Transcript

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SYSTEMIC MYCOSES

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Systemic mycoses

Systemic fungal infections are uncommon

Natural immunity is high; physiologic barriers include:

1. Skin and mucus membranes

2. Tissue temperature - fungi grow better at less than

37°C (mesophiles)

3. Redox potential - in vivo conditions too reducing for

most fungi

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Infection requires a large inoculum and is affected by the resistance of the host

• infection often occurs in endemic areas

• most infections are asymptomatic or self-limiting

• in immune-compromised hosts, infections are more often fatal (distinction between infection and disease)

Systemic fungal disease is most often associated with four organisms

1. Coccidioides immitis

2. Histoplasma capsulatum

3. Blastomyces dermatitidis 4. Paracoccidioides brasiliensis

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COCCIDIOIDOMYCOSIS

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Coccidioidomycosis (Vally fever)

• Coccidioides immitis is considered to be the most virulent of fungal pathogens.

• Restricted to hot, semi-arid areas of SW USA and Mexico.

• Grows in the soil, but inhalation of a single spore can initiate infection.

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In infected tissues, C. immitis

appears as a mixture of hyphae and

spherules.

Conidia

Spherules

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Coccidioidomycosis: Normally a benign, sub-

clinical upper respiratory infection

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In a small percentage of cases, organism disseminates

from the lungs to a variety of organs, particularly the

CNS, meanings, skin, soft tissues, and bone.

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In infected tissues, organism is seen as a mixture of

spherules and endospores.

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COCCIDIOIDOMYCOSIS • This is primarily an infection of the lungs caused by

Coccidioides immitis and C. posadasii, two closely related

dimorphic fungi found in the soil of semi-arid regions

• In culture and in soil Coccidioides grows as a mould,

producing large numbers of barrel-shaped arthroconidia,

which are easily dispersed in wind currents.

• In the lungs the arthroconidia form spherules which contain

numerous endospores. Endospores are released by rupture

of the spherule wall and develop to form new spherules in

adjacent tissue or elsewhere in the body.

• In culture the mould colonies are initially moist and white but

change within 5–12 days to become floccose and pale grey

or brown.

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Epidemiology of COCCIDIOIDOMYCOSIS

• Infection is acquired by inhalation; the incubation

period is 1–3 weeks. The major risk factor for infection is

environmental exposure.

• Outbreaks have been associated with ground-disturbing

activities, such as building construction and

archaeological excavation, as well as with natural

events that result in the generation of dust clouds, such

as earthquakes and dust storms.

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1. Race: Filipinos > African American> Caucasian

2. Age: Extremes more susceptible

3. Sex: Males more susceptible

4. Pregnancy

5. Immunosuppression

Risk factors for disseminated

coccidioidomycosis

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Microscopical appearance of

Coccidioides arthroconidia(4 × 6

μm diameter)

Microscopical appearance of Coccidioides

spherules in tissue (up to 120 μm in

diameter)

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Clinical features of COCCIDIOIDOMYCOSIS

• Coccidioides causes a wide spectrum of disease, ranging

from a transient pulmonary infection that resolves without

treatment, to chronic pulmonary infection, or to more

widespread disseminated disease.

• About 40% of newly infected persons develop an acute

symptomatic and often severe influenza-like illness.

• most otherwise healthy persons recover without treatment,

their symptoms disappearing in a few weeks. In some cases

primary infection may result in chronic pulmonary disease.

• Fewer than 1% of infected individuals develop disseminated

coccidioidomycosis. This is a progressive disease that

usually develops within 3–12 months of the initial infection,

although it can occur much later following reactivation of a

quiescent infection in an immunosuppressed individual.

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• One or more sites may be involved, but the skin, soft

tissue, bones, joints and the central nervous system are

most commonly affected.

• Meningitis is the most serious complication of

coccidioidomycosis, occurring in 30–50% of patients with

disseminated disease. Without therapy, it is almost always

fatal.

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Diagnosis

1. Suppurative or granulatomas inflammation

2. Microscopical examination of sputum, pus and biopsy material (Spherule or endospores seen on pathology)

3. Culture of microorganisms

4. Complement fixation assay (in cerebrospinal fluid)

5. Serological tests

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Laboratory diagnosis • Microscopical examination of sputum, pus and biopsy material is helpful

as the relatively large size and numbers of mature spherules present makes their detection and identification comparatively straightforward.

• Material for culture should be inoculated on to screw-capped slopes of Sabouraud agar and incubated at 25–30°C for 1–2 weeks. The fungus can be identified by its colonial morphology and the presence of numerous thick-walled arthroconidia formed in chains from alternate cells of the septate hyphae.

• The arthroconidia are highly infectious and are a serious danger to laboratory staff. Consequently, Petri dishes should never be used for isolation of the organism and all procedures should be carried out in a biological safety cabinet under Category 3 containment.

• Preparations for microscopy should be made only after wetting the colony to reduce spore dispersal.

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• Serological tests play an important part in diagnosis.

• The immunodiffusion test is most useful for detection of early primary infection or exacerbation of existing disease; antibodies appear 1–3 weeks after infection but are seldom detectable after 2–6 months, or in patients with disseminated coccidioidomycosis.

• The latex agglutination test gives similar results to the immunodiffusion test, but is less specific. Complement fixing antibodies appear 1–3 months after infection and persist for long periods in individuals with chronic or disseminated disease.

• In most cases the titre is proportional to the extent of infection; failure of the titre to fall during treatment of disseminated coccidioidomycosis is an ominous sign.

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Treatment

• The historical standard of treatment is intravenous

amphotericin B, but oral fluconazole is now used to treat

many patients with skin, soft tissue, bone or joint

infections. Itraconazole is also effective, but less well

tolerated. Because oral fluconazole is so much more

benign than intrathecal amphotericin B, it is now the drug

of choice for coccidioidal meningitis.

Amphotericin B, Fluconazole

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HISTOPLASMOSIS

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Histoplasmosis (also called cave disease)

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Caused by the dimorphic fungus Histoplasma capsulatum

Tuberculated macroconidia,grown at 25C Intracellular yeast at 37°C

Histoplasmosis is characterized by intracellular growth of the

pathogen in macrophages and a granulomatous reaction in

tissue. These granulomatous foci may reactivate and cause

dissemination of fungi to other tissues.

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Microscopical appearance of Histoplasma

capsulatum microconidia and macroconidia

Microscopical appearance of Histoplasma

capsulatum yeast cells in tissue.

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Histoplasmosis

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1.Usually, acute benign respiratory disease

2.Rarely, progressive, chronic or disseminated disease

3.Endemic area in U.S. -Atlantic Ocean to N. Dakota (500,000 cases/year in U.S.), except New England & Florida. Most cases in Ohio and Mississippi Rivers)

• Other endemic regions include parts of Africa, Australia, India and Malaysia.

H. capsulatum grows in soil.

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More Histoplasmosis

1. Disseminated histoplasmosis is diagnosed frequently in patients with

AIDS living in the central U.S.

2. It is often the initial manifestation of immunodeficiency.

3. In these cases, the organism spreads via blood from the lung to

involve bone marrow, liver, spleen, or skin.

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90% of histoplasmosis cases are clinically

insignificant

HISTOPLASMOSIS

• This disease is caused by H. capsulatum, a dimorphic fungus found in soil enriched with the droppings of birds and bats.

• H. capsulatum var. duboisii is restricted to the continent of Africa.

• H. capsulatum var. capsulatum grows in soil and in culture at 25–30°C as a mould and as an intracellular yeast in animal tissues.

• The small oval yeast phase cells (2–4 μm diameter) can also be produced in vitro by culture at 37°C on blood agar or other enriched media containing cysteine.

• In culture the mould colonies are fluffy, white or buff-brown; the mycelium is septate and two types of unicellular asexual spores are usually produced: large round, tuberculate macroconidia (8–15 μm in diameter) are most prominent and are diagnostic, but smaller, broadly elliptical, smoothwalled microconidia (2–4 μm in diameter) are also present in primary isolates.

• H. capsulatum var. duboisii is morphologically identical to H. capsulatum var. capsulatum in its mycelial phase, but the yeast phase has larger cells (10–15 μm in diameter).

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Epidemiology

• Infection results from the inhalation of spores; the incubation

period is 1–3 weeks.

• Most reported outbreaks have been associated with exposures

to sites contaminated with H. capsulatum or accumulations of

bird or bat guano, such as building demolition, soil excavation

and caving.

• The most serious disseminated forms of the disease are more

common among individuals with underlying cell-mediated

immunological deficiencies, such as persons with HIV infection,

transplant recipients, and those receiving immunosuppressive

treatments or infants.

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Clinical features of HISTOPLASMOSIS

• There is a wide spectrum of disease, ranging from a transient pulmonary infection that subsides without treatment, to chronic pulmonary infection, or to more widespread disseminated disease.

• Many healthy individuals develop no symptoms when exposed to H. capsulatum in an endemic setting. Higher levels of exposure result in an acute symptomatic and often severe flu-like illness, with fever, chills, non-productive cough and fatigue. The symptoms usually disappear within a few weeks, but patients are frequently left with discrete, calcified lesions in the lung.

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• Disseminated histoplasmosis may range from an acute illness that is fatal within a few weeks to immunocompromised patients.

• Hepatic infection is common in nonimmunosuppressed individuals and adrenal gland destruction is a frequent problem. Mucosal ulcers are found in more than 60% of these patients; central nervous system disease occurs in 5–20% of patients.

• The clinical features of H. capsulatum var. duboisii infection

differ from those of var. capsulatum infection.

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Diagnosis • Histology

• culture

• Skin test for histoplasmin [the major hyphal antigen] is not useful, because most people are positive in endemic area.

Laboratory diagnosis H. capsulatum is seen as small, oval yeast cells, often within macrophages

or monocytes .

Microscopy of smears of sputum or pus should be stained by Giemsa

procedure.

Blood smears may be positive for H. capsulatum, especially in persons with

AIDS.

Liver or lung biopsies stained with periodic acid–Schiff or Grocott–Gomori

methenamine–silver.

Specimens should be cultured on Sabouraud agar at 25–30°C to obtain

the mycelial phase. Mycelial colonies develop within 1–2 weeks but

cultures should be retained for 4 weeks before discarding. The fungus is

identified by its colonial morphology and the presence of the characteristic

macroconidia and microconidia.

• Culture at 37°C for the yeast phase is not used for primary isolation,

although conversion from the mould to yeast phase is useful to

confirm the identity of isolates.

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• Mould cultures of H. capsulatum are a hazard to

laboratory staff and consequently screw-capped

slopes rather than Petri dishes should be used for

isolation.

Serological tests are useful, but cross-reactions can occur, mainly

with Coccidioides.

• Antibody tests fail to detect antibodies in up to 50% of

immunosuppressed individuals.

• Tests for antigen detection in the urine by ELISA are useful in

disseminated histoplasmosis but are not widely available outside the

USA.

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Treatment

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• Intravenous amphotericin B is recommended for treatment of the

most severe forms of disseminated histoplasmosis.

• Ketoconazole or itraconazole is effective as therapy for self-

limited disease (used in AIDS).

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BLASTOMYCOSIS

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Blastomycosis Granulomatous mycotic infection that

predominantly involves lungs and skin; but can spread to other organs. Most prevalent in males 40-60 years of age and children.

Blastomyces dermatitidis

Dimorphic organism originates in the

soil and infection ensues by

inhalation of spores. Converts to

yeast in animal hosts or at 37o in

vitro.

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Blastomycosis • Encounter: Most cases are in southern, central, and

southeastern USA. Infection is by inhalation of spores. • Spread: The pulmonary infection is either self -limited or

progressive. Dissemination often occurs to the skin and to the bone - 80% of patients have large skin lesions; a large number also have granulomatous pulmonary lesions.

• Risk Factors: Occupational contact with soil; owning a dog. Living in endemic area.

• Diagnosis: based on clinical findings and microscopic detection of organisms in tissue specimens

33 Microscopical appearance of Blastomyces dermatitidis

yeast cells in tissue, showing broad-based budding.

BLASTOMYCOSIS • This disease is caused by B. dermatitidis, a dimorphic soil-inhabiting fungus. The

largest number of cases of blastomycosis has been reported from North America,

but the disease is also endemic in Africa, and parts of Central and South America.

In the USA,

• the organism is most commonly found in states surrounding the Mississippi and

Ohio Rivers; in Canada, the disease occurs in the provinces that border the Great

Lakes.

• In culture at 25–30°C B. dermatitidis grows as a mould with a septate mycelium.

The colony varies intexture from floccose to smooth and from white to brown in

colour. Asexual conidia are produced on lateral hyphal branches of variable length;

the oval or pear-shaped conidia are 2–10 μm in diameter. In tissue and in culture at

37°C the fungus grows as a large round yeast (5–15 μm in diameter) that

characteristically produces broad-based buds from a single pole on the mother cell.

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Epidemiology

• Infection results from inhalation of spores; the incubation period is 4–

6 weeks. The disease is more commonly seen in adults than in

children, and often occurs in individuals with an outdoor occupation or

recreational interest.

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Clinical features • Acute pulmonary blastomycosis usually presents as a nonspecific

influenza-like illness, similar to that seen with histoplasmosis or coccidioidomycosis.

• Most otherwise healthy persons recover after 2–12 weeks of symptoms, but some return months later with infection of other sites. Other patients with acute blastomycosis fail to recover and develop chronic pulmonary disease or disseminated infection.

• The skin and bones are the most common sites of disseminated disease. The skin is involved in more than 70% of cases; the characteristic lesions are typically raised, with a well-demarcated edge. It is from these skin lesions that the diagnosis is most often made.

• Osteomyelitis occurs in about 30% of patients, with the spine, ribs and long bones being the most common sites of infection. Arthritis occurs in about 10% of patients. Meningitis is rare, except in immunocompromised individuals.

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Laboratory diagnosis • Direct microscopy of pus, scrapings from skin lesions, or sputum

usually shows thick-walled yeast cells 5–15 μm in diameter that

characteristically produce buds on a broad base; the buds remain

attached until they are almost the size of the parent cell, often forming

chains of three or four cells. In biopsy material the yeasts are best seen

in stained sections.

• B. dermatitidis will grow in culture on Sabouraud agar (or blood agar)

without cycloheximide, to which the fungus is sensitive. The mycelial

phase develops slowly at 25–30°C and cultures must be retained for 6

weeks before discarding.

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• Test-tube slopes rather than Petri dishes are used for culture.

Identification is usually confirmed by subculture at 37°C to

convert it to the yeast phase.

• The most useful serological test is the immunodiffusion test using the

A antigen of B. dermatitidis. However, a negative result does not rule

out the diagnosis because the sensitivity ranges from 30% for

localized infections to 90% for cases of disseminated blastomycosis.

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Treatment

• Intravenous amphotericin B is used to treat all forms of blastomycosis

and is the drug of choice in serious life-threatening infection and the

drug of choice for rapidly progressive blastomycosis.

• Itraconazole follow-on therapy is given once the patient improves.

• Itraconazole or Ketoconazole for less severe cases that does not

involve the central nervous system.

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PARACOCCIDIOIDOMYCOSIS

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• The endemic region extends from

Mexico to Argentina, but the disease

is seen most frequently in Brazil,

Colombia and Venezuela.

• P. brasiliensis has been isolated from

soil, understanding of its precise

environmental reservoir remains

limited.

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PARACOCCIDIOIDOMYCOSIS

• This is a chronic granulomatous infection caused by the dimorphic

fungus Paracoccidioides brasiliensis that may involve the lungs,

mucosa, skin and lymphatic system. The disease may be fatal if

untreated.

• P. brasiliensis grows in the mycelial phase in culture at 25–30°C and in

the yeast phase in tissue or at 37°C on brain–heart infusion or blood

agar.

• The mould colonies are slow growing with a variable colonial

morphology, although most are white and velvety to floccose in texture

with a pale brown reverse.

• Spore production is usually sparse and best seen in 4–6-week-old

cultures.

• Asexual conidia may be produced but are not characteristic, and

identification depends on conversion from the mycelial to the yeast

phase.

• The yeast phase consists of oval or globose cells 2–30 μm in diameter,

with small buds attached by a narrow neck encircling the parent cell.

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Epidemiology

• Infection is usually acquired by inhalation; the incubation period is unknown.

• More than 90% of cases of symptomatic disease occur in men, most of whom

have agricultural occupations; oestrogen-mediated inhibition of the mould to

yeast transformation could help to account for this.

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Microscopical appearance of Paracoccidioides brasiliensis yeast

cells in sputum, showing multipolar budding.

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Paracoccidioides brasiliensis, yeast form

Multiple budding in the yeast form.

P. brasiliensis mycelial phase

in culture at 25–30°C

Colony appearance of Paracoccidioides brasiliensis on mycobiotic agar at

26◦C for 20 days

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Clinical features

• The lungs are the usual initial site of P. brasiliensis infection, but the organism

then spreads through the lymphatics to the regional lymph nodes.

• In most cases the primary infection is asymptomatic.

• Children and adolescents sometimes present with an acute disseminated form of

infection in which superficial and/or visceral lymph node enlargement is the major

manifestation. This presentation is also seen in immunocompromised patients. It

has a poor prognosis.

• In adults, paracoccidioidomycosis usually presents as an ulcerative

granulomatous infection of the oral and nasal mucosa and adjacent skin.

• In 80% of cases the disease involves the lungs. In some, the liver and spleen,

intestines, adrenals, bones and joints, and central nervous system are also

involved. The disease is slowly progressive, and may take months or even years

to become established.

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Laboratory diagnosis

• Microscopy of sputum or pus, crusts and biopsies from granulomatous

lesions usually reveals numerous yeast cells showing the characteristic

multipolar budding, which is diagnostic.

• In culture the mycelial and yeast phases both develop slowly and

cultures must be retained for 6 weeks before discarding.

• The mould phase can be isolated on Sabouraud agar supplemented

with yeast extract at 25–30°C, but colonies may take 2–4 weeks to

appear.

• Serological tests are useful for diagnosis and for monitoring the

response to therapy.

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Treatment

• The choice of therapy depends on the site of infection and

its severity.

• Oral itraconazole is the drug of choice, althoug

amphotericin B remains useful for severe or refractory

infections.

• Oral ketoconazole is almost as effective, but less well

tolerated than itraconazole.

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