Ask Elizabeth: What is Cryptococcosis
Q: We recently lost our much loved 2-1/2-year-old cat. He and his mate were originally feral, but with patience and TLC, they became loving pets. It took awhile, but I got their outdoor time down to one-half hour to two hours a day.
But when we took them for their annual examination, I noticed a small swelling on Poppy's underside, and asked the doctor to check it. He said it was just a "fat ball" and was nothing to worry about. Five days later, we took him back because the "fat ball" was growing and had turned dark pink. The doctor suspected it was a bacterial infection and started him on antibiotics, but the swelling continued to grow at an alarming rate over the next several days, turning purple. We returned to the veterinarian, who was shaken. He punctured the swelling, expecting pus to come out, but was surprised to see only dark old blood.
A specialist removed the by-now huge swelling and sent a biopsy to a pathologist. It was not anything we'd ever heard of. It was cryptococcosis. Poppy did not survive.
I later learned that the disease is spread via pigeon droppings. What else can you tell us about this disease?
A: Systemic fungal infections, such as the one your cat had, are caused by the fungi Histoplasma capsulatum, Blastomyces dermatitis, Coccidioides immitis, and Cryptococcus neoformans Generally, they are rare in cats. Infection with Cryptococcus is the most common. A number of reports of cryptococcosis (disease caused by infection with the Cryptococcus fungus) have been published since the early 1950's when the disease was first described in cats.
Cats probably become infected by inhaling the organisms (skin involvement is believed to result when it spreads from other areas of the body, although infection stemming from an injury to the skin is possible). Cryptococcosis can involve many different organ systems - thus, the term systemic - including the skin, the brain and spinal cord, the nasal passages and other parts of the respiratory system, the eyes, the bone marrow, the liver, and the kidneys. More than likely, the mass found under Poppy's skin was just the tip of the iceberg.
As with all the systemic fungal infections, treatment is lengthy, expensive, and often unsuccessful. Preventing infection would be the ideal solution: just keep cats away from places where the fungi are present and all should be okay. Unfortunately, it's not that simple, because the organism is ubiquitous in the environment. It is commonly found in the soil (being a saprophytic, yeast-like fungus that feeds on dead plant and animal material) and even on the skin, in the mouth, and in the gastrointestinal tract of healthy humans-and presumably cats, as well. It's found in highest concentrations in pigeon droppings, where it remains capable of causing infections for at least several years.
Healthy humans, cats, and other species are by nature quite resistant to infection - so resistant, in fact, that if a person becomes infected with the fungus, it always heralds the need to look for some underlying disorder of the immune system (such as AIDS and certain forms of cancer). Upwards of 5-10% of human AIDS patients develop cryptococcosis at some time during their illness because of suppression of their immune system. In some studies, cats with cryptococcosis were more likely to be infected with feline leukemia virus or feline immunodeficiency virus - both of which cause immunosuppressive disorders - than the general feline population. However, underlying disease is usually not found in cats with cryptococcosis, so the reasons why some cats become infected with the organism while the vast majority do not are simply not known at this time.
Prevention of exposure to the fungus is not possible, but it's a good idea to keep cats away from areas where the fungus is likely to be present in high numbers. Avoid areas that have high concentrations of pigeon droppings, especially damp, shaded buildings where the Cryptococcus organism can survive for long periods. Don't worry that you might have become infected from Poppy. Contact with infected pets is not a risk to people.