Cryptococcosis

Also known as

European blastomycosis, torulosis

Description

Infection with the yeast Cryptococcus neoformans occurs worldwide in most species of animals, either as a generalized disease or as a granulomatous meningoencephalitis (inflammatory disease of the central nervous system).

Lesions of the nasal mucosa (mucous membrane lining inside the nose) caused by this yeast infection have been seen in horses and cattle.  Enlarged lymph nodes have also been reported in cattle. This yeast can also cause mastitis in cattle, and lung lesions.

Cryptococcosis is a systemic disease that may affect the respiratory tract (especially the nasal cavity), central nervous system, eyes, and skin (particularly skin of the face and neck of cats). The causal fungi are yeasts, Cryptococcus neoformans and C. gattii, which exist in the environment. They are commonly found in soil and fowl feces, especially in pigeon droppings.

Transmission is by inhalation of spores or contamination of wounds. In bird droppings, the microscopic spores may contaminate soil or organic debris. They may be inhaled into the deeper portions of the lungs when an animal breathes contaminated dust.

Cryptococcosis is most common in cats but also is seen in dogs, cattle, horses, sheep, goats, birds, and wild animals. In humans, many cases are associated with a defective cell-mediated immune response.

Cryptococcosis has also been associated with mastitis, and many cows in a herd may be infected. The affected cows have poor appetite, decreased milk flow, swelling and firmness of affected quarters, and enlarged lymph nodes above the udder.

Signs

• Soft swellings inside the nose,
• Mastitis,
• Poor appetite,
• Hard swelling in udder,
• Enlarged lymph nodes above udder

Cause

The genus Cryptococcus includes multiple yeast species, most of which are saprophytes (living on dead or dying organisms in the environment) that do not cause infections in humans or animals.

The pathogenic agents of cryptococcosis are classified into two species, C. neoformans and C.gattii. These have several sub-types that vary in geographic distribution and susceptibility to anti-fungal drugs.

Disease caused by other Cryptococcus species, such as Cryptococcus laurentii and Cryptococcus albidus, have been reported less frequently and generally occur only in immunocompromised hosts.

Cryptococcus neoformans infections have been reported in a wide variety of animals from lower invertebrates such as soil dwelling amebae, nematodes, cockroaches, and mites, to mammals. Cats are the most frequently infected animals, with involvement of the upper and or lower respiratory tract.

They may also have subcutaneous masses of granular tissue, and spreading infection. Dogs may have similar signs but central nervous system involvement is more common. Cryptococcosis has been known to cause mastitis in dairy animals and respiratory infections in horses.

Household rodents may serve as a continuous source of infection for humans and pets. Rodents, especially rats and mice, have expanded their geographic range dramatically and significantly extended the territory of harbored pathogens.

Rodents may be natural reservoirs, alternate hosts, sentinel animals, carriers, and passenger hosts of various fungi and yeasts.

Prevention

It is difficult and often impossible to prevent yeast infections since they are always present in the environment. The best means of prevention is to decrease animals’ contact with areas containing a high concentration of yeast organisms, such as pigeon droppings, damp buildings or barns.

Treatment

Fluconazole or itraconazole are considered the treatments of choice. Flucytosine can be used alone, but drug resistance may develop with this product, so combination therapy with amphotericin is usually recommended.

In cattle, Amphotericin B, ketoconazole, itraconazole and fluconazole are effective but expensive and usually reserved for valuable cattle.

Outcomes of treatment are varied. Drug therapy is long-term (average of 8.5 months) and relapses occur frequently. Severe affected cattle are usually culled.