Feline Coccidioidomycosis

Feline coccidioidomycosis, commonly known as Valley Fever, is a fungal infection primarily affecting cats, caused by the dimorphic fungi Coccidioides immitis or Coccidioides posadasii. This disease is endemic in arid and semiarid regions of the southwestern United States, parts of Mexico, and Central and South America. Understanding the pathogenesis, clinical signs, diagnostic approaches, and treatment strategies is crucial for effective management of this potentially debilitating condition in cats.

Etiology and Transmission

The causative agents, Coccidioides immitis and Coccidioides posadasii, reside in the soil. The life cycle of these fungi involves two distinct phases: a saprophytic phase in the soil and a parasitic phase within the host. In the soil, the fungus exists as a mold-like structure, producing arthroconidia (infectious spores). These arthroconidia become airborne when the soil is disturbed by wind, construction, or animal activity.

Cats become infected primarily through inhalation of these airborne arthroconidia. Once inhaled, the arthroconidia convert into spherules within the cat’s lungs. These spherules grow and undergo internal segmentation, eventually releasing endospores. When a spherule ruptures, it releases numerous endospores, which can then disseminate locally within the lungs or spread hematogenously (through the bloodstream) to other organs, leading to disseminated coccidioidomycosis.

Clinical Signs

The clinical presentation of feline coccidioidomycosis can be highly variable, ranging from subclinical infections to severe, life-threatening disease. The severity and type of symptoms depend on the extent of the infection and the organs involved.

Common clinical signs include:

Respiratory Symptoms:

Coughing: A persistent, often dry cough is a frequent finding.

Dyspnea (Difficulty Breathing): Shortness of breath or labored breathing can occur due to lung involvement.

Increased Respiratory Rate: A faster than normal breathing rate may be observed.

Nasal Discharge: Although less common, some cats may exhibit nasal discharge.

Systemic Signs:

Fever: Elevated body temperature is a common sign of infection.

Anorexia (Loss of Appetite): Affected cats often exhibit a decreased appetite.

Weight Loss: Progressive weight loss can occur due to the systemic effects of the infection.

Lethargy: Reduced activity level and general weakness are frequently noted.

Musculoskeletal Involvement:

Lameness: If the infection spreads to the bones, lameness or limping may be present.

Swollen Joints: Joint involvement can lead to swelling and pain.

Muscle Atrophy: Muscle wasting may occur in chronic cases.

Other Possible Manifestations:

Skin Lesions: Ulcerated or nodular skin lesions may develop if the fungus disseminates to the skin.

Ocular Signs: Uveitis (inflammation of the eye) can occur in some cases.

Neurological Signs: In rare cases, the fungus can invade the central nervous system, leading to seizures, incoordination, or other neurological abnormalities.

Abdominal Enlargement: In rare cases, abdominal organ involvement may cause distension.

Differential Diagnosis

It is important to differentiate feline coccidioidomycosis from other conditions that can cause similar clinical signs. Important differential diagnoses include:

Feline Toxoplasmosis: Both diseases can present with fever, anorexia, coughing, weight loss, and diarrhea. However, toxoplasmosis is caused by the parasite Toxoplasma gondii and may also manifest as uveitis, conjunctivitis, and abortion in pregnant cats. Diagnosis of toxoplasmosis involves serological testing and identification of the organism.

Feline Viral Rhinotracheitis: This viral infection shares symptoms like anorexia, fever, and coughing with coccidioidomycosis. However, viral rhinotracheitis typically involves sneezing, nasal discharge (serous or mucopurulent), conjunctivitis with chemosis and corneal dendritic ulcers. Diagnosis is based on clinical signs and viral isolation or PCR testing.

Feline Tuberculosis: Tuberculosis and coccidioidomycosis both can result in low-grade fever, decreased appetite, coughing, and difficulty breathing. Mycobacterium infection cause feline tuberculosis. Cats typically present with rales, initially dry cough progresses to wet cough, later becomes purulent mucus. Diagnosis involves histopathology of lung lesions and identification of acid-fast bacilli.

Feline Histoplasmosis: Fever, coughing, diarrhea, anorexia, and weight loss are common to both diseases. Histoplasmosis is caused by the fungus Histoplasma capsulatum. Vomiting and skin lesions are common with histoplasmosis. Radiographs may show nodular lesions. Diagnosis is based on culture or histopathology.

Feline Paragonimiasis: Both diseases involve coughing, diarrhea, and fever. Paragonimiasis is caused by lung fluke, Paragonimus kellicotti. Paragonimiasis shows severe morning coughing, progresses to sputum that is white, iron-stained, or brown. Diagnosis involves fecal floats with identification of flukes.

Diagnosis

Diagnosis of feline coccidioidomycosis relies on a combination of clinical findings, radiographic imaging, and laboratory testing.

Signalment and History: Knowledge of the cat’s travel history or residence in an endemic area can raise suspicion.

Physical Examination: Thorough examination to identify relevant clinical signs, particularly respiratory, musculoskeletal, or cutaneous abnormalities.

Radiography (X-rays): Chest radiographs can reveal lung lesions, such as nodules, masses, or diffuse interstitial patterns. Bone radiographs may show osteolytic lesions or periosteal proliferation in cases of bone involvement.

Cytology/Histopathology: Examination of samples from affected tissues (e.g., lung aspirates, skin biopsies, bone biopsies) can reveal the characteristic spherules of Coccidioides.

Serology: Serological tests, such as enzyme immunoassays (EIAs) or complement fixation tests (CFTs), can detect antibodies against Coccidioides in the cat’s serum. A positive serological test, in conjunction with clinical signs, supports the diagnosis of coccidioidomycosis.

Culture: Culturing Coccidioides from clinical samples is possible but requires specialized laboratory facilities and precautions due to the organism’s potential to cause human infection.

Polymerase Chain Reaction (PCR): PCR assays can detect Coccidioides DNA in clinical samples, providing a rapid and sensitive diagnostic tool.

Treatment

Treatment of feline coccidioidomycosis typically involves prolonged administration of antifungal medications. The duration of treatment can range from several months to a year or longer, depending on the severity of the infection and the cat’s response to therapy.

Commonly used antifungal drugs include:

Itraconazole: This is often the drug of choice due to its efficacy and relatively low toxicity. The typical dosage is 5-10 mg/kg orally once or twice daily.

Fluconazole: Another azole antifungal that can be effective, particularly for central nervous system involvement due to its ability to penetrate the blood-brain barrier.

Amphotericin B: This is a potent antifungal drug that is typically reserved for severe or refractory cases due to its potential for nephrotoxicity. It is administered intravenously.

Voriconazole and Posaconazole: Newer triazole antifungals that may be considered in cases that are resistant to other treatments.

Important Considerations During Treatment:

Compliance: Strict adherence to the prescribed treatment regimen is crucial for successful outcomes.

Monitoring: Regular monitoring of the cat’s clinical signs, as well as periodic blood tests to assess liver and kidney function, is essential.

Side Effects: Antifungal drugs can cause side effects such as nausea, vomiting, diarrhea, and liver toxicity. Veterinarians should educate owners about potential side effects and instruct them to report any concerns promptly.

Supportive Care: Supportive care, such as providing a balanced diet, managing pain, and addressing secondary infections, can improve the cat’s overall well-being during treatment.

Maintenance Therapy

Following the initial course of treatment, some cats may require long-term maintenance therapy with antifungal medications to prevent recurrence of the infection. The decision to use maintenance therapy is based on the individual cat’s clinical response and the risk of relapse. Long-term or even lifelong treatment may be necessary to prevent relapses.

Prevention

Preventing feline coccidioidomycosis involves minimizing the cat’s exposure to airborne arthroconidia. This can be challenging, particularly in endemic areas.

Preventive Measures:

Limit Outdoor Activity: Reducing the cat’s time spent outdoors, especially during windy or dusty conditions, can decrease the risk of exposure.

Dust Control: Minimizing dust exposure in and around the home can also help.

Relocation: For cats with recurrent infections, relocating to a non-endemic area may be considered.

Vaccination: Currently, there is no commercially available vaccine for feline coccidioidomycosis.

Prognosis

The prognosis for feline coccidioidomycosis varies depending on the severity and extent of the infection, the cat’s overall health, and the response to treatment. Cats with localized pulmonary disease generally have a better prognosis than those with disseminated disease. Early diagnosis and prompt treatment with appropriate antifungal medications can improve the chances of a successful outcome. However, some cats may require lifelong maintenance therapy to prevent relapse.

Conclusion

Feline coccidioidomycosis is a significant fungal disease that requires a thorough understanding of its etiology, clinical presentation, diagnosis, and treatment. Veterinarians should be vigilant in recognizing and managing this condition, particularly in cats residing in or traveling to endemic areas. Through a combination of antifungal therapy, supportive care, and preventive measures, it is possible to improve the prognosis and quality of life for cats affected by this challenging disease.