Coccidiomycosis / Valley Fever
Coccidiomycosis (a.k.a. Coccidioidomycosis or “Valley Fever”) is an infection caused by the fungus Coccidioides immitis, or a closely related species Coccidiodes posadassii. This fungus is commonly found in the southwestern United States, Mexico and areas of Central and South America. It is found in sandy, dry soils. The organism reproduces during periods of high rainfall and produces spores that become airborne during dry, windy conditions. Coccidiomycosis can infect a wide variety of animals, including dogs, cats, and horses. Humans can also be infected. Immunocompromised humans and animals are at greatest risk for severe infections. It is important to seek an examination by a veterinarian if your pet develops any signs of the disease described below.
Infection occurs by inhalation of fungal spores. Once inhaled, spores from this fungus can infect the lungs and then spread to other parts of the body. It can take 1 to 3 weeks from exposure to the first development of respiratory signs; however, most animals and people that are exposed never show signs of clinical disease. Signs of disease in the eyes and other parts of the body may not occur until 4 months or more after exposure.
Fortunately, infected animals and humans are not directly contagious. This means that a human cannot contract the disease from an infected pet from typical interactions. If multiple pets or people in a household are infected, it is most likely from a common environmental exposure, not from transmission from pets to people, from pets to pets, or from people to pets. Caution should be taken, however, to practice good hygiene and avoid direct contact with bodily fluids or open skin wounds, especially for immunocompromised persons. It is extremely rare but possible for a less severe, localized infection to be transmitted from an infected animal to a person via a bite wound. Any animal bite wound to a person, especially by an animal known to be infected, should be examined by a physician.
Coccidiomycosis can cause a wide variety of clinical signs in different body systems, which may include the following:
Eyes: Redness, cloudiness, discharge, swelling, squinting, elevation of the third eyelid, protrusion or enlargement of the eye, and blindness may occur. These are very non-specific signs and may be indicative of a variety of diseases. Valley Fever can cause inflammation inside of the eye leading to retinal detachment and glaucoma (elevated pressure inside the eye that causes discomfort and vision loss). It can also affect the eyelids and cause swelling or redness. Eyelid involvement is seen more commonly in infected cats than dogs. Occasionally, eye disease will be the only clinical sign of infection with this fungus. In up to 43% of patients, ocular disease is the only sign of infection. One or both eyes may be affected with 80% of dogs with ocular coccidiomycosis only affected in one eye.
Respiratory System: Coughing, increased effort to breathe or lethargy may be noticed. Since the infection starts with inhalation of the spores, the fungus first causes disease in the lungs. In many cases, however, respiratory signs may be mild and non-specific. Also, they may resolve prior to an onset of signs elsewhere in the body.
Skin: Slow-healing draining and/or crusted lesions can develop. These tend to be more common in cats with this infection.
Other: Decreased appetite, weight loss, lethargy, depression, fever, limping, back or neck pain, enlargement of lymph nodes and behavioral/neurologic changes, such as altered gait or seizures.
Diagnosis of Coccidiomycosis
Your veterinarian will recommend diagnostic testing based on the specific clinical signs your pet is showing. Samples from blood, urine and/or enlarged lymph nodes (if present) are commonly obtained. Tests on these samples are performed both to determine if coccidiomycosis is likely the cause of signs and to evaluate major organ function before starting treatment. Both false positive and false negative test results are possible for coccidiomycosis in endemic areas – such as Arizona. Your veterinarian will consider test results along with history and clinical signs when making a diagnosis and developing a treatment plan.
Radiographs (X-rays) and/or ultrasound are also often needed to search for signs of systemic infection. If neurologic abnormalities are present, an MRI would be recommended. Occasionally, the best method of diagnosis is from testing samples obtained directly from the eye. Some of the diagnostic tests may need to be repeated during the course of treatment to monitor response to therapy.
Treatment of Coccidiomycosis
Coccidiomycosis is treated with a long course antifungal medication. The two most commonly prescribed antifungal medications for dogs and cats with coccidiomycosis are itraconazole and fluconazole. Other antifungal medications may be recommended in some cases. Your veterinarian will make a specific recommendation based on your pet’s signs and overall systemic health. Duration of treatment can vary; however, treatment is generally continued for at least 3 to 6 months past the resolution of all signs of disease and normalization of blood antibody titers. Shorter courses of treatment have been shown to have a high incidence of relapse. Itraconazole and fluconazole are generally safe drugs; however, side effects may include liver damage and gastrointestinal upset (ie: decreased appetite, vomiting, diarrhea). For this reason, your veterinarian may recommend regular blood work to monitor for any potential side effects.
If the eyes are infected, additional treatments such as anti-inflammatory eye drops and/or anti-glaucoma medications may be indicated. Oral anti-inflammatory medications may also be prescribed. Depending on the severity of clinical signs and inflammation within the eye, medical therapy may or may not be successful in keeping your pet visual and comfortable. If medical treatment is not controlling the disease in the eye, surgical therapy may be required. Your doctor will discuss the surgical treatment options available for your pet, if necessary.
General supportive care is sometimes necessary. If so, your pet’s ophthalmologist will work closely with your primary veterinarian to make sure your pet is getting complete and appropriate treatment.
Prognosis
When coccidiomycosis affects the eye, it can be very serious and has the potential to cause permanent blindness. Prognosis for recovery depends on the severity of signs at the time of diagnosis. With the appropriate treatment, approximately 60% of patients (including those that lose vision) are able to fight off the systemic fungus and have healthy and happy lives. Prognosis is better for patients with an early diagnosis and mild signs of disease. After recovery, patients have an approximately 20% chance of relapse and reinfection is possible if your pet remains in the same environment. It is, therefore, very important to monitor your pet for any of the above clinical signs and to call your veterinarian as soon as possible if you notice any of them.
Prevention
Unfortunately, there are no vaccinations available for coccidiomycosis. Becoming familiar with the clinical signs mentioned above is the best way to help your pet. It is important to contact your veterinarian if signs occur. Being proactive will provide the best chance for recovery. Avoiding outdoor activity during dry, windy conditions and discouraging digging may reduce risk of exposure.
