Dermatophytes are fungi that can infect the skin, hair, and nails of humans and animals. There are three main genera: Microsporum, Trichophyton, and Epidermophyton. They grow slowly in culture and produce macroconidia or arthrospores. Microsporum species commonly cause ringworm infections in various animal hosts like horses, cattle, pigs, and chickens. Trichophyton species are also important animal pathogens and can infect multiple host species. Laboratory identification involves examining fungal culture morphology and microscopic characteristics of spores. Dermatophytes are an important cause of ringworm infections in veterinary medicine.

1. Dermatophytes
▪ Members of the phylum Ascomycota
▪ Affinity for keratinized structures; colonize and invade
skin, hair and nails
▪ Grow slowly on specially formulated laboratory media, e.g
Sabouraud dextrose agar; some require additional growth
factors
▪ Aerobic, tolerate cyclohexamide in media
▪ Colonies often pigmented
▪ Macroconidia formed in cultures
▪ Arthrospores, shed from infected animals, remain infective
for many months
▪ Cause characteristic circular skin lesions termed ringworm

2. Grouping of Dermatophytes
Based on host preference or habitat
▪ Zoophilic
▪ Anthropophilic
▪ Geophilic

3. Features of Dermatophyte Genera
Microsporum Tricohphyton Epidermophyton
Macroconidia Usually present Variable; often absent Present
Walls Thick Thin Thick
Surface Rough Smooth Smooth
Shape Spindle, cigar Club (slender) Club (broad)
Microconidia Variable; often
absent
Usual Absent
Sexual form Nannizia Arthroderma None known

4. Main zoophilic and geophilic dermatophytes
species responsible for ringworm in animals
Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.

5. Virulence factors possessed by Trichophyton
▪ Endoprotease (Subtilisins, Fungalysins)
▪ Exoproteases (Serine proteases, Leucine
aminopeptidases)
▪ Kinase
▪ Mannan
▪ Sulphite
▪ LysM

6. Virulence factors possessed by Microsporum
▪ Endoprotease (Subtilisins, Fungalysins)
▪ Pseudokinase (inactive kinase)
▪ Exoproteases
▪ Sulphite
▪ LysM along with polysaccharide deacetylases (type I)
▪ Polycyclic aromatic prenyltransferases (pcPTases)

7. Important Dermatophyte Infections in Animals
Host Agent Nature of Lesions
Horse T. equinum Dry, scaly usually noninflammatory (unless secondarily infected)
M. gypseum Often suppurative under alopecic thickened areas
M. equinum Not more than mildly inflammatory, resembling T. equinum lesions
Cattle T. verrucosum Painless, thick, white, ‘asbestos’ plaques, local alopecia
Swine M. nanum Tannish, crusty, spreading centrifugally on trunk; painless, margins
slightly inflamed. No hair loss.
Dog M. canis Typically noninflammatory, scaly, alopecic patches, occasional
kerion
T. mentagrophytes Often spreading, extensively scaling to inflammatory lesions,
secondary suppuration
M. gypseum As in T. mentagrophytes
Cat M. canis Often subclinical in adults. Generally noninflammatory, except in
young kittens, may become generalized in debilitated kittens.
Occasional mycetoma (Percisan cats).
T. mentagrophytes As in dogs
Chicken M. gallinae Generally affects unfeathered portions. Whitish chalky scaling on
comb and wattles, noninflammatory.
T. simii Superficially similar to M. gallinae but often inflammatory and even
necrotizing. A poultry problem only in India.

8. Importance
Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.

9. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.

10. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.

11. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Dermatophytosis in cats and dogs
M. canis infection in a kitten with lesions on the bridge of the nose,
the ear margins and the digits

12. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Kerion due to M. canis in a dog
Dermatophytosis in cats and dogs

13. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Numerous suppurative lesions due to T. mentagrophytes in a
hunting dog.
Dermatophytosis in cats and dogs

14. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Facial dermatophytosis due to M. persicolor in a hunting
dog.
Dermatophytosis in cats and dogs

15. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Total alopecia in an extensive dermatophytosis due to
M. canis in a Yorkshire Terrier.
Dermatophytosis in cats and dogs

16. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Chronic and extensive dermatophytosis due to a mixed M.
canis and T. mentagrophytes infection in a dog
Dermatophytosis in cats and dogs

17. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Dermatophytosis in horses
Ringworm due to M. gypseum in a horse
living on pasture

18. T. equinum lesions in a horse
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter
Dermatophytosis in horses

19. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Dermatophytosis in cattle
Cattle ringworm due to T. verrucosum with typical
periocular lesions

20. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Dermatophytosis in sheep
Ringworm in a sheep.

21. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.
Dermatophytosis in pigs
Dermatophytosis due to T. mentagrophytes
in a pig.

22. Different species of Trichophyton associated
with hair invasion
Ectothrix invasion Endothrix
invasion
Noninvasion
T. verrucosum T. schoenleinii T. rubrum
T. equinum T. violaceum T. simii
T. mentagrophytes T. tonsurans T. concentricum

23. ▪ Hairs should be plucked from the lesions.
▪ Scab material should be obtained from the edge of the
lesion.
▪ Scrapings and clipping from claws should be taken
from as near the base as possible.
▪ Where the specimens tend to be very contaminated by
bacteria and saprophytic fungi – wiping the lesions with
70% alcohol
Specimens
Laboratory Diagnosis

24. Surface (ectothrix) arthrospores on a hair
shaft following clearance with 10% KOH

25. Chermette R, Ferreiro L, Guillot J (2008) Dermatophytoses in animals. Mycopathologia 166: 385–405.

26. T. verrucosum: infected bovine hair with arthrospores

27. Morphological features of the macroconidia of some
Microsporum species

28. Morphological features of the macroconidia of
Trichophyton mentagrophytes and the chlamydospores
of T. verrucosum

29. Microscopic differentiation of the dermatophyte
genera affecting animals
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

30. Species Hosts Colonial Appearance Microscopic Appearance
Microsporum
canis (var.
canis)
Cats, dogs,
important
cause of
ringworm in
humans
Growth rapid. Surface white
and silky at centre with bright
yellowvperiphery. Reverse
side bright yellow or orange
Usually abundant
macroconidia. They are
spindle-shaped and
mature spores end in a distinct
knob. Cells 6–15. Few
microconidia
M. canis var.
distortum
Dogs Growth fairly rapid. Surface
white tovtan and reverse
white or yellowish tan. Colony
is velvety to fluffy with a
tendency to form radial
grooves
Usually abundant
macroconidia that are distorted
in shape,
thick-walled and multicellular.
Numerous microconidia
M. canis (syn.
M. equinum)
Horses Slow growth. Surface white
and velvety to finely powdery.
Reverse salmon or buff
Macroconidia rare, resemble
shortened M. canis
macroconidia
M. gypseum Horses,
dogs,
rodents
Fairly rapid growth. Colony is
flat, powdery with a fringed
border. Obverse is buff to
cinnamon-brown and reverse
pale yellow to tan or
occasionally red. Odour
similar to a mouse colony
Abundant macroconidia.
Boat-shaped with rounded
ends and thick, rough walls.
Cells 4–6
Dermatophytes of Veterinary Significance

31. Species Hosts Colonial Appearance Microscopic Appearance
M. nanum Pigs Colony is flat, white and
cottony at first, later granular
and buff coloured
Abundant macroconidia,
pear-shaped with spiny walls.
Cells 1–3.
M. gallinae Chickens,
turkeys
Rapid growth. Surface white
to pinkish, velvety and folded.
Reverse strawberry-pink,
diffusible pigment
Abundant macroconidia,
fusiform
with blunt spatulate tips. Walls
smooth and thick. Cells 2–10.
Trichophyton
equinum
Horses Fairly rapid growth. Colony
initially flat, white and fluffy
but later velvety with central
folding. Cream to tan in
colour, reverse is yellow to
reddish-brown
Macroconidia are rare. Slightly
club-shaped, smooth, thin-
walled with 3–5 cells.
Abundant microconidia.
Chlamydospores are abundant
in old cultures
Trichophyton
equinum var.
autotrophicum
Horses Colony at first white with a
raised centre, later white to
buff with folded centre.
Reverse is yellow becoming
dark rose-red
Macroconidia not reported
Dermatophytes of Veterinary Significance – cont’d

32. Species Hosts Colonial Appearance Microscopic
Appearance
T. mentagrophytes
var. mentagrophytes
Rodents,
dogs,
horses
and many
other
species
Rapid growth. Two colony
forms: 1. Granular, obverse
cream, reverse buff-tan to
dark-brown; 2. Downy, white
and woolly with older colonies
becoming cream-tan, reverse
varies from white through
yellow to reddish-brown
Macroconidia
cigarshaped,
thin-walled. Cells 3–7.
Abundant
microconidia in grape-
like clusters
T. simii Monkeys,
poultry,
dogs
Rapid growth. Finely granular
colony with diffuse margin,
white to pale or rose-buff.
Reverse white and later
reddish-brown
Abundant macroconidia,
cylindrical to fusiform in
shape. Cells 3–10.
T. verrucosum Cattle Very slow-growing. Small,
white,
velvety, heaped and folded
colony. Obverse white or
whitish-grey and occasionally
yellow-ochre, reverse is white
Macroconidia very rare
but characteristic chains
of chlamydospores
Dermatophytes of Veterinary Significance – cont’d

33. M. canis on SDA: surface white and silky at
centre with bright yellow periphery (obverse)
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

34. M. canis on SDA: bright yellow or orange (reverse)
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

35. M. gypseum: flat, powdery with a fringed
border (obverse)
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

36. M. gypseum: pale yellow to tan colour
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

37. M. nanum: colony is flat and cottony at
first, later granular and buff-colored.
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

38. M. nanum: orange, becoming reddish
brown (reverse)
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

39. T. equinum: colony initially flat, white and
fluffy but later velvety with central folding
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

40. T. equinum: yellow to reddish brown (reverse)
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

41. T. mentagrophytes: granular type colony
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

42. T. mentagrophytes: dark brown to buff tan (reverse)
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

43. T. verrucosum: small, white, velvety,
heaped and folded colony
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

44. T. verrucosum (reverse side)
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

45. Microsporum canis: spindle shaped macroconidia
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

46. M. gypseum: boat-shaped macoconidia
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

47. Trichophyton mentagrophytes: numerous
microconidia and cigar-shaped macroconidium
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

48. M. nanum: pear-shaped macroconidia
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter

49. Hair perforation test
▪ Collect hairs from a young child with fair hair.
▪ Layer the sterile hairs on a 3-5-day-old subculture of
the dermatophyte under test and incubate at 25°C.
▪ Examine the hairs daily from seventh day of
incubation onwards by mounting a few hairs in
lactophenol cotton blue and examining them
microscopically, using the low and high-dry
objectives.

50. In vitro hair perforation test

51. Trichophyton mentagrophytes: illustrating in-vitro hair
penetration by this dermatophyte seen as wedge-shaped,
dark-blue areas
Clinical Veterinary Microbiology by P. J. Quinn, M. E. Carter, B. Markey, G. R. Carter