Ringworm

Synonym: Dermatophytosis, Tinea infection

• It is highly contagious skin disease of animals and man caused by more than one species of fungus.
• Disease name arises by appearance of cutaneous fungal infection in which lesion appear as circular ring of inflammation.
• It arises mainly in keratinized tissues of skin, i.e. horny cell layer of epidermis, ear, nails, hoof, horns.

Etiology:

• Until recent nomenclature, dermatophytes were classified as Fungi imperfecti because only sexual stage of reproduction known.
• Dermatophytes now has been classified into three genera, i.e. Microsporum, Trichophyton, and Epidermophyton based on appearance of microconidia.
• Different species of dermatophytes which causes lesion in domestic animals may be categorized as follows:

Epidemiology:

• Disease is distributed globally in animal species and human.
• Dermatophytes have seasonal distribution and related to pet animals during summer months and related to high rainfall and humidity.
• Outbreaks has been noted in pet animals during summer months in close confinement with inadequate nutrition.
• Young animals are more susceptible to infection. Calves are much more susceptible than adult cows.
• There is an increased risk of outbreaks during building work, with a much higher number of spores being released into the air.
• The incubation period of the disease is generally considered to be approximately one week although four weeks has been suggested as the period in some outbreaks.
• The overall incidence of ringworm based on evidence of hide damage in a number of European countries appears to be around 10% of cattle.
• Calves kept indoors or exposed to foggy weather with little or no sunlight have an increased incidence.
• Factors that affects susceptibility of animal to infection includes age, crowding together, poor nutrition, concurrent disease, use of immunosuppressive drugs, etc.

Transmission:

• Infection spreads to healthy animals through direct contact with infected animals.
• Infection may also spread through indirect contact with fomites such as harness, grooming utensils, beddings, coverings, etc.
• Infection may also spread through animal attendant/handler by their hands.
• Air borne infection is also possible.
• Spores of fungus can survive in infected hairs for more than 2 years outside the host.

Pathogenesis:

Clinical Findings:

Cattle and buffalo:

• Affected area of the skin becomes erythematous and hairs over the areas fall, thus giving picture of alopecia.
• Lesion are discrete and almost circular.
• Borders of lesion are raised having thick greyish crusts.
• Initially the surface under crust remains moist but later on they detach and pytiriasis develop.
• Lesion are mostly located on the head, around the eyes, neck, ears, and dewlap.

Sheep and goat:

• Lesion are usually seen on the head, neck, shoulder, chest, and back.
• Lesion appear as discrete, circular, alopecic patches covered with crust.

Pig:

• Lesion appear as erythematous, circular, and slightly raised patches.
• There is production of reddish-brown scales or crusts on the skin.
• Alopecia may not develop making it difficult to diagnose.
• Lesion are mostly noted on back and sides of body.

Horse:

• Lesion are superficial in nature and occurs as urticarial eruption with patches of alopecia.
• Ulcerative nodules are noted sometimes.
• Lesion produce irritation and itching.
• Lesion are most commonly seen on axillary or girth areas and spread generally over the trunk, neck, head and limbs.
• Desquamated areas may assume diffused moth-eaten appearance accompanied with alopecia.

Dog:

• In dog, lesion is usually located on face, extremities and lower abdomen.
• Lesion appear as small pink macules spreading in peripheral direction.
• Advanced lesion is circumscribed, discrete, confluent and covered with greyish scales which are attached to the skin.
• Secondary bacteria or mite may invade the lesion.
• In some cases, dog presents bee-hive appearance on the skin.

Cat:

• Lesion are found on the ears, face and extremities.
• Patches of alopecia with less erythema or crusty patches are most common exhibited lesion.
• Circular erythematous patches of atypical papular crust or vesicular dermatitis with or without alopecia are seen.
• Otitis externa, folliculitis without mass alopecia may also be seen.

Diagnosis:

• Based on characteristic lesion
• Microscopic examination of skin scrappings, nail, hair with 10% KOH. Hyphal fragments and spores may be noted.
• Isolation of organism through culture on SDA
• Examination of skin or affected parts with Wood’s Light method. Characteristic yellow-green color indicates presence of fungus.
• Skin test: Fungal antigen 0.1 mL can be given intracutaneously. The reaction can be noted after 24-48 hours

Differential Diagnosis:

• Mycotic dermatitis:
  • It involves inflammation of deeper layer of skin
  • Blood vessels and lymphatics are also involved.
• Tinea vesicular dermatomycosis in goat:
  • Lesion are circular, discrete, slightly thickened, and scaly at edge but not painful.
  • Darker coloration of skin

Treatment:

• Two types of drugs can be used; local and systematic drugs.
• Tolnaftate 1% solution can be used with Griesofulvin for quick result.
• Iodochlorhydroxyquin: Used to treat localized dermatophyte infection complicated by bacteria.
• Salicyclic acid 2-10%, Benzoic acid 2-6% can be used both as ointment and alcoholic solution.
• Haloproquin 1% cream can be used for 2-3 weeks.
• Phenol 4.5% have been found to have antifungal property.
• Miconazole 2% as topical cream or solution.
• Cotrimazole 1% as cream or solution can be used.
• Systemic antifungal agent such as Griesofulvin @ 10-16 mg/kg, in calf, 100mg/kg, b.wt. in horse for 20 days.
• Thiabendazole @ 2-5.5 mg/kg, b.wt. as systemic antifungal drugs.
• Ketoconazole @10mg/kg, b.wt. orally
• Antifungal shampoos containing 0.5% chlorhexidine, 2% miconazole or ketoconazole may be used.

Control Measures:

• Infected animals should be identified and isolated. They should be brought under treatment with drugs dependent upon nature of lesion.
• Utensils, grooming articles, feeding trough, etc. should be properly cleaned and treated as the fungal spores can resist desiccation and disinfection.
• Animal handlers should wash their hands properly before handling the non-infected ones.
• Wooden doors, windows, chain, rope used by the animal should be treated with 5% phenol or 2% formaldehyde or 1% caustic soda.
• Supplementation of vitamin A helps improve immunity
• Russian vaccine LTF 130 has been found to be useful against T. verrucosum infection in cattle at dose level of 5 ml at 10 days interval for 2 occasions. Calves can be vaccinated against ringworm with this vaccine at 1 months of age.