Ringworm, Biology

Ringworm

It is also known as dermatophytosis resulting in alopecia, scab formation and ring like lesions in the affected body parts.

Etiology: Zeophilic fungi known as dermatophytes are present in the soil and produce the disease in both man and animals. About 99% cases of ringworm in animals are caused by Microsporum and Trichophyton species, and 80% case of ringworm in human beings in rural areas is caused by animal pathogens.

Pathogenesis: Fungi are strictly aerobic so they can not grow in the centre of lesions or below crusts but remain active at the periphery and that is the reason, they produce circular lesions and are named as ringworm .

Clinical signs: In bovines, circular lesions of about 2.5 cm diameter are seen as grey white crusts. Surface below scabs remains moist initially but is dried up later on and removed easily leading to development of alopecia. The lesions are primarily noticed in head and neck region but may be seen throughout the body in calves. Itching is absent, if there is no secondary bacterial infection'.

In horses, superficial lesions develop initially on trunk and rump and then spread to neck, head and limbs. Circular lesions of about 2.5 cm diameter are seen. From these areas, hairs are detached leaving a shining surface. Sometimes deeper lesions may also be seen causing infection of hair follicles, focal inflammation and suppuration.

Irritation and itching may be present. In sheep, lesions are found on head which are discrete, circular and have patchy alopecia. White grey crusts are also seen and animals mostly recover in one month. In pigs also, the lesions develop in circular pattern and alopecia occur at the centre of lesion. The disease is more common in dogs of below one year age, particularly in short-haired breeds. Ringworm of nails and arid claws is also common. Stubs of broken hairs and scab formation are also noticed in the affected patchy areas, Vesicles and pustules may develop with secondary bacterial invasion in some dogs leading to erythema and complete hair loss.

Diagnosis: It is diagnosed by clinical symptoms and confirmed by isolation of causal organisms from periphery of the lesions. Examination of skin scrapings also help in its confirmation. The scrapings are heated in 10% KOH and then examined under microscope to visualize the spores and mycelium. Infection with microsporum can also be detected by using Woods's lamp. Culturing of swabs taken from affected areas will also help in identification of the causal fungi. Sometimes, similar lesions are seen in mange infestation also which can be differentiated by skin scraping examination

Treatment: The crusts should be removed by soft brush and then 20% sodium caprylate solution, 10% ammoniated mercury ointment or a combination of 0.25% each propionic and undecylenic acids may be applied 2-3 times daily for 4-5 days. For local application, solution containing boric acid (10 parts), tannic acid (5 parts) and petroleum liquid (8 parts) may be used. If large number of animals are affected, bureax complex (copper sulphate 1.812 kg, unsoaked lime 1.812 kg, and water 40 gallon) can be used as a wash or spray at weekly interval. Sabourauds formula consisting of carbolic acid (15 parts), tincture iodine (25 parts) and chloral hydrate (10 parts) may be applied locally once daily for 4 days. When nails and claws are affected, 2% formaline may be applied. Captan (1:400) was found effective when used @ 4-7 litre/animal/week.

As systemic therapy, 10% sodium iodide can  be injected intravenously @ l g/ 15 kg body weight two or three times in a week. Griseofulvin @ 5-7.5 mg/kg body weight once daily for 7 days by oral route can be given for early recovery.

Control: Isolation of infected cases and adoption of hygienic measures are useful in controlling the disease.

Posted Date: 9/19/2012 2:00:55 AM | Location : United States







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