Cryptococcosis is most commonly caused by two species of the genus Cryptococcus, C neoformans and C bacillisporus.

In cats, infections with feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) have been thought to predispose to cryptococcosis. However studies have suggested it is a co-infection rather than a secondary infection.

Predisposition towards development of cryptococcosis in Siamese, Birman and Ragdoll cats are significantly over represented amongst reported cases.

Cytologic examination of nasal or cutaneous exudates / masses demonstrates organisms in most cases but in cases where the disease is systemic CSF or ocular fluid can harvest organisms.

Urine sediment should be evaluated because many dogs and the occasional cat can have subclinical renal infection.

Encapsulate organisms like the picture above are easily seen on regular diff quick and rapid staining methods but PAS stains highlight the cytoplasm - but note the capsule does not stain unlike most other yeasts and fungi.

Unencapsulated organisms may be overlooked unless a large number are present.

First published: Wed, Oct 6 2010