Insect bite hypersensitivity (IBH) in horses has many common names – sweet itch, summer itch, Queensland itch and summer eczema. Each implies the main symptom, pruritus (itchy skin), in horses. Unfortunately, insect bite hypersensitivity is a common dermatological ailment in horses, especially those living near rivers and swamps. Although some studies suggest that bloodsucking insects like mosquitos are the cause of the allergic reaction, the main culprit is thought to be the Culicoides midge (Biting midge or No-See-Um gnat). The bite and saliva from the female Culicoides midge causes a Type-1 hypersensitivity which is an allergic reaction caused by exposure to a specific type of antigen. The allergic reaction causes inflammation in the affected areas causing itchy skin and hair loss commonly found along the chest, shoulders, mane, tail and midline of the abdomen.
Although a number of treatment options exist, prevention and insect control is the best strategy. Research has shown that the inflammation response to one bite can last up to one hour. A swarm of gnats can deliver up to 3,000 bites within an hour, and recovery from that kind of exposure can take three to six weeks. Researchers are working a vaccination to prevent horses from experiencing the allergic reaction caused by IBH; however, until the vaccine becomes available commercially, combining the tips below will help manage and treat IBH.
Reduce exposure to the Culicoides midge by disrupting its habits.
Use insecticides with 2% permethrin
Reduce itching with any of multiple options available to manage pruritus.
Control immune response
Treating and managing horses with insect bite hypersensitivity requires combining multiple therapies. Current treatments are unsuccessful when horses are overexposed to insects and other environmental allergens. Thus, success is dictated by early prevention and the owner’s commitment to management practices that reduce exposure and treat the symptoms. Research has shown that IBH is an inherited trait; therefore, animals affected by the condition should not be selected for breeding purposes.
Ginel, P.J., Hernandez, E., Lucena, R., Blanco, B., Novales, M., & E. Mozos. 2014. Allergen-specific immunotherapy in horses with insect bite hypersensitivity: a double-blind, randomized, placebo-controlled study. Vet Dermatol. 2014 Feb; 25(1):29-e10.
O’Neill, W.O., McKee, S., & A.F. Clarke. 2002. Flaxseed (Linum usitatissimum) supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity. Canadian Journal of Veterinary Research 2002; 66:272-277.
Jonsdottir, S., Hamza, E., Janda, J., Rhyner, C., Meinke, A., Marti, E., Svansson, V., & S. Torsteinsdottir. 2014. Developing a preventative immunization approach against insect bite hypersensitivity using recombinant allergens: A pilot study. Veterinary Immunology and Immunopathology. 166(2015) 8-21.
Wilson, A.D. 2014. Immune responses to ectoparasites of horses, with focus on insect bite hypersensitivity. Parasite Immunology, 2014, 36, 560-572.