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Histoplasma capsulatum

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Presentation on theme: "Histoplasma capsulatum"— Presentation transcript:

1 Histoplasma capsulatum
Dipendra Shrestha KDCH

2 Characteristics (cont.)
Dimorphic fungus Mycelium at 25-30º C - Sexual multi-cellular saprophyte, septate, form microconidia and macroconidia Yeast at 37º C - Asexual unicellular intracellular parasite, white, thin walled, oval Mycelial form is most commonly found in the environment Reservoir is soil enriched with droppings of birds or bats Human, many domestic animals, bats are infected by ingestion of spores



5 Pathogenesis Infection begins with inhalation of microconidia or hyphal fragments Mycelial form transforms into yeast form Triggered by elevated temperatures and increased cysteine levels

6 Pathogenesis (cont.) Yeast cells are phagocytized by host immune system H. capsulatum is able to survive phagocytosis Apoptosis of infected macrophages allow H. capsulatum to spread Infection is usually self-limiting in immunocompetent individuals, Cell mediated immunity arises in 15 days

7 Histoplasmosis 2 major forms of histoplasmosis
Pulmonary and disseminated Pulmonary histoplasmosis Conidia or mycelial fragments are inhaled and lodge on the mucous membranes of the respiratory tree or in the alveoli of the lungs, where they encounter macrophages and are phagocytosed. Form lesions in lungs nodes The patient may feel fever, chest pains, a general ill feeling, and a dry cough. Distinct patterns may be seen on a chest x-ray. Chronic lung disease resembles tuberculosis and can worsen over months or years. 

8 Pulmonary Histoplasmosis


10 Pulmonary histoplasmosis
Chronic pulmonary histoplasmosis (1/100,000) pre-existing structural lung defect, i.e. COPD, emphysema (damage of alveoli resulting less O2 supply) chronic pneumonia or infection in cavities, increased sputum reactivation or reinfection Mediastinal granulomatosis and fibrosis Fibrosis, occlusion of mediastinal structure

11 Pulmonary Histoplasmosis
Chronic fibrocavitary histoplasmosis

12 Mediastinal granulomatosis


14 Disseminated Histoplasmosis
Occurs primarily in immunocompromised individuals where H. capsulatum is able to spread from the lungs into other organs Patients display fever, malaise, and occasionally petechiae or skin lesions (cutaneous histoplasmosis) Tests often reveal mucous membrane ulcerations, simultaneous enlargement of the liver and spleen, and enlarged lymph nodes


16 Disseminated Histoplasmosis (cont.)

17 Disseminated Histoplasmosis (cont.)

18 Progressive disseminated histoplasmosis
Defects in host immunity Infants, immuncompromised, HIV Acute, subacute, chronic Failure of macrophages to kill fungus Diffuse spread throughout MPS Oropharyngeal ulcers Hepatosplenomegaly Adrenal GI Endocarditis Meningitis Brain abscess Lymphadenopathy Coagulopathy Bone marrow suppression (pancytopenia)

19 Oral histoplasmosis

20 Diagnosis 1. Obtain appropriate specimens sputum bone marrow
blood lesion scrapings urine biopsy specimens 2. Direct Examination Tissue Specimens stains for fungi – Giemsa, Wright routine histology - H & E - small yeast (2-4 ) intracellular in macrophages - Sputum - KOH or calcofluor

21 Blood Thin smear

22 Calcofluor stain x400 Narrow-neck bud

23 H&E mouth biopsy Yeast in macrophages

24 Giemsa staining of lung biopsy

25 Histoplasmosis (diagnosis cont.)
3. Culture Sabouraud’s agar with cycloheximide and cholramphenicol, 25º C for 2-6 weeks give white cottony mycelium White - brown mould Typical microscopic morphology Mould at RT in SDA

26 Microscopic morphology

27 Microscopic morphology
macroconidia and microconidia

28 Hyphal to yeast conversion at 37ºC
Yeast cells Yeast-like colonies

29 Diagnosis (cont.) Histoplasmin Skin test Serology
Culture filtrate (histoplasmin) is inoculated to observe cell mediated immunity. Serology Complement fixation test Precipitation and agglutination

30 Treatment Treatment is not required in most cases
Itraconazole and/or amphotericin B in more serious cases No effective treatment for fibrosing mediastinitis Amphotericin B Itraconazole

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