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A clinical condition caused by fungal infection of the skin in humans¹; but all domestic animals are susceptible.³ Dermatophytosis can be found in dogs (most often puppies), cats, cattle, sheep (common in show lambs), goats, horses, swine, rodents, rabbits (most often in young , newly weaned animals), and birds. The condition is caused by fungi of several different species and not by parasitic worms. In pets, the fungus responsible for the disease survives in skin and on the outer surface of hairs. They grow best in warm and humid environments and are, therefore, more common in tropical and subtropical regions.
Transmission: The fungus takes advantage of skin belonging to those with reduced immune capacity; keep in mind that skin must be abraded to become infected.² A carrier of ringworm is one that is infected but not showing lesions or one that is simply carrying the fungus on its fur in the same way an inanimate object might have fungal spores on its surface. Both types of “carriers” must be identified as they are both capable of spreading the infection. Most dermatophytes are readily transmitted to other susceptible host by contact and contamination of the environment. Fluorescence can appear on the fur within 7 days of exposure and clinical signs within 2 to 4 weeks. In humans, the incubation period is 1 to 2 weeks. Under most circumstances, dermatophytes grow only in keratinized tissue, and advancing infection stops on reaching living cells or inflamed tissue.³ Transmission between host usually occurs by direct contact with a symptomatic or asymptomatic host, or direct or airborne contact with its hairs or skin scales. Signs & Symptoms (Animals):
In animals, ringworm frequently looks like a dry, grey, scaly patch but can also mimic any other skin lesion and have any appearance.² Ringworm in pets may often be asymptomatic, resulting in a carrier condition which either infects other pets, or shows disease only when the companion animal develops an immunosuppressive condition. Circular bare patches on the skin suggest the diagnosis but no lesion is truly specific to the fungus.¹ Signs & Symptoms (Humans):
In humans, the clinical signs may vary depending on the region affected. The skin lesions are usually characterized by inflammation that is most severe at the edges, with erythema, scaling and occasionally blister formation. Central clearing is sometimes seen; this results in the formation of a classic “ringworm” lesion. In humans, dermatophytosis are referred to as “tinea” infections, and are named with reference to the area of the body involved; however, infections can spread to other areas.
Diagnosis: Dermatophytosis is diagnosed by fungal culture, examination with a Wood’s lamp, and direct microscopic examination of hair or skin scale. Fungal culture is the most accurate means of diagnosis.³ In humans, the diagnosis is similar to animals.
Treatment: Infected pets generally require oral medication which may be supplemented with topical treatment. Very localized lesions might get away with topical treatment only.² The ringworm fungus can remain infective in the environment up to 18 months, maybe longer. There have been several studies that showed that this fungal infection should eventually resolve on its own; typically, this takes 4 months.² Humans are usually treated with systemic or nonprescription antifungals; however, prescription drugs may be required if the fungus infects the hairs and recrudescence occurs. Topical lotions and drugs or shampoos are sometimes used to decrease shedding fungi and spores.
Prevention: To prevent transmission, infected animals should be isolated until the infection has resolved. The premises should be cleaned (vacuumed) and disinfected to help prevent infections to other animals and humans. Control of the disease in animals can prevent some cases of dermatophytosis in humans. Gloves and protective clothing should be used during contact with infected animals.