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Recognizing Trichophyton indotineae


Banner for Emerging dermatophytes
Reporting to health departments

Physicians who suspect antimicrobial-resistant dermatophytosis can also contact their state or local health departments for assistance. Public health officials who are concerned about potential cases or clusters of drug-resistant tinea infections can email fungaloutbreaks@cdc.gov for assistance with recommendations and testing.

Overview and epidemiology of Trichophyton indotineae

  • In the last decade, a recently emerged dermatophyte species, Trichophyton indotineae, has been causing major outbreaks of severe, difficult-to-treat, and frequently relapsing infections in South Asia among immunocompetent patients.1-2

  • T. indotineae often has genetic mutations that can make it resistant to antifungal drugs, including terbinafine, a common first-line oral therapy.3

  • The prevalence of T. indotineae is unknown due to lack of surveillance, but cases have been identified in 6 continents and in multiple U.S. states.3-7

  • T. indotineae was previously called Trichophyton mentagrophytes type VIII and may be referred to by this name in older studies.8

  • It has mostly been reported to spread person-to-person (e.g., through skin-to-skin contact or shared objects).2

  • Rare cases in animals have been documented, and it is possible that animals could serve as a reservoir.9,10

  • Potential sexual transmission among humans has also been reported.11

T. indotineae morphology and natural history

  • Images of patients showing signs of infection by Trichophyton indotineae
    Image courtesy of Ziyang Xu, MD, PhD and Avrom S. Caplan, MD, FAAD.
    Dermatophytosis caused by T. indotineae may be severe (covering large regions of the body) and difficult to treat.1

  • Lesions may be atypical. Multiple morphologies are reported, including erythematous, scaly concentric plaques (i.e., ring-on-ring appearance [“pseudoimbricata”]), papulosquamous, pustular, and steroid-modified tinea.4,12

  • Patients may report recent travel (e.g., within the prior 3 months) or contact with someone who has travelled to South Asia, where these infections have become widespread in certain regions.4 However, domestic cases in patients without a travel history have also been reported.4

  • Patients may report previous trials of topical or oral antifungal medications, including oral terbinafine, without response.4

  • Patients may report a history of using topical corticosteroid products for severe pruritus, which can make the infection worse.4

Diagnosing T. indotineae

  • Potassium hydroxide (KOH) preparation of skin scrapings is an important tool to confirm the diagnosis of dermatophytosis.12

  • It is important to note that culture-based testing used at most clinical laboratories cannot distinguish T. indotineae from T. mentagrophytes or T. interdigitale, two common species of dermatophyte.4

  • Identifying T. indotineae requires specialized testing (e.g., ITS genome sequencing) available only at select laboratories,4 listed below.

  • Laboratories that identify T. indotineae may also report minimal inhibitory concentration (MIC) values for particular antifungal medications. See Preventing and treating Trichophyton indotineae for more information.

  • Antifungal susceptibility testing may have limited benefit for individual patient care but is important for assessing population-level changes in susceptibility patterns to inform future treatment recommendations.12


Trichophyton mentagrophytes13
Under a magnification of 475X, this photomicrograph revealed some of the ultrastructural morphology exhibited by the dermatophytic fungal organism, Trichophyton mentagrophytes
Under a magnification of 475X, a photomicrograph reveals ultrastructural morphology exhibited by T. mentagrophytes, specifically, this dense cluster of microconidia, and their associated hyphae, which together, is referred to as an en grappe arrangement.


Testing laboratories

Below is a list of laboratories that perform testing to identify T. indotineae and other severe and antimicrobial-resistant dermatophytes. Clinicians can contact the laboratories for details on sample submissions.

For onychodystrophy PCR testing with terbinafine resistance:


References
  1. Verma SB, Panda S, Nenoff P, et al. The unprecedented epidemic-like scenario of dermatophytosis in India: I. Epidemiology, risk factors and clinical features. Indian J Dermatol Venereol Leprol. Mar-Apr 2021;87(2):154-175. doi:10.25259/IJDVL_301_20.

  2. Uhrlass S, Verma SB, Graser Y, et al. Trichophyton indotineae-An Emerging Pathogen Causing Recalcitrant Dermatophytoses in India and Worldwide-A Multidimensional Perspective. J Fungi (Basel). Jul 21 2022;8(7)doi:10.3390/jof8070757.

  3. Lockhart SR, Chowdhary A, Gold JAW. The rapid emergence of antifungal-resistant human-pathogenic fungi. Nat Rev Microbiol. Dec 2023;21(12):818-832. doi:10.1038/s41579-023-00960-9.

  4. Caplan AS. Notes from the field: first reported US cases of tinea caused by Trichophyton indotineae—New York City, December 2021–March 2023. MMWR Morbidity and Mortality Weekly Report. 2023;72.

  5. Canete-Gibas CF, Mele J, Patterson HP, et al. Terbinafine-Resistant Dermatophytes and the Presence of Trichophyton indotineae in North America. J Clin Microbiol. Aug 23 2023;61(8):e0056223. doi:10.1128/jcm.00562-23.

  6. Messina F, Santiso G, Romero M, Bonifaz A, Fernandez M, Marin E. First case report of tinea corporis caused by Trichophyton indotineae in Latin America. Med Mycol Case Rep. Sep 2023;41:48-51. doi:10.1016/j.mmcr.2023.08.004.

  7. Mosam A, Shuping L, Naicker S, et al. A case of antifungal-resistant ringworm infection in KwaZulu-Natal Province, South Africa, caused by Trichophyton indotineae. Accessed 6/21/2024, https://www.phbsa.ac.za/wp-content/uploads/2023/12/PHBSA-Ringworm-Article-2023.pdf.

  8. Kano R, Kimura U, Kakurai M, et al. Trichophyton indotineae sp. nov.: A New Highly Terbinafine-Resistant Anthropophilic Dermatophyte Species. Mycopathologia. Dec 2020;185(6):947-958. doi:10.1007/s11046-020-00455-8.

  9. Jabet A, Brun S, Normand AC, et al. Extensive Dermatophytosis Caused by Terbinafine-Resistant Trichophyton indotineae, France. Emerg Infect Dis. Jan 2022;28(1):229-233. doi:10.3201/eid2801.210883.

  10. Oladzad V, Nasrollahi Omran A, Haghani I, Nabili M, Seyedmousavi S, Hedayati MT. Multi-drug resistance Trichophyton indotineae in a stray dog. Res Vet Sci. Jan 2024;166:105105. doi:10.1016/j.rvsc.2023.105105.

  11. Spivack S, Gold JAW, Lockhart SR, et al. Potential Sexual Transmission of Antifungal-Resistant Trichophyton indotineae. Emerg Infect Dis. Apr 2024;30(4):807-809. doi:10.3201/eid3004.240115.

  12. Khurana A, Sharath S, Sardana K, Chowdhary A. Clinico-mycological and therapeutic updates on cutaneous dermatophytic infections in the era of Trichophyton indotineae. J Am Acad Dermatol. Apr 3 2024;doi:10.1016/j.jaad.2024.03.024.

  13. Trichophyton mentagrophytes. Public Health Image Library. Accessed 6/24/2024, https://phil.cdc.gov/Details.aspx?pid=22305.

Additional resources

Preventing and treating Trichophyton indotineae

See Academy information on prevention and treatment of T. indotineae.

Trichophyton mentagrophytes type VII

See Academy guidance on T. mentagrophytes type VII and other emerging dermatophytes.

Trichophyton rubrum resistant to terbinafine

See Academy information on T. rubrum resistant to terbinafine.

Emerging diseases registry

Report suspected cases of antifungal-resistant dermatophytosis, mpox, and COVID-19.

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