Queensland Itch

Description

Queensland Itch is the result of a hypersensitive reaction to allergens in the saliva of Culicoides midges, also known as "sand flies" or "no see'ms." The hypersensitive response leads to severe itching, causing horses to become distressed and rub and bite themselves intensely. Prolonged rubbing and biting results in hair loss and damage to the skin to such an extent that open sores develop which often become infected by bacteria.

Symptoms

• Intense itching
• Allergic reaction causing blisters at the site where the insects bite
• Open sores with crusting, scabbing, and scaling
• Lesions around ears and head
• Loss of patches of hair caused by rubbing and biting
• Skin thickening and loss of hair pigmentation
• Secondary infections

Causes

Queensland Itch is caused by hypersensitivity to protein molecules in the saliva of Culicoides midges. The hypersensitivity is the result of an antibody produced by the horse's immune system that binds to the allergens, causing production of histamines and cytokines that cause inflammation in the horse's skin.

Prevention

The best prevention for Queensland Itch is insect control and protecting the horse from being bitten. Barrier techniques that keep flies and midges from biting the animal include the use of rugs and fly masks. Screening stable doors and windows with fine screen will help exclude biting insects. Stabling the horse at the times of day, usually dawn and dusk, when midges are most active, can also be effective.

Midges tend to breed near water sources, such as ponds, bogs, and slow-moving water. Keeping horses away from these areas can be helpful since midges are not strong fliers.

Use of insecticides and repellents, especially permethrins and benzyl benzoate, applied either to the horse or the environment, can be helpful in minimizing bites.

Treatment

Once lesions or sores develop, few treatments are fully successful. Several companies are working to develop immunotherapy products. To date, the success rates are variable, but work is being done on developing a vaccine protocol that will reduce or modify the immune response in the horse. Antihistamines control symptoms to some degree.

Antibiotics are usually prescribed by the veterinarian when secondary infections are present.