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CURVULARIA Mould
The U.S. Government's
Occupational Safety and Health Administration [OSHA]
lists the
following as the health effects of curvularia mould:
Allergen, Irritant, Hypersensitivity pneumonitis, Dermatitis. |
Taxonomic Classifications
Kingdom:
Fungi
Phylum: Ascomycota
Class: Euascomycetes
Order: Pleosporales
Family: Pleosporaceae
Genus: Curvularia
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Toxic Mould
Species:
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brown hyphae and conidia septate hyphae mature conidia usually have 4 segments,
3rd segment from base (site of
attachment) becomes enlarged giving conidia a curved appearance
(Courtesy of
Veterinary Pathobiology) |
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Culture of Curvularia lunata |
conidia of Curvularia lunata |
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Colonies are fast growing, suede-like to downy, brown to blackish brown
with a black reverse. Conidia are pale brown, with three or more
transverse septa (phragmoconidia) and are formed apically through a pore
(poroconidia) in a sympodially elongating geniculate conidiophore
similar to Drechslera. Conidia are cylindrical or slightly
curved, with one of the central cells being larger and darker.
Germination is bipolar and some species may have a prominent hilum.
(Courtesy of
Mycology Online) |
Description and Habitats
Curvularia mould is a dematiaceous
filamentous fungus. Most species of Curvularia are facultative
pathogens of soil, plants, and cereals in tropical or subtropical areas,
while the remaining few are found in temperate zones. As well as being a
contaminant, Curvularia may cause infections in both humans and
animals.
Curvularia species
are commonly found as a parasites or saprobes (saprophytes) on graminaceous
hosts (= grasses and cereals). The conidia (= spores) are multicelled, pigmented
and often slightly curved. The end cells are often much paler than the
central cells. The conidia are borne in acropetal succession (= youngest at
the apex) through tiny pores in the conidiophore wall and are easily
dislodged.
Species Based on the
mycological information provided by Mycology Online, the genus
Curvularia contains some 35 species which are mostly subtropical and
tropical plant parasites. However, three ubiquitous species have been
recovered from human infections, principally from cases of mycotic keratitis;
C. lunata, C. pallescens and C. geniculata.
Health Effects Curvularia
is a dangerous
mould which can be a cause of human infection, including onychomycosis, keratitis,
sinusitis, mycetoma, pneumonia, endocarditis, cerebral abscess, and
disseminated infection.
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Cuvularia mould growing in a mould culture plate. Identifying
Filamentous Fungi by Guy St.-Germain & Richard Summerbell.
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Macroscopic Features
Curvularia
mould
produces rapidly growing, woolly colonies on potato dextrose agar at 25°C.
From the front, the color of the colony is white to pinkish gray initially
and turns to olive brown or black as the colony matures. From the reverse,
it is dark brown to black.
Microscopic
Features
Septate,
brown hyphae, brown conidiophores, and conidia are visualized. Conidiophores
are simple or branched and are bent at the points where the conidia
originate. This bending pattern is called sympodial geniculate growth. The
conidia (8-14 x 21-35 µm), which are also called the poroconidia, are
straight or pyriform, brown, multiseptate, and have dark basal protuberant
hila. The septa are transverse and divide each conidium into multiple cells.
The central cell is typically darker and enlarged compared to the end cells
in the conidium. The central septum may also appear darker than the others.
The swelling of the central cell usually gives the conidium a curved
appearance.
The number of the septa in the conidia,
the shape of the conidia (straight or curved), the color of the conidia
(dark vs pale brown), existence of dark median septum, and the prominence of
geniculate growth pattern are the major microscopic features that help in
differentiation of Curvularia spp. among each other. For instance,
the conidia of Curvularia lunata have 3 septa and 4 cells, while
those of Curvularia geniculata mostly have 4 septa and 5 cells
Laboratory Precautions
No special precautions other than general
laboratory precautions are required.
Susceptibility
Very few data are available
and there is as yet no standard method for in vitro susceptibility testing
of Curvularia spp. Notably, flucytosine
yielded very high MICs for Curvularia isolates tested. The MICs of fluconazole
were also quite high. In contrast, amphotericin
B, ketoconazole,
miconazole,
itraconazole,
and voriconazole
showed favorable activity and generated acceptably low MICs for most of the Curvularia
isolates tested. Caspofungin
also appeared active in vitro against Curvularia lunata
Treatment modalities for Curvularia
infections have not been standardized yet. Amphotericin B, itraconazole, and
terbinafine have so far been used to treat Curvularia infections.
However, the prognosis is usually poor, particularly for immunocompromised
patients. For treatment of allergic sinusitis, surgical treatment and
administration of steroids are usually required as well as antifungal
therapy. Surgery may be required in other infections as well, such as
keratitis and localized cutaneous infections.
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