(described by Boedijn in 1933)
Description and Natural Habitats
Curvularia 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 [1219, 1295, 1806, 2144].
The genus Curvularia contains several species, including Curvularia brachyspora, Curvularia clavata, Curvularia geniculata, Curvularia lunata, Curvularia pallescens, Curvularia senegalensis, and Curvularia verruculosa. Curvularia lunata is the most prevalent cause of disease in humans and animals.
See the summary of synonyms and teleomorph-anamorph relations for Curvularia spp.
Pathogenicity and Clinical Significance
Curvularia spp. are among the causative agents of phaeohyphomycosis. Wound infections, mycetoma, onychomycosis, keratitis, allergic sinusitis, cerebral abscess, cerebritis, pneumonia, allergic bronchopulmonary disease, endocarditis, dialysis-associated peritonitis, and disseminated infections may develop due to Curvularia spp. Curvularia lunata is the most commonly encountered species. Importantly, the infections may develop in patients with intact immune system. However, similar to several other fungal genera, Curvularia has recently emerged also as an opportunistic pathogen that infects immunocompromised hosts [62, 66, 580, 642, 726, 913, 1262, 1285, 1429, 1475, 1927, 2042, 2252, 2270, 2297, 2468].
Curvularia 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 [531, 1295, 2144, 2202].
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 [531, 1295, 2144, 2202].
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.
See our histopathology page.
Curvularia is distinguished from Bipolaris and Drechslera by its conidial septa lying from one side wall to the other (not distoseptate). Also, unlike that of Bipolaris, conidium of Curvularia is usually curved, has an enlarged, darker central cell, thinner cell wall, and narrower septations between the cells [1295, 2144].
No special precautions other than general laboratory precautions are required.
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 [786, 913, 1491]. Caspofungin also appeared active in vitro against Curvularia lunata .
For MICs of various antifungal drugs for Curvularia, see our N/A(L):susceptibility database.
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 [462, 1262, 2270, 2297].