Canis ISSN: 2398-2942

Cryptococcosis

Contributor(s): Stephen Barr, Vanessa Barrs, Rosanna Marsella, Bryn Tennant

Introduction

  • Cause: cryptococcosis (Cryptococcus neoformans Cryptococcus neoformans -Cryptococcus gattiispecies 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 ofC. neoformans(VNI-VNIV) andC. 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 dogs, dissemination of disease occurs early and presentation for CNS and/or ocular signs is common overall.
  • Diagnosis: clinical signs and serology.
  • Treatment: fluconazole, itraconazole, amphotericin B.
  • Prognosis: poor overall compared to cats, and in addition to CNS involvement, is influenced by the cryptococcal strain and host immunity.

Pathogenesis

Etiology

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

Predisposing factors

General
  • Cryptococcusspp causes disease in immunocompetent cats and dogs, and is more common in cats than in dogs.
  • Dogs with an active, outdoor lifestyle are thought to be at increased risk of environmental exposure, as reflected by over-representation of medium and large breed dogs in Australian studies.
  • American Cocker spaniels were over-represented in some US studies.

Specific

  • Theoretically, contact with pigeon droppings could predispose toC. neoformansinfection, 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 andC. gattiiis easily disseminated in air and water.

Pathophysiology

  • Spores (basidiospores) becomes aerolized → 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 hematogenously to other organs, eg skin, eyes, CNS, lymph nodes.
  • Immunosuppression may favor dissemination.

 

Timecourse

  • Gradual onset of signs.

Epidemiology

  • Virulence and disease factors are correlated with molecular subtype.
  • C.neoformansvargrubii(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 ofC. gattiiinfections varies greatly with geographic region. Following an outbreak of disease in humans and animals in the late 1990sC. 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 cryptococcosis in cats in the US overall, with most cases being identified in California, and causes approximately half of infections in cats and dogs in Western Australia (mostly VGII).
  • In Southeastern AustraliaC. gattiiisolates 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.
  • Malik R, Hunt G B, Bellenger C R, Allan G S, Martin P, Canfield P J & Love D N (1999) Intra-abdominal cryptococcosis in two dogs. J Small Anim Pract 40 (8), 387-391 PubMed.
  • Malik R, Speed B R, Kaldor J, Cairns B, Pegorer M, Wigney D I & Love D N (1999) Serum antibody response to Cryptococcus neoformans in cats, dogs and koalas with and without active infection. Med Mycol 37 (1), 43-51 PubMed.
  • Tiches D, Vite C H, Dayrell-Hart B, Steinberg S A, Gross S & Lexa F (1998) A case of canine central nervous system cryptococcosis - management with fluconazole. JAAHA 34 (2), 145-151 PubMed.
  • Malik R, Wigney D I, Muir D B &, Love D N (1997) Asymptomatic carriage of Cryptococcus neoformans in the nasal cavity of dogs and cats. J Med Vet Mycol 35 (1), 27-31 PubMed.
  • Malik R, McPetrie R, Wigney D I, Craig A J &, Love D N (1996) A latex cryptococcal antigen agglutination test for diagnosis and monitoring of therapy for cryptococcosis. Aust Vet J 74 (5), 358-364 PubMed.
  • Malik R, Dill-Macky E, Martin P, Wigney D I, Muir D B &, Love D N (1995) Cryptococcosis in dogs - a retrospective study of 20 consecutive cases. J Med Vet Mycol 33 (5), 291-297 PubMed.

Other sources of information

  • Syles 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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