By Dr. Becker
Today I’d like to discuss cryptococcal infections in pets.
Cryptococcus is a relatively common infection caused by a yeast-like fungus called Cryptococcus neoformans. The fungus is widespread in the environment. Cats, dogs, humans, and other animals can become infected. The condition is much more common in cats than dogs, and is primarily a problem in animals that have weak or compromised immune systems.
How Pets Acquire a Cryptococcal Infection
A cryptococcal infection is acquired most commonly by inhaling the infectious spores in bird droppings – in particular, pigeon droppings. The fungus has also been found in soil, fruit, and even in the skin of healthy people. However, the main source of exposure and contamination is pigeon poop.
Pigeons rarely become infected with cryptococcus, because their body temperatures are too high to support the growth of the fungus, which passes through their GI tract and is concentrated in their feces. If the fungus is deposited where it is protected from sunshine and drying out, it can actually survive in the environment for up to two years. Once your cat inhales the spores, the fungus sets up shop in the upper respiratory tract, typically in the nasal passages or the lungs.
In immunologically healthy animals, the fungus remains isolated and doesn’t create any problems at all. But in cats with suppressed immune systems (for instance, those that are dealing with feline leukemia or FIV), the disease can take hold and spread to other organs, including the brain, eyes, lungs, and the central nervous system. This type of disease progression can result in granulomas, pneumonia, or systemic disease.
Cryptococcal infections are not zoonotic, which means they are not spread between humans and animals. The only way to acquire this illness is through direct exposure to the fungal spores themselves.
Symptoms and Diagnosis
Symptoms of cryptococcus vary depending on the organ systems affected by the fungus. Often, symptoms are systemic and nonspecific, such as diminished appetite, weight loss, or lethargy. Other signs to watch for in your cat or dog are sniffling, sneezing, raspy breathing, or a runny nose. Sometimes infected animals can have hard lumpy swellings over the bridge of the nose, skin lesions on the top of the head, or swollen lymph nodes.
If the fungus has invaded the central nervous system, there can be head tilting, nystagmus (a strange, abnormal back and forth eye movement), the inability to blink due to paralysis of the facial nerves, or loss of coordination, including circling and seizures.
Eye problems are also very common and can include hemorrhage in the retina, as well as inflammatory conditions of the eye like chorioretinitis and anterior uveitis.
Diagnosis of a cryptococcal infection can be done quickly and easily through examination of either discharge from the kitty’s nose or skin lesions. The fungus is usually very easy to spot under a microscope and is easily cultured in the laboratory. There’s also a widely used blood test that identifies the fungus, called the latex agglutination test. If a lump is biopsied, diagnosis is made by microscopic examination of the removed tissue.
Once a definitive diagnosis is made, the cat should also receive a complete workup to determine if there’s an underlying disease that has compromised the immune system. Any underlying conditions must be treated in order to successfully treat the cryptococcal infection.
I have personally only seen the infection in immunocompromised animals, so I encourage you to look for an underlying reason for why your pet acquired the infection.