphotericin B used less frequently. The prognosis is highly variable, with an estimated overall recovery rate of sixty percent. Patients with mild respiratory signs usually make a full recovery, while those with disseminated disease may die or require medical treatment for the rest of their lives. Some dogs and many cats, have relapses of disease when therapy is discontinued after apparent clinical resolution. There is no prevention or vaccine at this time. Avoiding activities associated with dust and airborne dirt of native desert soil is recommended, but it is not a certain means of prevention.
Recent studies show that in some dogs with chronic coccidioidomycosis may stimulate an immune response that leads to glomerular damage and proteinuria.3
- A Proposed Vaccine for Coccidioides immitis in Dogs (http://microvet.arizona.edu)
- An Overview of Coccidioidomycosis Jana Ritter, DVM; Julie L. Webb, DVM; Bruce E. LeRoy, DVM, PhD, Dipl. ACVP; Kenneth S. Latimer, DVM, PhD, Dipl. ACVP
- Clinicopathologic and Histopathologic Renal Abnormalities in Dogs with Coccidioidomycosis. L.R. Mehrkens, 1 F.C. Mohr, 3 and J.E. Sykescorresponding author 2. J Vet Intern Med. 2016 Sep-Oct; 30(5): 1667–1671.