Dermatophytosis (Ringworm)

The typical lesion is a round, well-demarcated patch of hair loss with scale and crust that spreads outward. In cattle, grey-white, thick, asbestos-like crusts appear mainly on the head, neck and around the eyes, sometimes the rump or the whole body; when crusts are lifted a hairless, reddened area remains. Pruritus and restlessness may reduce feed intake. In dogs and cats, multifocal hair loss, redness, papules, pustules, scaling and crusts occur, often on the face, legs or tail, and prolonged inflammation can leave permanent hair loss. Lesions vary with fungal species, host and body site.

Dermatophytosis (ringworm) is a superficial fungal infection of keratinised tissue (skin, hair and nails or claws) caused by dermatophytes of the genera Microsporum, Trichophyton and Epidermophyton. Infective spores (arthroconidia) attach to keratin within hours, germinate and invade the stratum corneum, often through small wounds or damaged skin. The fungi secrete keratin-digesting and protein-digesting enzymes, including serine proteases, so they can live on keratin and damage host proteins; hairs are invaded from the outside (ectothrix). Cell wall components are recognised by innate immune receptors, triggering inflammatory cytokines that produce the redness, swelling and hair loss of a lesion. Outcome depends on fungal species, spore dose and host immunity; stress-related cortisol and weakened skin barriers, for example with zinc deficiency, favour infection.

The disease occurs worldwide and is one of the commonest zoonoses, and the zoonosis most often caught by veterinary staff in UK and Australian surveys. Trichophyton verrucosum causes most cattle ringworm, while Microsporum canis causes over 90% of cases in cats and is the leading cause in dogs; cats can carry it without signs. Spread is by direct contact and by spores on bedding, equipment and fomites, which can keep a herd infected for years. Young animals are most susceptible. In the region, 74% of samples from farm animals in Beheira, Egypt were positive (sheep 78%, buffaloes 76%, cattle 72%, horses 68%); 55.8% of 760 Egyptian calves had lesions, with risk raised by overcrowding, poor ventilation, beef systems, crossbreeding, parasites and newly bought animals; 11.5% of female camels sampled in central Saudi Arabia were affected; and herd prevalence in Irbid, Jordan cattle ranged from 10% to 100%.

Skin (stratum corneum, epidermis), hair and hair follicles, nails and claws

Avoid overcrowding, keep good ventilation and hygiene, isolate or check newly bought animals, control parasites, decontaminate housing and equipment, and wash hands after handling animals to limit spread to people.

Not fatal. Infection can resolve on its own, a common approach in cattle, and topical antifungal treatment of calves achieved clinical and mycological cure within 14-28 days in one trial. Spores in the environment can sustain herd infection for years.