Canine and Feline Cryptococcosis

Cryptococcosis is caused by a Gram-positive yeast that has worldwide distribution with an increased incidence in temperate regions such as southern California and Australia. It affects numerous species, including dogs, cats, and humans. Cryptococcus neoformans is the species that primarily causes this disease in domestic pets.

Several sources of this yeast exist, including bird (especially pigeon) excreta which contain high amounts of nitrogen-containing compounds such as creatinine, soil and fruits. Cryptococcus species can survive in feces for up to two years. It does not spread via direct contact but instead is transmitted by inhalation of the organism from the soil or feces. Cryptococcus neoformans var. gattii is primarily found in tropic and subtropic areas due to its very specific habitat of Eucalyptus trees.

Signs The four groups of organs affected are the respiratory tract, central nervous system, eyes, and skin. The clinical signs, therefore, depend on the system(s) affected. Respiratory infections (seen in > 80% of cases) are characterized by sneezing, nasal discharge (pus-filled, bloody, or clear), swelling underneath the skin in the nasal area, mouth lesions, and swelling of lymph nodes. Neurological signs vary with the location of the lesion and can include depression, poor movement coordination, seizures, partial paralysis, and blindness. Eye abnormalities predominately affect the retina, choroid, and optic nerve. Clinical signs can range from dilated, unresponsive pupils and blindness to chorioretinitis, anterior uveitis, and retinal damage. While the prognosis for survival with the ocular form of Cryptococcus is fair to good using triazole antifungals, the prognosis for return of vision is guarded to poor due to retinal damage.

Skin lesions are seen in approximately 45% of infected animals and often occur with additional organs simultaneously being affected. The skin lesions are more likely caused by previous spreading of the infection to the skin. A more rare presentation of cryptococcosis may include bone destruction, chronic cough, and kidney failure.

Dogs are infected by C. neoformans much less frequently than cats (7-10 times more likely to be infected). The average age of infected dogs is 3.5 years and, unlike cats, there is no gender predisposition. Overrepresented dog breeds include American Cocker Spaniels and Labrador Retrievers in North America, and Doberman Pinschers and Great Danes in Australia. Cryptococcosis affects the same four organ systems as with cats, but the CNS and eyes are more commonly involved in dogs than in cats. The clinical signs are similar to those found in cats except that fever (103-105° F) is seen more often in affected dogs (25% of cases).

Diagnosis The most rapid and practical means of diagnosing Cryptococcus neoformans is by laboratory test (examination or nasal discharge and urine analysis).

Treatment Amphotericin B (AMB), alone or in combination with other antifungal drugs, has been previously used to treat cryptococcosis. However, this drug is usually reserved for life-threatening and previously unresponsive cases due to its toxicity. Several disadvantages of AMB make it less desirable than other drugs. Intravenous treatment is difficult and causes many adverse reactions, AMB has side-effects including nephrotoxicity and severe azotemia, it has poor efficacy in dogs, and is ineffective with cryptococcal meningitis because AMB does not cross the blood-brain barrier (BBB)

ketoconazole is another treatment option for cryptococcosis. itraconazole is a triazole antifungal drug similar to KTZ but with fewer adverse side-effects. Fluconazole (FCZ) is another triazole agent that does have the ability to cross the BBB and has fewer side effects than the aforementioned antifungal compounds. FCZ has been reported to have the highest success rates in cats, including those with advanced, longstanding, or disseminated disease.

Prognosis Outcomes of treatment of cryptococcosis are quite varied. Drug therapy is long-term (average of 8.5 months) and relapses occur frequently. Patients with the CNS form of cryptococcosis will require lifelong treatment maintenance. The prognosis is much worse if the patient has the neurologic form of disease or is immunocompromised by FeLV or FIV infections. Since Cryptococcus neoformans is ubiquitous, the best means of prevention is to decrease contact with areas containing a high concentration of organisms (pigeon droppings, damp buildings or basements).

Cryptococcosis in Cats

Cryptococcosis is the most common fungal disease in cats and should be an important differential diagnosis when a cat presents with sneezing and nasal discharge that is unresponsive to antibiotics. The age range of infected cats varies widely (1-13 yrs), with a mean age of 5 years. There is a predilection for infection in male cats, most likely due to the increased roaming of toms. Siamese cats are also overrepresented in most studies. Outdoor cats also have an increased predominance of cryptococcosis as compared with indoor cats. However, keeping cats indoors does not prevent them from contracting the disease. Potting soil in house plants and moldy, unfinished basements may be sources of infection in indoor cats.

References
1. Cecily A. Reynolds, DVM; Perry J. Bain, DVM, PhD; and Kenneth S. Latimer, DVM, PhD Department of Pathology (Bain, Latimer), College of Veterinary Medicine, The University of Georgia

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.