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PARASITIC SKIN CONDITIONS LICE Horses are commonly infected especially during late winter and early spring with both sucking and biting lice. Animals in poor condition which are kept together in large numbers and are not groomed regularly often have heavy burdens.LIFE CYCLE Adult lice lay eggs which are attached to hairs. The nymph which hatches from the egg resembles the adult and matures through three larval stages the whole cycle taking place on the horse over a period of two to three weeks. CLINICAL SIGNS Lice occur particularly in the mane and tail-head areas but may spread anywhere in the body. In most cases there is little or no hair loss with only a moderate increase in skin scales. Loss of hair occurs in severe cases resulting in Irregularly shaped bare areas with ill-defined borders and some reddening of non-pigmented skin. Superficial abrasions may be caused by rubbing. The parasites make the skin itchy and the horse may rub against objects and nibble and lick at the skin. Extremely heavy infections of sucking lice may cause anaemia. EPIDEMIOLOGY Lice are host specific and do not live for more than a few days off the horse. Transmission is by direct contact or via grooming equipment, harness or bedding. TREATMENT Synthetic pyrethroid sprays (cypermethrin or permethrin) can be used. Selenium sulphide shampoo has been shown to be effective in a controlled clinical study. However, spray (noise) and shampoo (soaking) therapies have some logistical/expense problems for treatment of animals with full, winter haircoat. CHORIOPTIC MANGE (leg mange, itchy heel) Infection with non-burrowing mites. The prevalence of infection has been reduced with the fall in the number of heavy horses as it was common in breeds with heavy feather. Chorioptic mange tends to be more common in the winter. LIFE CYCLE Eggs are laid on the skin and hatch in 1 to 5 days. The subsequent larval and two nymphal stages do not penetrate below the skin surface and the life cycle is completed in 9 to 10 days. CLINICAL SIGNS Irritation caused by this parasite makes the horse stamp its feet and rub its lower limbs together. Lesions are mainly confined to the lower hind limbs but sometimes are present on all four legs and may extend upwards to appear occasionally on the body. The appearance of the lesions is often mild. Hair around the fetlock and pastern becomes broken and matted with dried exudate and in the upper limbs the skin may become bare, dry and visibly scaly EPIDEMIOLOGY Transmission is by direct or indirect contact. TREATMENT Synthetic pyrethroid sprays or washes, ivermectin orally, selenium sulphide shampoo, or 'Frontline' spray. Treatment should be combined with clipping and topical disinfection. HARVEST MITE INFECTION Infection with larvae of the harvest mite is not common in the West of Scotland but is common in the East and in some parts of England. The larvae come off the herbage and live for a few days on an animal causing minor irritation and itching of the horse *s heels without marked skin changes.The red or orange mite may be just visible with the naked eye. Horse limbs and faces may be dusted with insecticide once weekly in the autumn to prevent infection as this is the only time of year the condition occurs. WARBLES Warble flies rarely lay their eggs on the horse but larvae may migrate and reach the back and sometimes occur on unusual sites. Diagnosis is made on the appearance of the typical hemispherical lesion about 2 cm in diameter which may or may not have a central orifice. Lesions may be treated by incision of the lesion to remove the warble or local application of a recognised warble fly dressing. STABLE FLIES Stable flies in large numbers can attack horses, the bites being painful and bleeding easily. Multiple wheals and papules can develop, evolving into crusts on the back, chest, neck and legs. Lesions may represent arthropod hypersensitivity or may be caused by irritating and toxic components of saliva. DIAGNOSIS Diagnosis is by physical examination, and indicated by improvement of lesions if horses are stabled during the day when the flies feed. TREATMENT Treatment depends on frequent application of pyrethrin fly repellents and good stable hygiene - removing soiled bedding and manure from the stable and surrounding areas removes the breeding areas.BLACK FLIES Black flies are daytime feeders, attacking the sparsely haired areas of horses resulting in itchy, crusted papules and hair loss. Lesions are seen in the lower jaw and pectoral areas, lower body wall and inguinal areas, and also in the ears. DIAGNOSIS Diagnosis is again by physical examination and is indicated by response to daytime stabling. TREATMENT Treatment involves daytime stabling, frequent insecticide and repellent application. HORN FLIES Horn flies cause the syndrome of focal ventral midline dermatitis in horses. This is a seasonal irritation, characterised by one to many foci of hair loss, inflammation and depigmentation, scaling, crusting and excoriation centred around the umbilical area. TREATMENT Treatment is clipping and cleansing with mild antiseptic and application of antibiotic/corticosteroid cream to reduce inflammation. Fly repellents in a gel or ointment base provide a physical and chemical barrier against further bites. HORSE AND DEER FLIES Horse flies and deer flies inflict painful bites which can result in large wheels. Control is difficult owing to the robust nature of the flies. Heavy and frequent application of pyrethrins with repellents may give some relief. As the files require water for breeding and egg deposition, drainage of breeding grounds or moving horses from fly breeding areas, may be helpful |
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