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11/10/2015
1
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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