Recognizing Trichophyton indotineae

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

• 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

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.

• Center for Medical Mycology of the University Hospitals Cleveland Medical Center (Cleveland, OH, USA)
  Contact: mag3@case.edu, lal11@case.edu, and ake27@case.edu

• Fungus Testing Laboratory, UT Health San Antonio (San Antonio, TX, USA)
  Contact: wiederholdn@uthscsa.edu

• Wadsworth Mycology Laboratory, New York State Department of Health (Albany, NY, USA)
  Contact: mycology@health.ny.gov

For onychodystrophy PCR testing with terbinafine resistance:

• BakoDx (Alpharetta, GA, USA)
  Contact form: https://bakodx.com/contact-us/

  • Note: testing may not be available in New York state

Additional resources