Fungal Diseases and Yeast Infections

Fungal diseases cause significant mortality in dogs and cats. Blastomycosis, histoplasmosis, coccidiomycosis, and cryptococcosis are the four most common fungal diseases. Unlike cats, which are not known to have any age or breed predispositions, young adult, large breed dogs generally are predisposed to these often fatal diseases.


Blastomycosis is a systemic fungal infection that may involve one or all of the body systems. Blastomycosis is caused by the fungal organism Blastomyces dermatitidis which prefers moist soil enriched with bird or bat droppings. Infection is caused by inhaling fungal spores. The infection mainly occurs around the Mississippi, Missouri, Ohio River Valleys and the Great Lakes.

Common signs are caughing, rapid breathing, pneumonia and fever. In severe cases, there will be loss of weight, loss of appetite, seizures, lameness, eye lesions, and even death. Most cases are diagnosed in the fall. Treatment may be very long, though drugs usually have few side affects. Amphotericin B, ketoconazole, itraconazole, or a combination of some of these drugs have been affective. Sixty to seventy percent of affected animals respond well to treatment. However, if eyes or nervous system is involved, the infection often relapses.

Blastomycosis can be transmitted to humans through an open wound. But, humans can acquire blastomycosis infection in the same way as their pets.


Coccidiomycosis is caused by Coccidiodes immites organisms and seen mainly in the desert regions of the North America. This systemic fungal infection originates in the lungs but may spread to other body systems. Young, male, large-breed dogs seem predisposed. Diagnosis is made based on clinical signs and microscopic identification of the organisms. Treatment is complicated by limited availability of fungicidal antimicrobial medications and the necessity of long-term treatment with expensive drugs.


Cryptococcosis is the most common form of feline fungal disease which occurs either in acute or chronic form. It is caused by a Cryptococcosis neoformans, a yeast-like fungus found in soil contaminated with pigeon and other bird droppings. Cats get infected by inhaling the fungal spores. The disease affects more often cats than dogs and male cats are reported to be affected more often than female cats. At and early stage signs may include sneezing, coughing, snoring, spasmodic swallowing of the air, labored breathing, discharge from the nose and eyes. With the disseminated form of the disease when the fungus spreads over the body, signs may include blindness, circling and movement discoordination. In some cases, the infection involves skin (skin rash or lesion - pinpoint red spots), various tissues, and central nervous system where tumour-like masses called granulomas develop. The fungus is often fatal if it infects the nervous system where it causes an inflammation of the membranes covering the brain and spinal cord (meningitis).


Candida species are medically important fungi. These fungi reside on the skin, mucosa and gastrointestinal tract of 30 to 50% of healthy individuals at any given time, with everyone being colonized at a certain moment of his/her lifetime. Although they are not pathogenic under normal host conditions, they can cause severe mucosal or systemic infections when host defense is compromised, especially in immunocompromised hosts. However, not all individuals at risk develop Candida infections.

The disease is diagnosed based on signs and laboratory analysis of smears collected from the nose or from skin lesions. A complete recovery can only be guaranteed if the affected animal responds well to drug therapy such as itraconazole which is to be applied for several months after the clinical signs disappear. The prognosis for return of vision for eyes affected with fungal disease is still poor. Cats infected with FeLV or FIV are more likely to fail to respond to treatment. Although humans may contract this disease, the diseases does not spread from human to human or animal to animal.


Histoplasmosis is a systemic fungal infection caused by Histoplasma capsulatum organism which grows in bird manure or organically enriched soil. The infection occurs primarily in the Central states and in some Southwest areas of the U.S. Dogs and cats, as well as humans get infected by inhaling contaminated dust.

In humans, the disease is extremely common and will most likely occur while cleaning poultry yards. Some careless cavers also have become seriously ill after inhaling large quantities of dust contaminated with bat droppings while crawling the cave passages or digging for artifacts in bat caves.

Signs are similar to blastomycosis and usually appear from about 10 days after exposure. These may include, diarrhea, weight loss, depression, lameness, coughing and eye and skin changes. The fungal infection starts in the lungs from where it spreads to liver, spleen, gastrointestinal tract, bone and bone marrow, and eyes. The diagnosis is made by identification of the yeast cells in tissue samples. Mild cases of the infection may resolve on their own, but many dogs and cats need extensive treatment to save their lives. Treatment is often effective, especially early in the disease, although it is expensive and long-term, with many animals needing over a year of treatment. Sometimes the treatment must continue lifelong. Eye disease may not respond to treatment even when respiratory and other organ system clinical signs are rapidly improving. Itraconazole is the treatment of choice.

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