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Deep Fungal Infections

cat_long_hair_sittingWhen we think of infections in cats, the common bacteria and viruses come to mind first. Another group of diseases is less well known. These are caused by fungal agents. Some of these fungal diseases that affect cats are regionally distributed.

Here we will introduce you to some of the deep fungal infections.


An uncommon fungal infection, this is more frequently seen in dogs than cats. A few different species of Aspergillus are responsible. These fungi are found everywhere in the environment. Either localized upper respiratory or deep infection that spreads throughout the body can develop. The localized form may invade the sinuses. Cats may also have involvement of lungs or digestive tract. Signs of the upper respiratory infection include sneezing and nasal discharge, while the deep infection produces general signs of malaise, and vomiting and diarrhea. Cats that have chronic virus infections, cancer or diabetes are predisposed to this type of deep fungal infection.


The yeast Candida is a normal part of the surface of the mucous membranes, ears, digestive and reproductive tracts but if the cat becomes immune suppressed due to chronic virus infections, cancer therapy or diabetes, this yeast may be an opportunist and cause disease. Ear, oral cavity, or bladder may become overgrown with Candida causing illness associated with these infected sites. It can also cause pus in the chest.


Much more commonly seen in dogs than cats, the organism Coccidioides is found in soils in the Southwest. It does well in low moisture areas. Lameness, difficulty breathing, eye and skin lesions, poor body condition, and swollen glands may be seen in infected cats. Inhalation is followed by fungal distribution around to the body tissues in about ten days.


The yeast Cryptococcus is found in decaying matter and bird (especially pigeon) droppings across the US , but prevalence of infections is highest in the southern end of California . The infection is much more commonly seen in cats than dogs, with more Siamese cats reported infected than other breeds (it's unknown why). It is the most common deep fungal disease of cats. In cats, the infection usually leads to chronic infections of the nose and sinuses, and skin ulcers. Other organs such as spleen and kidney, and skeletal muscles can be infected too. Usually the organisms are inhaled, and can spread to eyes and brain as well. If that happens, seizures and balance problems, and vision problems may develop. Note that cats may develop a noticeable bump over the bridge of the nose related to inflammation in the tissues there. If a cat has chronic virus infections, the disease will tend to be more serious; it is common to find FeLV infection in cats ill with cryptococcosis.


Much more commonly seen in dogs than cats, this infection is caused by Blastomyces, a soil fungus. The little threads in the soil are inhaled, and turn into a yeast inside the body, which establishes a colony in the deep lung. The bloodstream carries the yeast around to other organs of the body. This disease is regional in distribution, with a higher incidence along the Ohio , Missouri and Mississippi watersheds, in damp areas near rivers and lakes, with richly organic soils. Bat and bird droppings may spread the fungus. Skin lesions, swollen glands, fever, cough and weight loss may occur in infected cats. Serious eye lesions and disorientation may also occur but in cats with normal immune systems, infections are usually contained in the respiratory tract.


The fungus Histoplasma is resident in soil rich in organic materials, especially bird and bat droppings. Old buildings, in places where birds roost can be another site where this organism thrives, and it can be carried a distance in contaminated dust. The spores are inhaled into the lungs. Histoplasmosis is a rare infection in cats. The fungus becomes yeast inside the body and spreads in the bloodstream around to different organs. The Histoplasma can also enter via the mouth/digestive system and set up infection there.

Not all cats become ill, and some just show mild vague signs, but those with chronic virus diseases may develop serious infection due to reduced efficiency of the immune system. An uncommon disease, but in the US it is found in patchy areas throughout most regions except the northwest. Most infected cats are young cats that go outside. Fever, slow weight loss, eye problems, swollen glands, difficulty breathing, anemia, and coughing or lameness are common signs. Some cats may develop diarrhea if the intestine tract becomes infected.

This brief introduction to these fascinating diseases of cats cannot cover all the bases, but hopefully this quick look at some unusual agents will encourage you to ask your veterinary health care team for more information if you live in an area affected by these fungal infections. Some of these deep fungi can infect people from the same sources that infect cats.

Many of these diseases can be treated with anti-fungal medications and supportive care as long as the cat has an immune system that is functioning normally, and the infection has not become too advanced. Some of these fungi develop resistance to the drugs used to manage them, so the veterinarian may have to adjust medications. Some of the anti-fungal medications can have serious side effects in some patients, so liver enzyme monitoring and other tracking tests to assess the patient’s wellbeing may be recommended by the attending clinician. It can take months of treatment to bring these conditions under control.

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