Infectious Disease and Microbiology – Pseudallescheria boydii

Overview

Pseudallescheria boydii is a filamentous fungus (mold) characterized by septate, hyaline hyphae. It has historically also been associated with the name Scedosporium apiospermum, although modern taxonomy distinguishes sexual and asexual forms within the Scedosporium/Pseudallescheria complex.

This environmental mold has a worldwide distribution and can cause both localized and invasive disease. Important manifestations include eumycetoma, pulmonary infection, brain abscess, osteomyelitis, sinusitis, ocular infection, endocarditis, fungal balls, and disseminated infection.

A particularly important clinical feature is that its invasive infections can closely resemble aspergillosis, but P. boydii/Scedosporium is characteristically poorly susceptible or resistant to amphotericin B.

Classification

Genus: Pseudallescheria

Species: Pseudallescheria boydii

Historical/related terminology:

Scedosporium apiospermum

Organism type: Filamentous fungus (mold)

Hyphae: Hyaline and septate

Microbiologic Characteristics

The characteristic morphology includes:

• Septate hyaline hyphae

• Filamentous mold growth

• Fungal aggregates or granules in mycetoma

• Hyaline septate hyphae in invasive hyalohyphomycosis

Because the hyphae may resemble those of Aspergillus, microbiologic identification is important.

High-Yield Microbiology Pattern

Hyaline mold

• ●

Septate hyphae

• ●

Aspergillus-like appearance

• ●

Poor amphotericin B activity

→ Think Pseudallescheria/Scedosporium

Incubation Period

The incubation period is:

Unknown

For mycetoma, infection is generally chronic and slowly progressive following environmental inoculation.

Epidemiology

P. boydii has a:

Worldwide distribution

The organism occurs environmentally in:

• Soil

• Polluted water

• Sewage-contaminated environments

• Organic material

Mycetoma is particularly common in:

Tropical and subtropical regions

Transmission

Localized infection may develop after:

Traumatic inoculation

of contaminated environmental material into:

Skin or subcutaneous tissue

This helps explain the frequent involvement of exposed areas such as:

Feet and hands

Mycetoma

One of the classic manifestations of P. boydii infection is:

MYCETOMA

Mycetoma is a chronic infection involving:

Skin + subcutaneous tissue

and may eventually extend into:

Bone

Classic Mycetoma Triad

The classic clinical triad is:

Tumefaction

• ●

Draining sinus tracts

• ●

Granules in the drainage

→ MYCETOMA

This is one of the most important exam patterns associated with the disease.

Tumefaction

Mycetoma produces a:

Slowly enlarging, tumor-like swelling

The lesion is usually chronic and may progress over a prolonged period.

Draining Sinus Tracts

As infection progresses, multiple:

Sinus tracts

may develop between the infected tissue and skin surface.

These tracts can discharge:

Pus containing characteristic granules

Granules

The granules contain aggregates of the causative organism.

In fungal mycetoma, microscopic examination may demonstrate:

Fungal hyphae within the granules

Recognition and culture of these structures can help identify the causative organism.

High-Yield Mycetoma Pattern

Tropical exposure

• ●

Chronic swelling of foot

• ●

Multiple draining sinuses

• ●

Granules in pus

→ Think MYCETOMA

Eumycetoma vs. Actinomycetoma

Mycetoma can be caused by either:

True fungi

or

Filamentous bacteria

Eumycetoma

Caused by:

Fungi

Examples include:

Pseudallescheria/Scedosporium

and other mycetoma-producing molds.

Actinomycetoma

Caused by filamentous bacteria such as:

Nocardia

and certain other aerobic actinomycetes.

Historically, Actinomyces has also appeared in discussions of mycetoma-like infections.

High-Yield Distinction

Eumycetoma

→ Fungal

Actinomycetoma

→ Bacterial

Both may produce:

Swelling + sinus tracts + granules

Sites of Mycetoma

The most characteristic sites are:

Feet

and

Hands

because these exposed areas are susceptible to traumatic environmental inoculation.

However, infection may occur on:

Any exposed body surface

Madura Foot

Mycetoma involving the foot is classically known as:

Madura foot

The clinical picture is:

Chronic foot swelling

• ●

Draining sinus tracts

• ●

Granules

Osteomyelitis

Chronic infection may extend from soft tissue into:

Underlying bone

resulting in:

Osteomyelitis

Bone involvement is an important complication of advanced mycetoma.

Hyalohyphomycosis

Outside the classic mycetoma syndrome, P. boydii can produce:

Hyalohyphomycosis

This refers to infection caused by molds that demonstrate:

Hyaline, septate hyphae in tissue

Aspergillus-Like Disease

An important diagnostic problem is that invasive P. boydii infection can resemble:

Aspergillus

in terms of:

• Clinical presentation

• Tissue appearance

• Septate hyphal morphology

Therefore:

Septate hyphae in tissue do not automatically mean Aspergillus.

Culture or other organism-specific identification is important.

High-Yield Diagnostic Trap

Septate hyaline hyphae

→ Do not automatically diagnose Aspergillus

If culture identifies:

Pseudallescheria/Scedosporium

the therapeutic implications are important because of differing antifungal susceptibility.

Pulmonary Infection

P. boydii may cause:

Pneumonia

particularly in susceptible patients.

Pulmonary disease can resemble:

Invasive pulmonary aspergillosis

and may occur in patients with underlying lung disease or impaired immunity.

Fungal Ball

The organism can colonize preexisting pulmonary cavities and form:

Fungal balls

This can closely resemble an:

Aspergilloma

High-Yield Pulmonary Pattern

Preexisting lung cavity

• ●

Fungal ball

• ●

Aspergillus-like septate hyphae

→ Consider Scedosporium/Pseudallescheria as well as Aspergillus

Brain Abscess

A particularly serious manifestation is:

Brain abscess

CNS disease can occur following dissemination or particular environmental exposures.

Neurologic manifestations depend on the location and extent of infection.

Near-Drowning Association

An especially important clinical association with Scedosporium apiospermum is:

Near-drowning in contaminated water

followed later by:

Central nervous system infection or brain abscess

This organism can be present in polluted water, making this exposure an important diagnostic clue.

High-Yield CNS Pattern

Near-drowning

• ●

Contaminated/polluted water exposure

• ●

Delayed brain abscess

→ Think Scedosporium apiospermum

Meningitis

The source also identifies:

Meningitis

as a possible manifestation.

CNS infection is serious and may be difficult to treat.

Eye Infections

Ocular manifestations may include:

• Keratitis

• Endophthalmitis

• Other invasive ocular infections

These may follow:

Trauma

or other direct inoculation events.

Sinusitis

P. boydii may cause:

Fungal sinusitis

The clinical and histopathologic appearance may resemble infection caused by other hyaline molds.

Endocarditis

Rarely, the organism may cause:

Endocarditis

This is a serious invasive manifestation and may require combined:

Antifungal therapy + surgical management

depending on the circumstances.

Disseminated Infection

In susceptible patients, P. boydii can cause:

Disseminated fungal infection

with involvement of multiple organs.

Risk is increased in patients with:

Significant immunosuppression

Diagnosis

Diagnosis is based on:

Culture

and

Identification of the organism in tissue biopsy specimens

For mycetoma, examination of:

Granules from draining sinus tracts

is particularly useful.

Examination of Granules

The granular material discharged from mycetoma lesions contains:

Aggregates of fungal elements

Microscopic examination can provide clues to the causative organism.

Culture is needed for more specific identification.

Histopathology

Tissue examination may demonstrate:

Septate hyaline hyphae

However, this appearance can resemble:

Aspergillus

Therefore, morphology alone may not reliably distinguish the two.

Culture

Culture is particularly important because:

Correct identification directly affects treatment

This is especially true when differentiating Scedosporium/Pseudallescheria from Aspergillus.

Treatment

The source emphasizes that treatment data are limited.

Historically, high-dose azoles such as:

• Itraconazole

• Miconazole

• Ketoconazole

were recommended.

For invasive Scedosporium apiospermum/Pseudallescheria boydii infection, voriconazole has become an especially important systemic antifungal option.

Amphotericin B Resistance

One of the most important treatment facts is:

AMPHOTERICIN B IS OFTEN INEFFECTIVE

against P. boydii/S. apiospermum.

This contrasts with many other serious invasive mold infections.

High-Yield Treatment Pattern

Aspergillus-like invasive mold infection

• ●

Septate hyaline hyphae

• ●

Poor response/resistance to amphotericin B

→ Think Scedosporium/Pseudallescheria

Surgical Management

Localized infection may require:

Surgical excision or debridement

This is particularly important for:

• Mycetoma

• Osteomyelitis

• Localized deep infection

• Abscesses

• Infected or necrotic tissue

Thus, management may require:

ANTIFUNGAL THERAPY

• ●

SURGICAL SOURCE CONTROL

Treatment of Mycetoma

Fungal mycetoma can be difficult to eradicate.

Management may require:

• Prolonged antifungal therapy

• Surgical debridement

• Excision of localized lesions

• Management of associated osteomyelitis

Extensive disease may be particularly challenging.

Pseudallescheria/Scedosporium vs. Aspergillus

Both can demonstrate:

Hyaline septate hyphae

and both may cause:

• Pneumonia

• Sinusitis

• CNS infection

• Fungal balls

• Disseminated disease

However:

Aspergillus

→ Classic acute-angle branching septate hyphae

→ Amphotericin B formulations can have activity against some species

Scedosporium apiospermum / Pseudallescheria boydii

→ Can closely mimic Aspergillus

→ Amphotericin B often has poor activity

→ Voriconazole is an important therapeutic agent

→ Notable association with CNS infection after near-drowning

Pseudallescheria vs. Mucorales

Pseudallescheria/Scedosporium

→ Septate, hyaline hyphae

Mucorales

→ Broad, ribbon-like, typically pauciseptate or aseptate hyphae

Thus, the hyphal morphology can help narrow the differential.

Pseudallescheria vs. Nocardia

Both may be associated with:

Mycetoma

However:

Pseudallescheria

→ Fungus

→ Hyaline septate hyphae

→ Eumycetoma

Nocardia

→ Filamentous bacterium

→ Gram-positive branching organism

→ Often weakly acid-fast

→ Actinomycetoma

Prevention

There is no specific vaccine.

General preventive measures include:

• Protecting feet and hands from penetrating environmental trauma

• Wearing footwear in endemic areas

• Cleaning contaminated wounds

• Appropriate management of traumatic injuries

• Avoiding unnecessary exposure of open wounds to contaminated soil or water

High-Yield Mycetoma Pattern

Tropical region

• ●

Chronic painless swelling of foot

• ●

Draining sinus tracts

• ●

Granules

→ Mycetoma

If caused by a hyaline mold such as Pseudallescheria:

→ Eumycetoma

High-Yield Invasive Pattern

Near-drowning in polluted water

• ●

Delayed CNS infection/brain abscess

• ●

Septate hyaline mold

→ Think Scedosporium apiospermum

Exam Essentials

Historical name: Pseudallescheria boydii

Related/currently used name: Scedosporium apiospermum complex

Type: Filamentous fungus (mold)

Hyphae: Hyaline and septate

Distribution: Worldwide

Mycetoma distribution: More common in tropical/subtropical regions

Classic localized disease: Eumycetoma

Classic mycetoma triad: Tumefaction + draining sinuses + granules

Classic site: Foot (Madura foot) and hands

Possible complication: Osteomyelitis

Other infections: Pneumonia, sinusitis, brain abscess, meningitis, ocular infection, endocarditis, fungal balls, and disseminated infection

Important exposure: Near-drowning → CNS infection/brain abscess

Histopathology: Septate hyaline hyphae

Major mimic: Aspergillus

Diagnosis: Culture + tissue biopsy, with examination of mycetoma granules when present

Major treatment clue: Amphotericin B often ineffective

Important systemic agent: Voriconazole

Source-listed azoles: High-dose itraconazole, miconazole, or ketoconazole

Source control: Surgical debridement/excision may be necessary

Key clinical pearl: Pseudallescheria boydii/Scedosporium apiospermum is a hyaline, septate mold that can cause eumycetoma or invasive disease closely resembling aspergillosis. Remember two particularly high-yield clues: chronic swelling with draining sinuses and granules indicates mycetoma, while delayed brain abscess after near-drowning in polluted water strongly suggests Scedosporium. Unlike many invasive molds, it often responds poorly to amphotericin B, making correct identification therapeutically important.