Dealt the lowest hand in life's grand plan, single-celled fungi cryptococcus (C. neoformans) — in Greek, "crypto," means concealed or secret — are doomed to an existence hidden deep within the soil and excrement — most notably, pigeon guano — and are alive and infectious for up to two years.
These pathogenic poop-dwellers are the vectors of a severe, systemic, fungal disease known as cryptococcosis in dogs, cats, and their people. Feasting on decomposing vegetation and dead material (saprophytic), these ghoulish, yeastlike fungi are also found in fruit, and, surprisingly, even on the skin of healthy people. Cryptococcus microorganisms are less common in dogs than cats, and are particularly dangerous to immunosuppressed animals. Although generally associated with eucalyptus trees, cryptococcus is found worldwide, and in addition to Australia, some areas of southern California and Canada are prone to the fungus.
How does cryptococcus fungi infect a dog's body?
Introduced via inhalation of its infectious spores through the nasal cavity or entering through a wound, cryptococcus invades the respiratory system where it creates granulomas or lesions that travel throughout the body attacking the central nervous system, skin, digestive system, eyes, lymph nodes, bone, muscle, heart, and other organs. An infection will manifest in respiratory disease, altered mental state, loss of mobility, and seizures. Once clinical signs present, veterinary care should be sought at once, since the chance of recovery is significantly reduced and mortality is high once the fungi affect the central nervous system.
Clinical signs and symptoms of cryptococcosis in dogs.
Some dogs may show vague or nonspecific symptoms such as lethargy. Depending on the stage of infection, the symptoms of cryptococcosis will vary and can include any of the following clinical signs of illness:
- Nasal granuloma which presents as lesions in the nasal cavity.
- Ulcerous abscesses or lesions on the nose.
- Upper respiratory tract disease.
- Lung granuloma or lesions on the lungs.
- Swollen lymph nodes.
- Subcutaneous masses or lipomas.
- Mucous and pus discharge from the nose.
- Bleeding nose
- Head tilt.
- Noisy breathing
- Meningoencephalitis, or inflammation of the brain and meninges, which are three layers of protective tissue called the dura mater, arachnoid mater, and pia mater that surround the neuraxis or central axis of the nervous system.
- Altered mental state.
- Behavioral changes.
- Incoordination or loss of mobility.
- Pain in the neck.
- Diminished appetite, weight loss or anorexia.
- Lesions on the eye.
- Eyeballs bulging out.
- Systemic lesions throughout the body affecting various systems.
How do veterinarians diagnose cryptococcosis?
If you see any symptoms of cryptococcus infection in your dog, you should seek veterinary care as soon as possible. And at the first onset of symptoms, begin keeping notes which will help your vet in her diagnosis. Let her know as well your dog's recent activities and if he's been around bird droppings, or been digging in the dirt outside. A review of your dog's medical history and a complete physical examination will determine whether cryptococcosis is a possibility.
If the vet suspects cryptococcus infection, tissue samples will be taken and a cytologic exam of nasal and skin cells, eye cells, joint fluid, and tissue, including a gram stain of the tissue using crystal violet stain to visualize the organism. If these tests result in a false negative or no organisms are seen, lesions may be biopsied and tested. Lesions within the body are seen in thoracic X-rays or CT scans.
Another diagnostic tool that may be used is a latex agglutination test which detects cryptococcus in serum, urine or cerebrospinal fluid. The results of this test often determine the course of therapy.
Treatment protocol for cryptococcus infection.
If your dog is exhibiting neurological symptoms, he will be admitted to the hospital for supportive care. Otherwise, the infection is primarily treated with a combination of antifungal drugs for six-to-12 months, after which the cryptococcus will begin to die. If the nervous system is affected, glucocorticoids may also be prescribed which improves the dog's prognosis and survival rate if used within the first 10 days. Drugs are chosen based on which bodily systems are affected and may need to be adjusted since some strains of the organism are resistant to some drugs. The most common and successful course of antifungal therapy is with azole drugs which also alleviate the inflammation and edema in the nervous system caused by the dying organisms.
Surgery may be required to remove subcutaneous abscesses and internal masses followed by a course of antifungal therapy.
Prognosis and recovery from cryptococcosis.
Sadly, if your dog has a preexisting immunosuppressive condition or if the disease has progressed beyond a mild infection, the prognosis for recovery is poor. When the organism attacks the central nervous system, death may be the outcome. One study on the disease in dogs found that more than half of those with systemic infection had to be euthanized.
On the other hand, if the disease has not taken hold of the nervous system, your dog may be prescribed antifungal medication for you to administer at home with follow-up monitoring by the veterinarian. In one study of the disease, 24 percent of dogs survived and were in recovery after three to 13 months of treatments.
Further, if surgery was performed, you may need to change bandages, keep the wound clean, administer antibiotics, topical ointments, and pain medication.
How can I prevent my dog from getting a cryptococcus infection?
Keep in mind that cryptococcosis is not a zoonotic disease, therefore your dog is not a health risk and cannot transmit the disease to you or other people.
The key to the prevention of cryptococcus infection is to ensure your dog does not have access to sources of contamination. Keep him away from pigeon lofts and any areas where large flocks of birds, especially pigeons, are prevalent.