9 Dermatophytosis in a Jack Russell terrier
Dermatophytosis is a fungal invasion of keratinized tissue of the stratum corneum, hair or claws by Trichophyton, Epidermophyton or Microsporum spp. In small animals, dermatophytosis is most frequently associated with infections caused by Trichophyton or Microsporum spp. Dermatophytosis results in variable alopecia, erythema, scaling, crusting and pruritus. This case report describes a case of pruritic dermatophytosis caused by infection with Trichophyton erinacei.
There are aspects of the history that might alert the clinician to the possibility of dermatophytosis. These would include: breed predispositions to dermatophytosis (see ‘Epidemiology’ section); a history of exposure to a zoophilic or geophilic source of infection, such as a terrier breed hunting hedgehogs; evidence of contagion in contact animals or lesions on the owner suggestive of zoonosis; and the onset of skin disease in an animal with no previous history of skin problems. If there is pruritus, the appearance of alopecia or scaling prior to the onset of pruritus would suggest that this was not an allergic aetiology. A poor response to glucocorticoids, antibacterial or antiparasitic therapy could also be suggestive of dermatophytosis.
The relevant aspects of the history were:
There was mild peripheral lymphadenopathy, but there were no other abnormalities on general physical examination.
Examination of the skin revealed extensive patches of relatively well-demarcated alopecia, erythema, hyperpigmentation, and crusting and scaling over the muzzle, periorbital skin, the left dorsal trunk, the lateral thighs and the forelimbs (Figs 9.1, 9.2 and 9.3).
Figure 9.1 Well-demarcated alopecia, hyperpigmentation, scaling and crusting over the face. The nasal planum is unaffected.
Figure 9.2 Well-demarcated patch of alopecia, erythema and hyperpigmentation over the left carpal area.
Figure 9.3 Patchy alopecia, multifocal post-inflammatory hyperpigmentation and erythema over the left hind limb.
Multifocal patches of apparently spreading alopecia are suggestive of a folliculitis. The three common causes of folliculitis are demodicosis, pyoderma and dermatophytosis. In this case, the signalment, history and clinical presentation were highly suggestive of dermatophytosis resulting from infection with a Trichophyton spp.
The list of possible differential diagnoses included:
In a case like this, hypothyroidism and hyperadrenocorticism, or another underlying immunosuppressive disease, might predispose it to the development of pyoderma, demodicosis or dermatophytosis.
Multiple deep skin scrapings should be performed in any case where demodicosis is suspected. In this case there were crusting lesions and cytology was also indicated to identify the presence or absence of bacterial infection.
The following diagnostic tests were performed: