Felis ISSN 2398-2950

Cryptococcus neoformans

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.

Active Forms

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)  ; 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

• Prognosis is poor; long-term therapy required, but often fails, especially if central nervous system disease is present.
• Amphotericin B Amphotericin B.
• Flucytosine Flucytosine.
• Ketoconazole Ketoconazole.
• Itraconazole Itraconazole.
• Fluconazole Fluconazole.

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