Scientists in South Korea have described a rapid method for diagnosing dermatophytosis.
Dermatophytosis, (“ringworm”) is an infection caused by fungi that attack the skin and associated keratinised structures such as hair and nails.
Fungal culture is the “gold standard” for identification of the species of dermatophyte involved, based on the colony characteristics and microscopic appearance. It is accurate but time consuming. Samples may have to be cultured for up to three weeks before the organism can be identified.
It’s not necessary to know the species of dermatophyte before starting treatment, Indeed, to prevent the spread of infection, treatment is usually started pending the results of laboratory investigations.
However there are occasions when it may be useful to know the identity of the dermatophyte involved, as it may help to identify the source of the outbreak. For example Trichophyton mentagrophytes can be found in soil and carried by rodents.
Researchers at the Colleges of Veterinary Medicine at Seoul National University and Konkuk University compared a rapid molecular method for diagnosing dermatophyte infection with conventional fungal culture.
Under the direction of Dr Cheol Yong Hwang, of the Department of Veterinary Internal Medicine at the Seoul National University College of Veterinary Medicine, the researchers examined samples taken from horses with suspected ringworm housed in Korean Racehorse Authority stables.
They collected hair samples from lesions on affected horses and from unaffected (control) horses and examined them by both PCR analysis and standard fungal culture. The PCR examination of the fungal DNA looked at the chitin synthase 1 (CHS-1) gene, which has specific characteristics in dermatophytes.
DNA analysis confirmed that of 57 suspected ringworm cases, 38 were indeed dermatophyte infections. PCR analysis of the CHS-1 gene of the fungal DNA produced fragments approximately 450bp in size - characteristic of dermatophyte fungi. These 38 samples also gave positive results on fungal culture.
Rapid confirmation of dermatophyte infection allowed the researchers to treat the affected cases with topical antifungal baths (ketoconazole twice weekly for 4 weeks.) This prevented any further spread of the infection.
Three of the positive samples were chosen at random for further testing, using gene sequencing. The results of this investigation confirmed that the dermatophyte involved was Trichophyton mentagrophytes.
The other 19 samples were negative both on PCR and standard culture fungal culture, as were all control samples.
The researchers conclude that the PCR assay is superior to traditional fungal culture for detecting fungal infection, “ in terms of sensitivity, specificity and particularly rapidity.”
For more details see:
A rapid molecular method for diagnosing epidemic dermatophytosis in a racehorse facility.
Chung T.H, Park G.B, Lim C.Y, Park H.M., Choi G.C, Youn H.Y, Chae J.S, and Hwang C.Y.
Equine Veterinary Journal (2010) 42, 73-78.