Felis ISSN 2398-2950

Cryptococcus neoformans

Synonym(s): C. neoformans

Contributor(s): Stephen Barr, Susan Dawson, Grace Mulcahy

Introduction

Classification

Taxonomy

  • Genus: Cryptococcus.
  • Species: neoformans.
  • Perfect form (serotypes A and D): Filobasidiella neoformans.
  • Perfect form (serotypes B and C): Filobasidiella basillispora.

Etymology

  • Gr: kruptos - hidden; kokkos - grain, berry, seed.

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Clinical Effects

Epidemiology

Habitat

  • Surface dust and dirt.
  • High concentrations in pigeon droppings, which are rich in creatinine and inhibit other organisms.
  • Birds may be subclinical carriers.

Transmission

  • Usually via inhalation from environment.
  • Occasionally percutaneous.

Pathological effects

  • Immunosuppression may predispose to infection; 20-30% of cats with cryptococcosis have feline leukemia virus infection Feline leukemia virus disease.
  • Capsular polysaccharide depletes complement and causes immune paralysis and antibody masking.
  • Antiphagocytic, immunosuppressive capsule   →   encapsulated yeast cells ignored by phagocytes in absence of antibody.
  • Inflammatory response is minimal.
  • Large amounts of free capsular antigen in disseminated disease may depress the humoral immune response and bind antibody, resulting in anitbody titers of zero.
  • With successful treatment levels of antigen fall and antibody titers rise.
  • Cell-mediated immunity (macrophages) dispose of the agent.
  • Virulence is largely associated with the antiphagocytic and immunosuppressive capsule.
  • Route of infection: usually respiratory, resulting in lesions in nasal cavity or sinuses with possible extension to the brain (involvement of the optic nerve causing blindness), and meninges.
  • Due to lack of effective immunity and inflammatory response, colonies grow   →   large myxomatous masses consisting of capsular slime and yeast cells   →   eventually surrounded by histiocytes, epithelioid cells and giant cells.
  • High incidence of nasal lesions (about 50% of cases) Cryptococcosis: whole cat ; some localized skin infections occur.
  • Organisms often disseminate   →   uveal tract, meninges, lymph nodes, lungs, joints, bones and other organs.
  • Often chronic disease: anorexia, wasting and fever.
  • Granulomas of subcutaneous tissue and the nose with possible central nervous system (CNS) involvement in dogs and cats; nasal passage granulomas in horses, mastitis in cattle, respiratory disease and meningitis in humans.
  • Clinical signs depend on location of infection; in cats, most commonly upper respiratory tract.
  • Radiographs of nasal passages show soft tissue proliferation.

Other Host Effects

  • Birds are commonly subclinically infected and can act as reservoir hosts.
  • Human infection often associated with pre-existing immunosuppression.
  • Humans most commonly infected from environmental sources (pigeon feces).

Control

Control via animal

  • Localized lesions may be excized prior to drug therapy.

Control via chemotherapies

Control via environment

  • Disinfect contaminated surfaces with lime solution prior to physical cleaning.
    Masks must be worn.
  • Hydrated lime powder kills the organism.

Vaccination

  • Autogenous bacterins have been used.
  • No commercial vaccines available.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Noxon J O et al (1986) Ketoconazole treatment in canine and feline cryptococcosis. JAAHA 22, 179.
  • Medleau L et al (1985) Cutaneous cryptococcosis in three cats. JAVMA 187, 169.
  • Provost E, McKee J M & Crawford P (1982) Successful medical management of severe feline cryptococcosis. JAAHA 18, 111.
  • Wilkinson G T (1979) Feline cryptococcosis - a review and seven case reports. JSAP 20, 749.

Other sources of information

  • Medleau L (1989) Feline cryptococcosis. In: Current Veterinary Therapy X. Ed R W Kirk and J D Bonagura. Philadelphia: W B Saunders. pp 1109-1112. ISBN 0 7216 2858 3. (A useful overview with North American bias.)
  • Jacobs G J & Medleau L (1998) Cryptococcosis. In: Infectious diseases of the dog and cat. Ed C E Greene. Philadelphia: W B Saunders. pp 383-390. ISBN 0 7216 2737 4.

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