Fungal Diseases in Cats
Fungi are a large family that includes mushrooms. They live in soil and organic material. Many types of fungi spread via airborne spores. Fungus spores, which resist heat and can live for long periods without water, gain entrance to the body through the respiratory tract or a break in the skin.
Fungal diseases can be divided into two categories. The first are fungi that affect only the skin or mucous membranes, such as ringworm and thrush. In the second category, the fungus is widespread and involves the liver, lungs, brain, and other organs, in which case the disease is systemic.
Systemic diseases are caused by fungi that live in soil and organic material. Spores, which resist heat and can live for long periods without water, gain entrance through the respiratory system or through the skin at the site of a puncture. Systemic fungal diseases tend to occur in chronically ill or poorly nourished cats.
Fungal diseases are difficult to recognize and treat. X-rays, biopsies, fungal cultures, and serologic blood tests are used to make a diagnosis. Suspect a fungus when an unexplained infection fails to respond to a full course of antibiotics. Although many systemic fungal agents can both infect humans and cats, only Sporotrichosis has been shown to infect humans following direct exposure to infected cats.
This disease, caused by the yeastlike fungus Cryptococcus neoformans, is the most common systemic fungal infection of cats. It tends to occur in young adult animals. It is acquired by inhaling spores found in soil heavily contaminated by bird droppings, especially those of pigeons. The likelihood of infection is increased if the cat has an immune deficiency. However, not all cats who develop cryptococcosis are immune depressed.
Nasal cryptococcosis occurs in 50 percent of cases. Signs include sneezing, snuffling, a mucoid to bloody discharge from one or both nostrils, coughing, and obstructed breathing. Flesh-colored polyplike growths may protrude from the nose. The infection may extend to the brain and cause fatal meningitis with neurological signs such as circling and seizures. Ocular damage, including blindness, may also be noted.
Cutaneous cryptococcosis, which occurs in 25 percent of cases, frequently produces a firm swelling over the bridge of the nose. The face and neck are other common sites.
Neurologic cryptococcosis can show a variety of signs, depending on where the infection is located. These include blindness, seizures, and vestibular signs, such as incoordination or a head tilt. The diagnosis can be made by fungus culture or tissue biopsy. Often, the organisms can be identified in a smear from the nasal discharge. A cryptococcus latex agglutination test is available.
Treatment: Oral antifungal drugs of the imidazole group, such as ketoconazole, are effective when started early in the course of the disease. Fluconazole and itraconazole are newer drugs that are far better tolerated by cats. These drugs are slow acting. Treatment is prolonged. If those drugs are not successful, amphotercin B or flucytosine can be tried, but they are medications of last resort because they have many serious side effects.
This disease is caused by a fungus found in the central United States near the Great Lakes, the Appalachian Mountains, Texas, and the valleys of the Mississippi, Ohio, and St. Lawrence Rivers. In these areas, the nitrogen-rich soil facilitates growth of the causative fungus (Histoplasma capsulatum).
In the majority of cats, histoplasmosis is an insidious disease with fever, loss of appetite, weakness, weight loss, and debilitation. The liver, respiratory system, eyes, and skin may be involved. Lameness may be noted.
Treatment: Successful treatment with antifungal drugs, such as itraconazole, depends on early diagnosis. Despite treatment, most cats die from this infection. Mild respiratory cases have the best prognosis
This uncommon skin infection is caused by fungus spores in the soil. These spores usually gain access through a break in the skin. Other routes of infection are by ingesting or inhaling spores. The disease is most common among male cats who prowl in thorny underbrush or sharp prairie grass. Most cases are reported in the northern and central portions of the United States, along river valleys and in coastal areas.
A nodule forms at the site of a skin wound, usually on the feet or legs, the face, or the base of the tail. The hair over the nodule falls out, leaving a moist, ulcerated surface. In some cases there is little surface reaction, but you may see several small firm nodules beneath the skin that appear to form a chain.
This article is excerpted from “Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
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