Curvularia: Introduction, Morphology, Pathogenicity, Laboratory Diagnosis and Treatment
Introduction of Curvularia/Cochliobolus
Curvularia lunata is even being a fungal plant pathogen that can cause disease in humans and other animals. The anamorph of this fungus is Curvularia lunata, while Cochliobolus lunatus denotes the teleomorph or sexual state. They are, however, the same biological entity. C. lunata is the most commonly reported species in clinical cases of reported this infection. The genus Curvularia contains some 35 species which are mostly subtropical and tropical plant parasites; however, three ubiquitous species, C. lunata, C. pallescens, and C. geniculate have been recovered from human infections.
Scientific Classification of Curvularia
- Kingdom: Fungi
- Phylum: Ascomycota
- Class: Dothideomycetes
- Subclass: Pleosporomycetidae
- Order: Pleosporales
- Family: Pleosporaceae
- Genus: Curvularia
- Species: C. lunata
Morphology of Curvularia
Macroscopic features of Curvularia , colonies are fast-growing, suede-like to downy, brown to blackish. 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. 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 whereas in C. lunata include brown to black color, hairy, velvety, or woolly texture and loosely arranged and rapidly growing colonies on Sabouraud dextrose agar(SDA). Microscopically, there is great variety in the arrangement of the septate conidiophores, as they can be isolated or in groups, straight or bent, show simple or geniculate growth patterns, and varied in color ranging from pale to dark brown. Conidiophore length can reach 650 μm and are often 5-9 μm wide, with swollen bases ranging from 10-15 μm in diameter. Conidia develop at the tips and sides of the spores and have a smooth texture. C. lunata is differentiated from other Curvurlaria species by its 3 septa and 4 cells, with the first and last cells usually of a paler shade of brown than those in the middle. Conidia range from 9-15 μm in diameter and have a curved appearance.
Pathogenicity
Following are the diseases caused by Curvularia –
Phaeohyphomycoses
- Curvularia lunata is one of the main causative agents of Phaeohyphomycoses.
- Initial infection through breaks to the epidermal barrier or the inhalation of spores can lead to disseminated infections, which are often associated with a poor prognosis.
- C. lunata is an opportunistic pathogen, infecting immunocompromised patients and those on rigorous steroid drug regimens such as solid organ transplant recipients, advanced AIDS patients, and cancer patients.
- Dematiaceous fungi such as C. lunata can facilitate foreign body infections of heart valves, catheters, and pacemakers.
Allergy
Allergic fungal manifestations include asthma, rhinitis, sinusitis, and bronchopulmonary mycoses caused by a variety of etiological fungal agents including C. lunata. Allergic rhinitis, more commonly known as hay fever, is less frequently encountered in clinics compared to allergic fungal sinusitis.
Eye infection
Mycotic keratitis and conjunctivitis are more commonly reported in tropical climates. Environmental factors such as wind, temperature, rainfall, and humidity have been found to influence the ecology of filamentous fungi. In incompetent atopic individuals, 17% of those affected with allergic fungal sinusitis can develop orbital mycotic symptoms, where the fungus acts as an allergen causing allergic mucin. Pre-existing allergic fungal sinusitis, allergic conjunctivitis, and the use of soft contact lenses are risk factors for the development of opthalomycosis. Above mentioned three species also recovered from human infections like cases of subcutaneous, endocarditis, peritonitis and disseminated infections have also been reported in an immunosuppressed patient.
Risk group: The organism comes under risk group (RG)-1.
Laboratory diagnosis of Curvularia
Direct smear examination
Wet mount preparation
Culture
Colony characteristics
Velvety texture
Mold type growth
Pigmentation
Morphology
Lactophenol cotton blue (LPCB)
Other methods
Skin test
Serological test
Differential diagnosis of allergic bronchopulmonary mycosis is difficult, and it is often misdiagnosed as tuberculosis, pneumonia, bronchiectasis, lung abscess, or bronchial asthma. In this condition, following several serological tests can be performed to assess total IgE and allergen-specific IgE and IgG:
Enzyme-Linked Immuno-sorbent Assay (ELISA)
MAST,
HIA, and
CAP RAST.
Treatment of Curvularia
The anti fungal drugs available for treatment are-
- Amphotericin B
- Itraconazole
- Fluconazole
- Posaconazole
- Voriconazole.
But treatment is based on the site of infection and condition of the patient e.g.treatment for allergic fungal sinusitis includes a post-operative corticosteroid and aggressive anti-allergic inflammatory regimen including itraconazole or amphotericin B, while treatment for bronchopulmonary mycosis usually does not include surgery and similarly in eye infection, Typical therapy includes administration of natamycin and azole group such as itraconazole, fluconazole, posaconazole, and voriconazole.
Bibliography
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- Clinical Microbiology Procedure Handbook, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
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