Dermato phytoses, Biology

Dermato phytoses

Dermatophytosis (ringworm) is a cosmopolitan, superficial and highly contagious disease of man, animals and birds. The infection is caused by fungi of three genera, viz. Trichophyton, Microsporum and Epidermatophyton, collectively termed as dermatophytes. The fungi most commonly invade the keratinized layers of the skin and sometimes hair and nail. There appears to be great overlapping in the clinical symptoms produced by these dermatophytes. Microsporum does not attack nails whereas Epidermatophyton never invades the hair. The disease is of considerable economic and public health significance. The affected animals cause great damage to hides, skin, wool and hair besides causing decrease in milk production and loss of condition. The diseased animals, particularly pets and cattle, serve as an important reservoir of infection for man. About 80 % of ringworm cases in human are directly derived from animals. The disease may be restricted to a single animal or it may occur as outbreaks involving a large number of animals. Young animals are more susceptible and the disease is marked with seasonal periodicity, the incidence of the disease is high in winter. The clinical signs depend on many factors which include age of animal, sex, species, general condition, nutrition, overcrowding as well as virulence and dose of the fungus. Infection is contracted directly from sick animals or indirectly from inanimate objects such as buckets, grooming kits, blankets, beddings, harnesses and walls of the sheds. The animals which carry the fungal spores without any lesions may  also act as important source of infection to others.

The affected animal shows small, circular, discrete, raised patches. The surface is covered with scales and greyish-white crusts. The hair in lesion become dull, lustreless, soft, brittle and are easily pulled out forming hairless scabbed area. The patches of baldness may merge and reach the size of palm. The lesions occur most frequently on head, face and neck region; however, abdomen, brisket, shoulder, limb, flank, rump and other parts of the body are also involved. Lesions vary in size and may be less than a centimetre to extensive in area. All the determatophytes give rise to mild to severe types of inflammatory reactions. Sometimes bacterial invasion may complicate the lesion, and microabscesses develop in the intraenidermal and intradermal layers of skin. The infection is zoonotic in nature and man acquires the infection from the diseased animals. Since man is an unusual host for animal dermatophyte, a marked and severe local inflammatory reaction may occur which is self-limiting; and subsides in due course of time.

Diagnosis: Clinical picture is usually suggestive of ringworm. The skin scraping should be examined under microscope after mounting in 10% potassium hydroxide or sodium hydroxide for branched, septate hyphae and arthrospores. In the skin all the 3 genera of dermatophytes form arthrospores and branching hyphae, and thus cannot be distinguished from one another. For this purpose, isolation of the causative fungus on Sabouraud‘s medium is necessary. The lactophenol mount of the culture is required for studying the morphology of the fungus. Spindle or boat-shaped conidia are the characteristics of Microsporum. Trichophyton shows cylindrical micro-conidia. Peat shaped conidia are observed in Epidermatophyton. Ultraviolet Wood‘s light is not much used in the diagnosis of dermatophytosis, though it may be helpful in recognizing M. canis and M. audouinii infection by exhibiting fluorescence.

Treatment and prevention:
Since the disease is contagious, it is advisable to isolate the affected animals from the healthy animals and looked after separately. In large animals vigorous brushing of the coat to remove brittle and infected hair and crusts is necessary before the application of drug. The individual lesions should be thoroughly painted daily with tincture of iodine, 3% salicylic acid ointment, 6 % benzoic acid, copper sulphate and zinc oxide solution (5% drug). Hair should be clipped in pets and then treated with proprietary medicines such as Zole ointment, Clomazole ointment, Jagit ointment, Tineaserm liquid, Himax, Betadine and Multifungin. Oral therapy with Griseofulvin at 10-20 mg/kg body weight for 21 days is usually recommended in severe case in man and pet animals. As the condition occurs most commonly in young calves kept under unhygienic conditions, the use of sulphur sublimate and calcium lactate at 2 g each daily in feed for 15-21 days may help in minimizing the prevalence of ringworm in young animals. Besides, potassium iodide at 4 g daily orally for 4-5 days may be useful in quick recovery. The contaminated building, equipment and bedding should be disinfected by spraying copper sulphate solution or 5% lime sulphur suspension. This will diminish the reservoir of infection. The skin crust which is full of fungal hyphae and spores should be properly disposed off to check the spread of infection from diseased animal to other susceptible animals or human beings. Keeping  in view the public health significance of ringworm infection, the animal attendant, pet owner, zoo-worker and laboratory personnel should take full precautions while dealing with affected animals or their skin scrapings. Antifungal drugs such as Grisovin are used with moderate success.

Posted Date: 9/17/2012 8:14:42 AM | Location : United States

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