Pseudallescheriasis and Scedosporium infection

Description:

A spectrum of disease similar in terms of variety and severity to those caused by Aspergillus. The vast majority of infections are mycetomas, the remainder include infections of the eye, ear, central nervous system, internal organs and more commonly the lungs. Infections result from either inhalation of air-borne conidia or by the traumatic implantation of fungal elements due to a penetrating injury. The etiological agents are Pseudallescheria boydii (anamorph Scedosporium apiospermum), Scedosporium aurantiacum and Scedosporium prolificans.

Clinical manifestations:

1. Pseudallescheria boydii and Scedosporium aurantiacum infections:

Non-invasive colonization of the external ear and pulmonary colonization in patients with poorly draining bronchi or paranasal sinuses and "fungus ball" formation in pre-formed cavities are similar to those seen in Aspergillus.

Invasive infections in normal patients are usually caused by traumatic implantation. Mycetoma, where the fungus exists in tissue as resistant microcolonies or grains is the most common infection in the normal patient. This is followed by penetrating joint injuries, especially to the knee, resulting in arthritis and osteomyelitis. Other manifestations include mycotic keratitis and non-mycetoma like cutaneous and subcutaneous infections.

Invasive infections have also been reported in patients receiving treatment with corticosteroids and immunosuppressive therapy for organ transplantation, leukemia, lymphoma, systemic lupus erythematous or Crohn's disease. Infections include invasive sinusitis, pneumonia, arthritis with osteomyelitis, cutaneous and subcutaneous granulomata, meningitis, brain abscesses, endophthalmitis, and disseminated systemic disease.

MIC data for Scedosporium apiospermum (Australian Scedosporium Study)

MIC data for Scedosporium aurantiacum (Australian Scedosporium Study)

2. Scedosporium prolificans infections:

The spectrum of clinical manifestations are similar to that described above for P. boydii. Disseminated disease has been reported in immunosuppressed patients especially those with prolonged neutropenia and post-transplantation therapy. Colonization of the external ear, paranasal sinuses and lung, including "fungus ball" have been reported. Cases of onychomycosis and mycotic keratitis have also been documented. However, localized invasive infections, especially septic arthritis and osteomyelitis following penetrating injuries to joints, are now an emerging clinical problem, accounting for 80% of the reported cases. Culture identification is important, because this fungus is often resistant to antifungal therapy and treatment may require surgical intervention.

MIC data for Scedosporium prolificans (Australian Scedosporium Study)

Laboratory diagnosis:

1. Clinical material: Sputum, bronchial washings and tracheal aspirates from patients with pulmonary disease and tissue biopsies from patients with subcutaneous and disseminated disease.

2. Direct Microscopy: (a) Sputum, washings and aspirates make wet mounts in either 10% KOH & Parker ink or Calcofluor and/or Gram stained smears; (b) Tissue sections should be stained with H&E, GMS and PAS digest. Note hyphal elements of Pseudallescheria boydii and Scedosporium prolificans are indistinguishable from those of Aspergillus hyphae and may be missed in H&E stained sections. Examine specimens for branched, septate hyphae.

Interpretation: The presence of branching septate hyphae in any specimen, from a patient with supporting clinical symptoms should be considered significant. Biopsy and evidence of tissue invasion is of particular importance. Remember culture is necessary for a specific identification of the causative agent.

3. Culture: Colonies are fast growing and are greyish-white, to olive-grey to black with a suede-like to downy surface texture.

Interpretation: P. boydii, S. aurantiacum and S. prolificans are common soil fungi, therefore a positive culture from a non-sterile specimen, such as sputum or skin, needs to be supported by direct microscopic evidence in order to be considered significant. A positive culture from a biopsy or aspirated material from a sterile site should be considered significant. Culture identification is the only reliable means of distinguishing these fungi from Aspergillus species.

4. Serology: As in cases of aspergillosis immunodiffusion tests have become valuable in the diagnosis of pseudallescheriasis. However, at present reagents are not commercially available and antigenic extracts have to be made in the laboratory.

5. Identification: Culture characteristics and microscopic morphology are important, especially conidial morphology, the arrangement of conidia on the conidiogenous cell and the morphology of the conidiogenous cell, in this case an annellide.

Causative agents:

Scedosporium apiospermum, Scedosporiun aurantiacum, Scedosporium prolificans.

Treatment Guidelines

Further reading:

Ajello L and R.J. Hay. 1997. Medical Mycology Vol 4 Topley & Wilson's Microbiology and Infectious Infections. 9th Edition, Arnold London.

Gilgado, F., J. Cano, J. Gene and J. Guarro. 2005. Molecular phylogeny of the Pseudallescheria boydii species complex: proposal of two new species.   J. Clin. Microbiol. 43:4930-4942.

Kwon-Chung KJ and JE Bennett 1992. Medical Mycology Lea & Febiger.

Richardson MD and DW Warnock. 1993. Fungal Infection: Diagnosis and Management. Blackwell Scientific Publications, London.

Rippon JW. 1988. Medical Mycology WB Saunders Co.

Warnock DW and MD Richardson. 1991. Fungal infection in the compromised patient. 2nd edition. John Wiley & Sons.