Culicoides Hypersensitivity

Also known as Sweet Itch

Description

Culicoides hypersensitivity, commonly referred to as 'Sweet itch' is an intensely pruritic dermatitis of horses caused by a hypersensitivity reaction to the saliva of biting Culicoides midges. The condition may be seasonally recurring or continuous depending on the climate

Pathogenesis

The condition is thought to occur due to both immediate (Type 1) and delayed (Type 4) hypersensitivity reactions to Culicoides salivary proteins. The proteins are injected during feeding and IgE antibodies are produced in repsonse by susceptible animals.

Clinical signs

The cardinal sign of Sweet itch is extreme, intense pruritus with characteristic distribution patterns. Commonly affected areas include the head, mane, tail, withers and ventral abdomen. Primary lesions are papules but self-excoration may lead to the characteristic lesions of sweet itch including alopecia, broken hairs, erosions, ulcers. In the chronic stages, lichenification is a common feature.

Diagnosis

Diagnosis is often based on the animal's history, seasonal clinical signs and the site and nature of the lesions. Other important differential diagnoses that should be ruled out include psoroptic and sarcoptic mange, other insect-related and dermatophilosis

Treatment

• Grossly:s
  • Papules, crusts, alopecia, excoriations, lichenification
• Microscopically:
  • Superficial and dep perivascular dermatitis
  • Many eosinophils
  • Epidermal hyperplasia
  • Hyperkeratosis
  • Dermal fibrosis
  • Possibly eosinophilic folliculitis, intraepidermal pustules and eosinophilic granulomas