Microsporum canis
February 1, 2003 (published)
Susan Little DVM, DABVP (Feline)

Winn Feline Foundation Progress Report
By Susan Little DVM, Diplomate ABVP (Feline)

February 2003

Determination of Strain Variability of Microsporum canis
Investigators: K.A. Moriello, D.J. DeBoer, L. Volk
School of Veterinary Medicine,
University of Wisconsin, Madison, WI

Funded 1997

A number of studies have examined the fungicidal activity of various disinfectants against Microsporum canis, the fungus that causes ringworm. These studies often use the isolated infected hair model, rather than actual cats infected with ringworm. Results from various researchers have not always agreed, and this may be due to differences in the strains of M. canis used in the studies.

This study was designed to test the hypothesis that different strains of M. canis may react differently to disinfectants. The researchers evaluated 5 different disinfectants (Virkon® S, chlorhexidine, lime sulfur, enilconazole, bleach) using eight different dilutions. Sterile water was used as a control solution. The disinfectants were tested for their efficacy against 10 different strains of M. canis.

Isolated infective spores of from each strain of M. canis were incubated with the various disinfectant concentrations and then placed onto fungal culture plates. A different culture plate was used for each combination of M. canis strain, disinfectant, and disinfectant dilution. Fungal cultures were examined seven and 10 days later.

It was found that there was no difference among the 10 different strains of M. canis. Of the disinfectants tested, chlorhexidine and Virkon® S (Antec International Ltd) were ineffective, even when used at four times the manufacturer's recommended strength. Lime sulfur (1:33 dilution), enilconazole (20 ?l/ml), and bleach (1:10 dilution) were effective when used at the recommended dilutions. Further, both lime sulfur and enilconazole were consistently effective even when used four times as dilute as the manufacturer recommends.

The researchers found that different strains of M. canis do not appear to vary in their sensitivity to disinfectants. Of the common disinfectants tested, bleach, lime sulfur and enilconazole were the most effective. Lime sulfur is available in a veterinary formulation called LymDyp® (DVM Pharmaceuticals). Bleach is commonly available for household use.

Enilconazole is not available in small animal formulations in the U.S. It is sold as an environmental spray for poultry operations as Clinafarm-EC® (Janssen Animal Health). In Canada, enilconazole is sold as a dip, which is licensed for use on horses and dogs under the brand name Imaverol® (Janssen Animal Health). Other formulations are available in Europe. Some studies have shown potential liver toxicities when enilconazole is used topically on cats, especially Persians, so this product should only be used under the supervision of a veterinarian.

For Further Reading:

  1. Moriello KA, DeBoer DJ, Volk L. (2002) Determination of strain variability of Microsporum canis to disinfectants. Proc American Academy/American College Veterinary Dermatology Annual Meeting, New Orleans, LA.
  2. Moriello KA, DeBoer DJ, Volk L. (2002) Determination of strain variability of Microsporum canis to disinfectants. Veterinary Dermatology 13(4): 211.