Funguses (also called fungi) are parasitic, spore-producing organisms. They obtain their nourishment by absorbing food from the hosts on which they grow. Many species of fungus exist in the environment, but only some cause infections. The primary source of most infections is soil. Fungal infections can be acquired by inhalation, ingestion, or through the skin (for example, through a cut or wound).
Some fungal infections can cause disease in otherwise healthy animals, while others require a host that is sick, weakened, or immunocompromised to establish infection. Prolonged use of antibiotic drugs or immunosuppressive agents appears to increase the likelihood of some fungal infections. The infection itself may be localized, or it may affect the entire body. In general, fungal infections affecting the skin (such as ringworm) are common in cats, while generalized fungal infections are very rare.
Aspergillosis is a fungal infection caused by several Aspergillus species. It is primarily a respiratory infection that may rarely spread throughout the body. Aspergillosis is found worldwide and in almost all domestic animals as well as in many wild animals; however, the susceptibility to fungal infections varies among species. Nasal cavity, sinus, and lung forms have been described in domestic cats. Cats that are already stressed by disease (such as viral infection) or immunosuppressed may be more likely to become infected. Signs are nonspecific and include inflammation of the sinuses, facial swelling, and pneumonia. The fungus can also invade the central nervous system and cause neurologic signs (such as seizures). Establishing an accurate diagnosis can be difficult and may require x-rays, computed tomography, and laboratory testing. Surgery and antifungal drugs are usually recommended to treat aspergillosis; however, the outlook depends on the overall condition of the cat and the extent of infection.
Candidiasis is a localized fungal disease affecting the mucous membranes and the skin. It is distributed worldwide in a variety of animals and is most commonly caused by species of the yeast-like fungus, Candida albicans. Candidiasis is rare in cats, but has been associated with oral and upper respiratory disease, lesions of the eye, infection of the space between the lungs and chest wall, intestinal disease, and bladder infection.
Factors that may predispose an animal to infection include injury to any of the mucous membranes, the use of catheters, administration of antibiotics, and immunosuppressive drugs or diseases.
Signs of infection are variable and nonspecific (for example, diarrhea, weakness, skin lesions) and may be associated more with the primary or predisposing conditions than with the Candida infection itself. An ointment or topical application may be useful in the treatment of oral or skin candidiasis. Your veterinarian may also recommend different drugs given by mouth or by injection for treatment of infected cats.
Coccidioidomycosis is a dustborne, noncontagious infection caused by the fungus Coccidioides immitis. Infections are limited to dry, desert-like regions of the southwestern United States and similar geographic areas of Mexico and Central and South America. Inhalation of fungal spores (often carried on dust particles) is the only established mode of infection. Epidemics may occur when rainy periods are followed by drought, resulting in dust storms. Infections are uncommon in cats.
Coccidioidomycosis is primarily a chronic respiratory disease. Infected cats most often have skin problems (draining skin lesions, lumps under the skin, abscesses), fever, lack of appetite, and weight loss. Less common signs in cats include difficulty breathing, lameness, neurologic signs, and eye abnormalities. The infection spreads to multiple locations in the body in approximately half of infected cats. A diagnosis is based on blood tests or identification of the fungus in tissue samples from the animal.
Treatment involves longterm antifungal medications. The prognosis is guarded, but cats with skin infections may respond to treatment. There is no known prevention other than decreasing your pet’s exposure to desert soil and dust as much as possible in areas where the fungus occurs.
Cryptococcosis is a fungal disease that may affect the respiratory tract (especially the nasal cavity), central nervous system, eyes, and skin (particularly of the face and neck) of cats. It is caused by the fungi Cryptococcus neoformans and Cryptococcus gattii, which are found worldwide in soil and bird manure, especially in pigeon droppings. Transmission is by inhalation of spores or contamination of wounds.
Cryptococcosis is most common in cats, although it also occurs in other domestic and wild animals. In cats, upper respiratory signs following infection of the nasal cavity are most common. The signs often include sneezing; bloody, clear, or pus-filled nasal discharge; polyp-like mass(es) in the nostril; and a firm swelling under the skin and over the bridge of the nose. Areas of small raised bumps and nodules may affect the skin; these may feel soft (liquid filled) or firm. These areas may ulcerate, leaving a raw surface. Neurologic signs associated with cryptococcosis of the central nervous system include depression, changes in temperament, seizures, circling, slight paralysis, and blindness. Eye abnormalities may also develop.
Cryptococcosis is diagnosed using microscopic evaluation of samples taken from affected areas or through other laboratory tests. Various antifungal drugs may be prescribed for the treatment of cryptococcosis. Most affected pets require prolonged treatment (up to several months), depending on the severity and extent of the disease. Treatment for cryptococcosis may include surgery to remove lesions in the nasal cavity or on the bridge of the nose. The outlook for cats that are also infected with feline leukemia virus or feline immunodeficiency virus is guarded, because these cats have a higher likelihood of treatment failure.
Histoplasmosis is a noncontagious infection caused by the fungus Histoplasma capsulatum, which is found worldwide. This soil fungus is widely distributed (particularly by bird and bat populations) in the midwestern and southern United States, especially in river valleys and plains. Infection occurs when spores in the air are inhaled. The lungs and the lymph nodes in the chest are the sites of primary infection. The organisms enter the bloodstream from these sites and become dispersed throughout the body; they may localize in bone marrow or the eyes.
The signs vary and are nonspecific, reflecting the various organ involvements. Occasionally, the infection only involves the lungs, and cats show signs of fever, labored breathing, and coughing. The lung infection may resolve on its own. However, it is common for the respiratory infection to extend to other tissues, a more serious form of the disease that involves a large number of organs and body systems. The organs most often affected are the lungs, intestine, lymph nodes, liver, spleen, and bone marrow. Signs of illness such as depression, fever, and poor appetite are common, as well as difficulty breathing, chronic diarrhea, intestinal blood loss, anemia, and weight loss. Infection of the bones, eyes, skin, and central nervous system may occur. Diagnosis requires identification of the fungus in body fluids or tissues. Blood tests or x-rays may also be necessary.
Treatment of widespread histoplasmosis is difficult. It requires the use of antifungal drugs and supportive treatment, such as adequate nutrition, additional fluids (hydration), and control of secondary bacterial infections. Antifungal treatment must be continued for prolonged periods of time.
Mycetomas are infections of the skin and underlying tissues that have the appearance of nodules or tumors. When such lesions are caused by funguses, they are known as eumycotic mycetomas. The fungus multiplies in the lesions and organizes into aggregates known as granules or grains. Granules may be of various colors and sizes, depending on the species of fungus involved. Mycetomas are rare in cats.
Most eumycotic mycetomas are confined to the tissue beneath the skin, but some may be extensions of fungal infections in the abdomen. In cats, mycetomas are usually characterized by skin nodules on the legs and feet or on the face. When the feet or limbs are involved, the infection may extend to the underlying bone.
A mycetoma is diagnosed by identifying the fungus within its contents. A tissue biopsy may be necessary. Skin mycetomas, while not life-threatening, are often difficult to resolve. The outlook for abdominal mycetomas is guarded because tissue involvement is usually extensive. Your veterinarian will recommend the best treatment options, which may include surgical removal (including amputation) or antifungal medication.
Blastomycosis, caused by the fungus Blastomyces dermatitidis, is generally limited to geographically restricted areas in the Mississippi, Missouri, Tennessee, and Ohio River basins and along the Great Lakes and the St. Lawrence Seaway. It also occurs in the Pacific Northwest. Beaver dams and other habitats where soil is moist, acidic, and rich in decaying vegetation may serve as the ecologic niche for the organism, which has also been found in pigeon and bat feces. Cats are one of the most commonly affected species (in addition to people and dogs), but cats develop signs of blastomycosis in multiple organs far less commonly than dogs do.
The infective form of blastomycosis is typically inhaled into the lungs. When respiratory defenses are overwhelmed or immunosuppressed, the infection spreads from the lungs through the bloodstream. Infection can occur through the skin, but spread from a lung infection is much more common.
Affected animals have signs such as fever, lethargy, poor appetite, and weight loss. Lung involvement leads to exercise intolerance, cough, and difficulty breathing. The peripheral lymph nodes may be enlarged. Bone involvement may occur and result in lameness. Central nervous system infection may lead to behavior changes, seizures, coma, or sudden death. Infection of the urogenital tract occasionally may occur and cause signs such as blood in the urine or difficulty urinating. Eye involvement can lead to pain, light sensitivity, and glaucoma. Involvement of the retina may lead to blindness. Draining nodules or large abscesses (pockets of pus) may be found in the skin. If blastomycosis occurs in the urinary or reproductive systems, bloody urine or difficulty urinating may be seen.
Your veterinarian may suspect blastomycosis based on your cat's signs of illness, especially coughing or trouble breathing. Chest x-rays are often performed. The diagnosis can be made by identifying the fungus in affected tissue or with blood or urine tests.
Treatment of blastomycosis is based on the severity of the condition and other factors that must be evaluated by a veterinarian. Treatment is aimed at relief of specific signs (such as difficulty breathing, coughing, or eye problems) and elimination of the fungus from the body. Treatment may include one or more antifungal drugs, which are given for an extended period (often 2 months or more) until active disease is not apparent. Relapses may occur.
Phaeohyphomycosis is a general term for an infection by any of a number of pigmented funguses of the family Dematiaceae. Infection may result from fungal contamination of tissue at the site of an injury. Phaeohyphomycosis is uncommon in cats. In most cases, the infection is confined to the skin and tissues beneath the skin. Slowly enlarging masses beneath the skin are found on the toes, ears, face, and the lining of the nasal passages. Rarely, it can affect the central nervous system. The nodules may ulcerate and have draining tracts. Phaeohyphomycosis can be difficult to treat. Surgical removal of the lesion can be a cure. Treatment with antifungal drugs may be considered in cases when surgery is not possible.
Rhinosporidiosis is a chronic, nonfatal infection, primarily of the lining of the nasal passages and, occasionally, of the skin. It is caused by the fungus Rhinosporidium seeberi. Uncommon in North America, it is seen most often in India, Africa, and South America.
Infection is characterized by polyp-like growths that may be soft, pink, crumbly, lobular with roughened surfaces, and large enough to obstruct or close off the nasal passages. The skin lesions may be single or multiple, attached at a base, or have a stem-like connection.
This infection is diagnosed by identifying the fungus in a biopsied tissue sample. Surgical removal of the lesions is considered to be the standard treatment, but recurrence is common.
Sporotrichosis is a sporadic, longterm disease caused by Sporothrix schenckii. The organism is found around the world in soil, vegetation, and timber. In the US, this fungus is most commonly found in coastal regions and river valleys. Infection usually results when the organism enters the body through skin wounds via contact with plants or soil or penetrating foreign objects, such as a sharp branch. Transmission of the disease from animals, especially cats, to humans can occur. Cats can shed particularly large amounts of the fungus from infected wounds and in their feces.
Sporotrichosis is more common in cats than other species. The infection may remain localized to the site of entry (involving only the skin) or it may spread to nearby lymph nodes. In cats, affected areas are most likely to occur on the head, especially the bridge of the nose or the ears. Although generalized illness is not seen initially, longterm infection may result in fever, listlessness, and depression. Rarely, infection will spread through the bloodstream from the initial site of inoculation to the bone, lungs, liver, spleen, testes, gastrointestinal tract, or central nervous system.
Sporotrichosis is typically diagnosed by identifying the fungus in a sample of affected tissue or with a culture. Longterm treatment with antifungal drugs (continued 3 to 4 weeks beyond apparent cure) is usually recommended. Because sporotrichosis can be passed from your pet to you, strict hygiene must be observed when handling animals with suspected or diagnosed sporotrichosis. The cat's caretaker appears to be more likely to become infected than other members of the household. If your cat is diagnosed with sporotrichosis, ask your veterinarian about the precautions you and every member of your family should take while your pet is ill.
Also see professional content regarding fungal infections.