Fungi Causing Systemic Mycoses

Question 1

Fungi

Answer 1

> Histoplasma capsulatum

> coccidioides immitis

> Blastomyces dermatitidis

> Paracoccidioides brasiliensis

Question 2

Histoplasmosis capsulatum

Characteristics

Answer 2

> thermally dimorphism (yeast at body temperature & mold in the soil at ambient temperature)

> grows preferentially in soil enriched with bird droppings

> endemic in Ohio & Mississippi River valley areas

Question 3

Transmission

Answer 3

Inhalation of airborne asexual spores (microconidia)

Question 4

Pathogenesis

Answer 4

• micro conduit enter the lung & differentiate into yeast cells
• yeast cells are infested by alveolar macrophages & multiply within them
• an immune response is mounted, granulomas form

Question 5

Disease

Answer 5

Histoplasmosis

Question 6

Microbiological diagnosis

Answer 6

• sputum or tissue can be examined microscopically and culture on Sabouraud’s agar
  > yeasts visible within macrophages

Serologic test for IgM and IgG

Urinary antigen

Question 7

Skin test

Answer 7

• histoplasmin, a mycelial extract, is the antigen
• useful for epidemiological purposes to determine the incidence of infection
• a positive result indicates only that the infection has occurred; it cannot be used to diagnose active disease
• Because skin testing can induce antibodies, serologic tests must be done first

Question 8

Treatment

Answer 8

• amphotericin B for disseminated disease

- Itraconazole for pulmonary disease

Question 9

Prevention

Answer 9

• no vaccine is available

- itraconazole can be used for chronic suppression in AIDs patients

Question 10

Summary

Answer 10

Form in tissue -> location -> clinical findings -> lab diagnosis

Coccidioides:
spherule > SW USA & Latin America > valley fever (disseminated to bone & meninges) > culture at 20oC grows mold with arthrospores; Serologic year for IgM & IgG

Histoplasma:
Yeasts within macrophages > Ohio & Mississippi > cavitary lung lesions; granulomas in liver & spleen > culture at 20oC grows mold with tuberculate macroconidia; serologic tests for IgM & IgG; urinary antigen

Blastomyces:
Yeast with single broad-based bud; central & SE states in USA, Africa > ulcerated lesion of the skin > culture at 20oC grows mold

Paracoccidiodes:
Yeasts with multiple buds > Latin America: Brazil > ulcerated lesions of the face & mouth > cultures at 20oC grows mold; serological tests for IgM & IgG