Study on Insect Bite Hypersensitivity in Horses

Insect bite hypersensitivity (IBH), also known as "summer eczema" or "sweet itch," is a common condition in horses caused by bites from Culicoides midges. These bites cause intense itching, leading affected horses to scratch frantically, resulting in excoriated lesions. To better understand the effects of IBH on equine welfare, Swedish researchers studied the impact of this hypersensitivity on horse movement activity and behavior.

Study Background

The study included 30 horses—16 with IBH and 14 controls—in a prospective crossover and case-control study over two summers. Both IBH-affected and control horses were stabled in the same paddock, providing them with similar environmental experiences and exposure to Culicoides.

Inflammation and itching result from an allergic response (Type I hypersensitivity) to antigens in the saliva of biting midges. These midges preferentially feed along the mane, the base of the tail, in the ear pinnae, and along the intermandibular area and ventral midline. Affected horses will go to great lengths to relieve the itching, even to the point of significant self-trauma resulting in open and ulcerated wounds. This behavior can cause changes such as restlessness, depression, anxiety, nervousness, and potential weight loss due to the stress and discomfort.

Observations and Results

Culicoides midges are most active in the evening and morning, which were the periods of observation in the study. Itching was more prevalent in IBH-affected horses during the evening hours, correlating with the peak activity of Culicoides after sunset.

Movement activity did not differ between IBH-affected horses and controls; however, IBH-affected horses developed excoriations and areas of alopecia from persistent scratching. Even short periods of scratching triggered moderate to severe inflammatory skin lesions. This scratching behavior releases more pro-inflammatory mediators, creating a vicious cycle of inflammation and discomfort, leading to more scratching and itching. Horses not affected by IBH also scratched but did not create self-inflicted skin lesions or wounds.

Management Strategies for IBH-Affected Horses

Prophylactic management strategies, such as using a horse blanket or insect repellent, did not mitigate clinical signs of IBH due to continued exposure to Culicoides. While researchers noted no differences in movement activity or behavior between IBH-affected and control horses, finding effective prophylactic measures to improve horse welfare related to insect hypersensitivity is crucial. Even short periods of exposure to midges lead to self-trauma, creating open wounds and lesions. 

Ideally, preventing exposure to biting midges in the first place involves moving horses to areas less conducive to midge development and breeding habitats, equipping horses with effective fly sheets that cover the belly, and identifying an appropriate insecticidal repellent to keep insects away from a horse’s body. Mosquito traps also prove useful in reducing Culicoides midge populations in the environment.

Conclusion

Insect bite hypersensitivity poses a significant challenge to horse welfare. Proactive management and effective preventive measures are essential to minimize the impact of this condition on horses, preserving their health and value.

Source: https://equimanagement.com/research-medical/improving-the-welfare-of-ibh-affected-horses/?fbclid=IwZXh0bgNhZW0CMTAAAR31kG_0cbeFjecPOiMqNQwVobD1Qf-pzbUHmfDE4_hqa5IIc1n4boQxMUM_aem_SxbCrXOH6sF8cpmwxU6fXQ

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