Systemic Fungal Diseases in Pets

The most common fungal diseases we see in small animal practice are those involving the skin such as ringworm (“dermatophytes”), and yeast infections of the skin.  While these are important and need treatment, they seldom make the patient systemically ill.  That is not the case with some other fungal infections.

Dogs and cats may fall victim to infection from a variety of different fungal species. The general term, mycoses, describes infections from fungi species that can attack a healthy pet, as well as opportunistic species that are more likely to infect pets with compromised health. lab-worker-inspecting-petri-dishTypically, a soil-dwelling or airborne fungal organism will invade your pet through ingestion, inhalation or through a skin abrasion. Once they gain entry, these organisms can attack an animal’s mucous membranes and multiple organ systems. While fungal infections are challenging to cure, they often can be controlled with the proper treatment.  Your vet will determine what medication and dosage to prescribe.

The Big Five fungal infections are:

  1. Aspergillosis: This fungal disease is caused by an opportunistic mold that is found in many environments. Dogs with compromised immune systems, due to disease, stress or medication therapies, are vulnerable to the aspergillus fungus. Dogs can breathe in this organism while snuffling soil. Symptoms include nosebleeds, nasal pain, sneezing, swollen nose, nasal discharge and loss of appetite. After several months of spreading through the animal’s body, lameness or spinal pain can appear, as well as vomiting, fever and weight loss. Your veterinarian can treat an aspergillus infection with imitazole antifungal drugs. If the infection is limited to the nasal area, the drug can be directly administered to the nose. Systemic infection is hard to cure.
  2. Blastomycosis: Mainly found in the eastern portion of the U.S., the fungus that causes this infection is commonly found in rotting wood, bird droppings and other organic debris. Pets can become infected by inhaling spores. Symptoms include coughing, pneumonia, lameness, weight loss, and puss-filled nodules on the skin and eyes. Imitazole class drugs are used to treat this infection and reduce symptoms.
  3. Cryptococcosis: Caused by the yeast-like fungus cryptococcus, this fungal infection attacks cats as well as dogs, which acquire it by breathing in spores from bird droppings that contaminate soil. This organism infects the skin, lymph nodes, eyes and brain. Half of the dogs that contract this infection exhibit coughing, nasal discharge and other respiratory symptoms. If brain infection occurs, your pet may experience seizures, blindness, dementia, and troubled walking. Should an eye infection result, it can cause inflammation and blindness. Oral imitazole and other antifungal drugs are effective when administered early, but advanced cases have a poor prognosis.micrograph-fungus
  4. Histoplasmosis: Also called Ohio River Valley Fever, the histoplasma fungus is found in the Midwest, where the soil is nitrogen-rich. Soil becomes infected by the droppings of bats, chickens and other birds. Victims, including humans, breathe in spores of this fungus from the soil. Symptoms are usually mild to moderate and include respiratory and intestine infections that cause diarrhea, vomiting, fever, coughing, muscular atrophy and weight loss. Lymph nodes and tonsils can become enlarged, and other organs can become infected, including the spleen, eyes, skin, liver and brain. Severe infections can be treated with Amphoteracin B in conjunction with an imitazole drug.
  5. Coccidioidomycosis: AKA Valley Fever, this is the most virulent fungal disease in dogs. It is most prevalent in the Southwestern U.S., where conditions are dusty and dry. Infection usually occurs by inhaling spores. Many cases show no symptoms, but aggressive forms attack the lungs and can cause pneumonia, weight loss, persistent cough, fever and lameness, as well as damage to the bones, skin, spleen liver, lymph nodes and brain. Prolonged imitazole treatment may be needed to prevent recurrence, but relapses occur frequently.

There are numerous other fungal species that can infect your pet. Your vet’s lab will perform a microscopic evaluation to identify the exact species, and may also perform additional tests. If your pet shows any unusual symptoms, especially if it has contact with soil that may be contaminated, bring it into your vet and describe the situation. It’s important to catch and treat fungal infections.