Infectious Disease and Microbiology - Bipolaris Species

Basics

Bipolaris species are darkly pigmented, filamentous fungi that can cause a spectrum of infections ranging from localized corneal and subcutaneous disease to invasive pulmonary, cerebral, and disseminated infections.

Important species include:

• Bipolaris australiensis

• Bipolaris hawaiiensis

• Bipolaris spicifera

Both immunocompetent and immunocompromised individuals can develop infection.

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Microbiologic Characteristics

Bipolaris species are dematiaceous fungi, meaning that melanin produces dark pigmentation within their fungal structures.

They are filamentous molds.

In culture, they typically:

• Grow relatively rapidly

• Produce cottony colonies

• Develop gray to black pigmentation

• Form hyphae at approximately 30°C

Within infected tissue, they may appear as:

• Yeast-like forms

• Pseudohyphae

• Septate pigmented hyphae

Infection caused by these pigmented fungi falls within the spectrum of phaeohyphomycosis.

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Epidemiology

Bipolaris organisms are environmental fungi commonly found in:

• Soil

• Plants

• Decaying vegetation

Humans may acquire infection through:

Traumatic inoculation

Penetrating injuries can introduce fungal elements directly into the skin, subcutaneous tissues, or eye.

Another route is:

Inhalation of environmental conidia

This route is particularly relevant to sinus and pulmonary disease.

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Clinical Infections

Fungal Keratitis

Bipolaris can cause mycotic keratitis, particularly after traumatic inoculation of the cornea.

Possible manifestations include:

• Eye pain

• Redness

• Photophobia

• Excessive tearing

• Corneal infiltrates

• Reduced visual acuity

Trauma involving soil or plant material is an important clinical clue.

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Subcutaneous Infection

Traumatic implantation may produce localized infection of the skin and subcutaneous tissues.

Manifestations can include:

• Nodules

• Cysts

• Abscess-like lesions

• Slowly enlarging subcutaneous masses

These infections can occur even in otherwise healthy individuals.

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Paranasal Sinusitis

Bipolaris is particularly associated with fungal sinus disease.

It may cause sinusitis in patients with:

• Allergic rhinitis

• Nasal polyposis

• Chronic sinonasal inflammation

It is an important cause of allergic fungal rhinosinusitis.

Patients may develop:

• Nasal obstruction

• Chronic sinus pressure

• Nasal discharge

• Recurrent sinusitis

• Nasal polyps

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Pulmonary Infection

After inhalation, Bipolaris may occasionally produce pulmonary disease.

Pulmonary infection is more concerning in patients with impaired immunity and may manifest with:

• Fever

• Cough

• Dyspnea

• Pulmonary infiltrates or nodules

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Central Nervous System Infection

Rarely, Bipolaris can cause severe CNS disease, including:

Meningoencephalitis

Cerebral involvement may result from direct extension or hematogenous dissemination.

Possible manifestations include:

• Headache

• Fever

• Altered mental status

• Seizures

• Focal neurologic deficits

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Disseminated Infection

Immunocompromised patients are at greatest risk for invasive and disseminated disease.

The fungus may spread from a pulmonary or other primary site to multiple organs.

Disseminated infection is considerably more serious than localized cutaneous or corneal disease.

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Diagnosis

Diagnosis requires demonstration and identification of the fungus in clinical specimens.

Methods include:

• Direct microscopic examination

• Histopathologic examination

• Fungal culture

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Histopathology

The demonstration of pigmented septate hyphae within infected tissue is an important clue to infection by a dematiaceous fungus.

However, morphology alone may not reliably distinguish Bipolaris from other pigmented molds, so culture or molecular identification may be needed.

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Culture

Fungal culture allows species identification.

Typical colonies are:

• Rapidly growing

• Cottony

• Gray to black

The dark pigmentation reflects the dematiaceous nature of the organism.

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Treatment

Treatment depends heavily on the site and severity of infection.

Corneal Infection

For fungal keratitis, a traditional topical treatment is:

Topical natamycin

Urgent ophthalmologic management is important because progressive fungal keratitis can threaten vision.

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Subcutaneous Infection

Localized subcutaneous infection may require:

Surgical excision

combined with antifungal therapy.

Agents that have historically been used include:

• Itraconazole

• Amphotericin B

• Ketoconazole

• Flucytosine

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Systemic Infection

Severe systemic disease has traditionally been treated with:

Intravenous amphotericin B

Azole antifungals may also have activity, depending on the isolate and clinical syndrome.

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Additional Antifungal Options

Other options include:

• Itraconazole

• Voriconazole

Clinical experience varies according to the infection site and species, so invasive disease should generally be managed with infectious-disease expertise and susceptibility information when available.

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Surgical Management

Surgery is particularly important for accessible localized lesions.

Possible interventions include:

• Excision of subcutaneous lesions

• Debridement of infected tissue

• Surgical management of sinus disease

• Ophthalmologic procedures for severe ocular infection

Antifungal therapy and surgery are often complementary.

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High-Yield Clinical Patterns

Corneal Disease

Eye trauma involving plant or soil material

Progressive keratitis

→ Consider Bipolaris fungal keratitis

Sinus Disease

Allergic rhinitis

Nasal polyps

Chronic fungal sinusitis

→ Consider a dematiaceous fungus such as Bipolaris

Immunocompromised Patient

Pulmonary infection

Neurologic manifestations or multiple organ involvement

→ Consider invasive or disseminated fungal infection

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Exam Essentials

Organism:

→ Bipolaris species

Important species:

→ B. australiensis, B. hawaiiensis, B. spicifera

Type:

→ Dematiaceous filamentous fungus

Environmental reservoir:

→ Soil and plants

Transmission:

→ Traumatic inoculation or inhalation of conidia

Tissue morphology:

→ Pigmented septate hyphae

Culture:

→ Rapidly growing cottony gray-to-black colonies

Major infections:

→ Keratitis, subcutaneous infection, fungal sinusitis, pulmonary disease, meningoencephalitis, disseminated infection

Important sinus association:

→ Allergic rhinitis and nasal polyposis

Corneal treatment:

→ Topical natamycin

Localized disease:

→ Antifungal therapy + surgical excision when appropriate

Systemic disease:

→ Systemic antifungal therapy

Key clinical pearl: Bipolaris is a pigmented environmental mold that should be considered when fungal keratitis follows plant or soil trauma or when allergic fungal sinusitis occurs in a patient with nasal polyposis.