Trichophyton concentricum

Growth and morphology

Trichophyton concentricum produce dense, slow-growing folded colonies which are mostly white to cream colored on Sabouraud's dextrose agar and their hyphae are normally branched, irregular and septate with antler tips resembling T.schoenleinii. The production of conidia is unusual, however when present, microconidia and macroconidia are smooth walled with a diameter of approximately 4 microns and 50 μm respectively. Due to its resemblance to macroconidia, hyphae are sometimes falsely identified as macroconidia. These fungi are also considered to be osmotolerant because of their ability to grow small colonies on 5% NaCl media. Hair perforation assays are generally negative with T. concentricum and growth is poor at 37 °C. While T. concentricum is considered to be independent of external vitamin sources, growth is more robust with thiamine supplementation. This characteristic feature is commonly used to distinguish between T. concentricum and T. schoeleinii. Overall, the natural habitat and growth of T. concentricum is not well understood and further studies are required.

Reproduction

Trichophyton concentricum reproduces sexually via its ascospores which are produced internally in vacuoles called asci (sing. ascus), found in pouches known as ascomata (sing. ascoma). The asexual form of T. concentricum is composed of irregularly arranged filaments with chlamydoconidia and microaleurioconidia.

Pathology and treatment

Scrapings from lesions can be stained with 10% potassium hydroxide for visualization under microscope. The medium Sabouraud's dextrose agar is commonly used for colony growth and is treated with antibiotics to prevent bacterial contamination. Colonies growth is usually observed in 1–2 weeks at 25 °C. Identification using polymerase chain reaction is also possible, this provides an accurate rapid diagnosis.

Treatment of tinea imbricata is usually with griseofulvin combined with a topical imidazole agent which is administered until cured. Treatment with griseofulvin or terbinafine has also been successful when combined with a keratinolytic agent, such as a topical cream. Griseofulvin which is administered orally, serves to disrupt fungal mitosis, hence prevents the division and spread of fungal cells . Compared to griseofulvin, azole and allylamine agents have not been found to be as effective in treating tinea imbricata. However, griseofulvin has not shown to be effective as a prophylactic agent to prevent tinea imbricata. The eradication of T.concentricum is believed to be difficult due to high recurrence and presence in remote rural areas.

Epidemiology

Trichophyton concentricum is endemic to the Pacific Islands and southeast Asia, particularly in the indigenous hill tribe people. 9-18% of individuals in these regions are affected. Cases of T. concentricum infection among the South and Central American indigenous people has also been reported. Infections among Europeans are rare. The vast range of climates in the endemic regions has led to speculations about the existence of two strains: a thermotolerant strain which lives between 28 and 30 degrees Celsius and a thermo-sensitive strain which lives between 20 and 25 degrees Celsius. However, no evidence has been found to support this theory.

Tinea imbricata has been found in equal proportions in males and females and distributed equally among all age groups. The disease affects mostly individuals with particular genetic ancestry; and lack of proper hygienic conditions have been shown to increase risk of infection. Additionally, dietary conditions, hygiene, environment, immune considerations, and genetics are factors believed to play a role in susceptibility.

References

References

1. (July 2004). "Tinea imbricata or Tokelau.". International Journal of Dermatology.
2. (1982). "Medical mycology : the pathogenic fungi and the pathogenic actinomycetes". Saunders.
3. "Trichophyton concentricum".
4. (1983). "Immune responses of patients with tinea imbricata". British Journal of Dermatology.
5. "Dermatophytosis". University of Adelaide.
6. (July 2004). "Tinea imbricata or Tokelau". International Journal of Dermatology.
7. (1992). "Medical mycology". Lea & Febiger.
8. SERJEANTSON, S. (1977). "Autosomal Recessive Inheritance of Susceptibility to Tinea Imbricata". The Lancet.
9. (2012-05-01). "Identification of rare macroconidia-producing dermatophytic fungi by real-time PCR". Medical Mycology.
10. (2012). "Fundamental medical mycology". Wiley-Blackwell.
11. (April 1994). "A double-blind, randomized, stratified controlled study of the treatment of tinea imbricata with oral terbinafine or itraconazole". British Journal of Dermatology.
12. (1964). "Study of Prophylactic Action of Griseofulvin—Human Experimental Infection with Trichophyton Concentricum". Journal of Investigative Dermatology.