Felis ISSN 2398-2950

Cryptococcosis

Synonym(s): Cryptococcus neoformans disease

Contributor(s): Vanessa Barrs

Introduction

  • Cause: Cryptococcosis (Cryptococcus neoformans Cryptococcus gattii species complex) is caused by a dimorphic fungus that can grow as a mold in the environment and as a yeast at the higher temperatures within the tissues of infected hosts.
  • There are 4 major molecular types of C. neoformans (VNI-VNIV) and C. gattii (VGI-VGIV) with subdivisions in VGII and III (VGIIa-c, VGIIIa-b).
  • Differences in species and molecular type are associated with differences in clinical presentation.
  • Organisms usually colonize the upper respiratory tract after inhalation of the infectious propagules known as basidiospores. 
  • Most common systemic fungal disease in cats (more common in cats than dogs).
  • Signs: clinical presentation depends on the stage of disease at which diagnosis occurs, and is also influenced by host species and molecular type of the organism.
  • In early disease upper respiratory signs predominate. Infection can remain localized within the sinonasal cavity or can extend to involve paranasal tissues including the CNS via breach of the cribiform plate (meningoencephalitis); along the optic nerve (optic neuritis/chorioretinitis); into the lower respiratory tract; or can disseminate hematogenously to any organ (eg lymph nodes, skin, CNS, abdominal organs). Once hematogenous spread occurs, multiple organs can be affected, especially the CNS).
  • In cats, presentation for upper respiratory tract (URT) signs is most common, sometimes with additional signs related to local invasion of tissues contiguous with the URT.
  • In dogs, dissemination of disease occurs early and presentation for CNS and/or ocular signs is most common overall.
  • Feline leukemia virus (FeLV) Feline leukemia virus or feline immunodeficiency virus (FIV)  Feline immunodeficiency virus disease infections are not over-represented amongst affected cats.
  • Prognosis: prognosis for feline cryptococcosis overall is good.
  • CNS involvement is a negative prognostic indicator in both feline and canine cryptococcosis.
  • The prognosios for canine cryptococcosis is poor overall compared to cats, and in addition to CNS involvement, is influenced by the cryptococcal strain and host immunity.
  • Treatment: antifungal therapy.

Pathogenesis

Etiology

  • Cryptococcus neoformans Cryptococcus neoformans - Cryptococcus gattii species complex.
  • Saprophytic, budding yeast (1-7 micrometres) with polysaccharide capsule.
  • Capsule prevents desiccation in soil.

Predisposing factors

General

  • Cryptococcus spp causes disease in immunocompetent cats and dogs, and is more common in cats than in dogs.
  • Over-represented feline breeds in some studies include Siamese Siamese, Birman Birman and Ragdolls Ragdoll.

Specific

  • Theoretically, contact with pigeon droppings could predispose to C. neoformans infection, although this is rarely reported in practice and other important environmental niches exist.
  • Note that lack of exposure to outdoors does not rule out infection since a quarter of cases in the US occur in indoor cats and C. gattii is easily disseminated in air and water.

Pathophysiology

  • Spores (basidiospores) becomes aerosolized  →  colonize upper respiratory tract (nasal cavity and sinuses) of host  →  remains confined to URT or invades adjacent tissues, eg nasal bridge or CNS through cribiform plate or disseminates to other organs, eg skin, eyes, CNS, lumph nodes.
  • Immunosuppression may favor dissemination.

Timecourse

  • Gradual onset of signs.

Epidemiology

  • Virulence and disease factors are correlated with molecular subtype.
  • Cryptococcus neoformans var grubii (VNI) is the most common cause of cryptococcosis in dogs in the USA (except for the Pacific Northwest) and of dogs and cats overall in Australia.
  • The prevalence of C. gattii infections varies greatly with geographic region. Following an outbreak of disease in humans and animals in the late 1990s C. gattii (VGII) is now endemic in British Columbia in Canada, and in the Pacific Northwest of the USA, and is the most common cause of disease in these regions regardless of host species.
  • C. gattii (VGIII) is the most common cause of crytococcosis in cats in the US overall, with most cases being identified in California, and cause approximately half of infections in cats and dogs in Western Australia (mostly VGII).
  • In Southeastern Australia C. gattii isolates from dogs and cats are predominantly VGI.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Pennisi M G, Hartmann K, Lloret A et al (2013) Cryptococcosis in cats: ABCD guidelines on prevention and management. J Feline Med Surg 15 (7), 611-8 PubMed.

Other sources of information

  • Sykes J E & Malik R (2014) Cryptococcosis. In: Canine and Feline Infectious diseases. Ed J E Sykes, St Louis, Missouri, p 599.


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