Cryptococcosis is a yeast infection that is much more common in cats than in dogs.
Cryptococcus is primarily a pigeon saprophyte (it infects pigeons without making them ill) that is passed in pigeon droppings and may pose an infection risk to mammals.
The symptoms depend on which part of the body the yeast settles in, but they can range from mild snuffles to serious neurological problems such as fits.
The infection is likely to be inhaled, so sneezing and a runny nose are early symptoms.
Other animals develop skin lesions in the form of spots, nodules and discharging sinuses. Cryptococcus also has a nasty habit of invading the eye, which causes blindness and inflammation.
If it spreads to the nervous system, the patient can show neurological symptoms including:
- Head pressing
Cryptococcosis is caused by yeast-like Cryptococcus neoformans. This is a pigeon parasite, but it doesn’t make the pigeon ill because the bird’s high body temperature keeps the yeast in check.
However, Cryptococcus is passed in pigeon droppings, where it can infect mammals that become ill from it because of their lower body temperatures.
Mammals tend to inhale the infection. It passes from their lungs and can travel in the bloodstream to any part of the body. The symptoms differ depending on where the infection localizes, but it can settle in the lungs, central nervous system, nose or even the eye.
There are several avenues to explore when reaching a diagnosis of cryptococcosis, but each has advantages and disadvantages.
One of these is looking for serological evidence of exposure to Cryptococcus. However, the blood test can yield false negatives if the infection is localized to one part of the body and walled off rather than generalized and recognized by the immune system.
Another option is to take samples of infected tissue and examine them under the microscope for the presence of the Cryptococcus organism. This works well in theory, but if the infection is inaccessible, such as in the eye or the central nervous system, collecting the sample poses a problem.
The next best thing is to try and demonstrate the presence of this organism by growing it from small tissue samples.
A number of medications are effective at killing yeast and can be used to treat cryptococcosis. These include:
- Amphotericin B
However, the penetration of these drugs into the tissues where they are needed is quite variable, and these drugs are also associated with a range of side effects including vomiting, diarrhea and kidney damage.
Different drugs are preferred depending on the location of the infection. Thus, for skin, ketoconazole is usually chosen, while itraconazole is a better choice for a central nervous system infection.
Monitoring liver function is advisable during treatment to spot an adverse reaction in a timely manner. Therapy should continue for a couple of months after apparent resolution of the symptoms and is therefore a long-term commitment.
If the infection is in a place that drugs cannot penetrate, such as in the eye, then removal of that eye could be the best remedy.
Because of the strong association of infection being acquired from exposure to pigeon droppings, this should be stopped where possible.
In this video, Dr. Karen Becker, DVM, explains more:
- “Deep mycotic diseases.” Textbook of Veterinary Internal Medicine. 4th edition. Wolf & Troy. Publisher: WB Saunders.
- “Cryptococcosis in dogs: A retrospective study of 20 consecutive cases.” Malki, Dill-Macky, Martin et al. J Med Vet Mycol, 33(5): 291–297.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 13, 2018.