The dermatology unit offers a comprehensive referral service for all equine skin disorders. There is considerable experience in the diagnosis and treatment of allergic, immune mediated, parasitic and infectious conditions.
Patients receive individually tailored treatment programmes and as much long term follow-up as is appropriate to each case.
The unit has fruitful collaboration with colleagues in other disciplines when cases benefit from a multidiscipline approach.
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Sweet Itch Season
Culicoides hypersensitivity, also known as sweet itch, summer itch, Queensland itch or insect bite hypersensitivity, is common in horses and occurs in all part of the world where horses and Culicoides coexist. A breed predisposition is documented for the Icelandic horse, but also Shire horses, Fresian horses and Shetland ponies seem to be overrepresented. Affected individuals should ideally be removed from breeding programmes.
The main offending allergens are likely salivary allergens, shared by different species of Culicoides. More than 10 protein antigens, with the ability to bind IgE, are present in the insects’ salivary glands. In Icelandic horses, early induction of tolerance might be an important protecting factor for the disease.
Clinical signs are initially seasonal but may become perennial in chronic disease. Pruritus, papules, crusts and exudation normally involve the mane and tail. Lesions on the ventrum are possible, as there are species of Culicoides with predilection for this site. Horses traumatize affected areas, with consequent excoriations, alopecia, lichenification and secondary infections. Severely affected horses may develop a rat tail. The legs and intermandibular space are often involved. Horses may show irritability, restlessness and weight loss. Pruritus is worse in the early evening and early morning along with major midge activity. Some horses have concurrent atopy and/or food hypersensitivity, which complicates the diagnostic work-up and therapeutic management.
Differential diagnosis includes ectoparasitic infestations (lice, chorioptic and psoroptic mange), fly bites, Oxyuris infestations, onchocercal dermatitis, besnoitiosis, dermatophilosis, dermatophytosis, equine atopy, contact dermatitis, mane and tail follicular dystrophy.
Diagnosis is based on history, clinical signs with characteristic lesion distribution, seasonality and the exclusion other differentials. Several studies have been performed to develop a reliable intradermal test, but consistent results have not been obtained. In a recent study it was demonstrated that intradermal testing using Culicoides extracts relevant to the locality may be useful to support the clinical diagnosis. ELISA tests have also been validated, but sensitivity and specificity can vary depending on the local species of Culicoides involved.
The AHT's dermatology team are able to offer expert advice to referring vets on chronic cases of sweet itch, and work with referred cases on treatment and management plans to ensure the affected horse receives the correct aftercare.