Coccidioidomycosis (Valley Fever)

Valley fever is a problem that continues to plague Southwestern United States. Coccidioides immitis is a fungus that lives in the soil. The fungus produces spores that, when the soil is disturbed, become airborne and are inhaled into the lungs. The resulting conditions are flulike symptoms that can last for up to a month in humans. There is no difference between males and non-pregnant females as to incidence of infection, however pregnant women are more susceptible. Humans between the ages of 30 and 75 are the most often infected in Arizona. According to the Arizona department of health services, the incidence of Coccidioides immitis has been steadily rising since it was first reported in the laboratory in 1997 (Arizona, 2007).

Both humans and dogs are at risk for infection. When the soil is disturbed, spores are released into the air and inhaled into the lungs. Therefore, it naturally follows that those that reside in more dusty climates are more likely to become infected than those who do not . Once the spores are inhaled, the fungus causes respiratory disease and can disseminate to other organs. Symptoms begin between 7-21 days past inhalation of the spores and can include fever, lethargy, cough and chest pain.

In dogs, C. immitis is life threatening. The most common sites of dissemination in Valley Fever are skin, bones, joints and brain meninges. Cocci meningitis is the most lethal. As a result of their closer proximity to the ground and the constant sniffing in the dirt, dogs are even more susceptible to infection with C. immitis than humans. There are two main forms of C. immitis in dogs. In one form, the fungus resides in the lungs and in the second form, the infection begins in the lungs and disseminates to other organs. The form that does not disseminate causes fever, coughing, loss of appetite and loss of energy. 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.

Cats are less frequently affected than dogs. When infected, disseminated disease is less likely to occur; however, dissemination to tissues underneath the skin occurs more often in cats than dogs. Abscesses, and chronic draining lesions are frequently observed. Due to the initial lack of symptoms, cats are often not presented for veterinary attention until dissemination has already occurred.

Dogs who recover from a benign or asymptomatic infection are resistant to a reinfection due to immunity induced by first infection.

Diagnosis The disease is often severe at the time of diagnosis. Radiographs, serum biochemistry tests and complete blood counts are usually necessary to achieve a frim doagnosis. 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.

Treatment 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.3 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.

Prognosis The prognosis is highly variable, with an estimated overall recovery rate of 60%.6 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.

In regions in which the organism is present, dogs that spend more time outdoors or have more land in which to roam are at greater risk of infection with Coccidioides spp. 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. Some occupations recommend wearing masks. Use common sense and stay out of the blowing dust.

References
1. A Proposed Vaccine for Coccidioides immitis in Dogs (http://microvet.arizona.edu)
2. 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

Go Pets America recommends seeking the advice of your local veterinarian for the most appropriate vaccination program and for the diagnosis and treatment of your pet's health problems. For vaccination requirements please contact your state and local licensing authorities.