Respiratory Infections III (Updated)

8/7/2019 Respiratory Infections III (Updated)

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Respiratory infections III

Fungal = Systemic mycoses

y Generally result from inhalation of air-borne spores in soil or plant material

y Most are caused by dimorphic fungi

- Saprophytic, vegetative mycelia form in nature and under ordinary laboratory conditions

- Pathogenic, unicellular yeast-like or spherule form in human and animal host tissues

y True pathogens

- Coccidiodomycosis

- Blastomycosis

- Histoplasmosis

- Paracoccidioidomycosis

y Opportunistic pathogens

- Aspergillosis

- Systemic candidosis

- Cryptococcosis- Pneumocystis infection

- Zygomycosis (mucormycosis)

- Others

INCIDENCE

y Systemic mycoses occur most frequently in those who work in the

- Agricultural sector

- Construction industry

y Before (I.e before the antibiotic era and the subsequent development in medicine) =

Systemic mycoses was very rare- Even though known since the end of 19

thcentury

y Often discovered post mortem

y However, since the advent of:

- Antibiotics (mid 1940s)

- Corticotherapy (1950s)

- Immunosuppressive therapy (1960s)

- Catheterization

- Prosthetic devices

- Organ and tissue ttranspolantation

- HIV/AIDS (late 1970s)

y Systemic mycoses started to:

- Develop new clinical aspects

- Occur with much higher frequency

- Begin to become important public health problems

y In fact several opportunistic infections have become nosocoial, hospital-acquired and

invasive infections.

HISTOPLASMOSIS



y Causative organism = H.capsulatum

y Taxonomically H.capsulatum divided into 3 varieties; each with its own distinctive & defining

characteristics

a. H. capsulatun var. capsulatum

- Causes histoplasma capsulate

- Cosmopolitan endemic in all continentsb. H. capsulatum var. duboisii

- Causes histoplasma duboisii

- Liited to central Africa and Madagascar

- Also called African histoplasmosis

c. H. capsulatum var, farciminosum

- Causes histoplasmosis

- Africa, East Europe, Middle East, Asia, Far East

y All 3 varieties are:

- Saprophytes

- Mitosporic moulds (fungi imperfecti) in nature or in laboratory at 25-30 C

- Transformed into unicellular yeast-like budding organisms

- In mammalian tissue

- At 37 C in enriched media with cysteine in lab

Histoplasma Capsulati

y Genus histoplasma established 1906 when Darling described first case

y Usually either an asymptomatic or relatively mild and self-limiting pulmonary infection

y But can be

- Chronic

-

Acute disseminated

y Causative organism: fungus imperfecti histoplasma capsulatum var. capsulatum

- An intracellular parasite

- Found in soil enriched with bird and bat droppings (saprophyte)

- Infection, inhalation of spores

- Cosmopolitan [in USA Mississippi & Ohio river valleys (prevalence: 95%)]

- Mould: fluffy, white or buff brown

- Mycelium: Septate

- 2 types of unicellular asexual spores:

Macroconidia (8-14 micrometer)

Microconidia (2-4 micrometer)

- Yest phase cell 2-3 x 3-4 mucrometer

y Note: In birds not known to be infected. Only transitory infection in chicken (Gallus gallus)

and Pigeon (Columbia livia)

Pathogenesis

y Infection usually asymptomatic or mild (skin test +)

y Sometimes: acute influenza like

y Fever with non-productive cough



y Although self-limiting, patient usually left with discrete, CALCIFIED lesions in the lungs

y Chronic form: usually in adults develop large cavities directly from primary lesions or

reactivation of old lesions (c.f TB)

y Occasionally patient develops acute PROGRESSIVE form with

- Widespread infection of RES

- Diseemination to other organs:- Joints arhtralgia/arthritis

- Skin erythema nodosum & erythema multiforme

- Heart pericarditis

- Liver }

- Renal } failure -> death

- Respiratory }

- Meningitis, cerebritis or focal brain lesion

y Usually in old aged, infancy and immunocompromised

Histoplasmosis(continued)

LABORATORY DIAGNOSIS

y Microscopy

- Sputum (Wright or Giemsa stain)

- Pus (Wright or Giemsa stain)

- Blood smear may be (+) especially in HIV cases

y Biopsy

- PAS stain

- Methenamine-silver stain

[H. capsulatum: small oval teast cells packed within microorganisms and/or monocytes

y Culture: Sabourauds agar

- 25-30 C for 1-4 weeks -> mycelium

- Macro and microconidia visible under microscope

- 37 C in cysteine rich medium -> Yeast form

y Serology

- Precipitation test

- Complement fixation test (CFT)

- Latex particle agglutination test (LPA)

- ELISA

TREATMENT

y Mild

- Ketaconazole

- Itraconazole

y Severe



- Amphotericin B (disseminated, HIV/AIDS patients)

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Respiratory Infections III (Updated)