Insect bite hypersensitivity (IBH) is a common summer problem, as Culicoides (i.e. gnats, midges, no-see-ums) and other biting flies become more active. Different than typical insect bites, IBH is caused by an allergic reaction that certain horses have to the insects’ saliva, and clinical signs can range from hives to hair loss.¹ Once you’ve tested for and confirmed IBH, it’s important to talk to your clients about different treatment options to try to ease their horses’ suffering.

Talking About IBH Treatments

Part of why it’s so important to make sure that owners know the causes behind IBH is that some of the best management options are environmental and not medical. Because these biting insects are most active at dawn and dusk, your clients should avoid turning the horses out at those times. When the horses are in the barn, box fans should be set up and kept on to ward off midges with the strong air currents. Regular barn maintenance, like manure removal and refreshing still water, can interrupt the breeding cycle, which cuts down on future bites and allergic reactions.¹

On top of these environmental changes, there are a few options that you can offer for short-term relief and repellency. Through your Covetrus^® Prescription Management storefront, you can recommend dermatological sprays to soothe the irritation, as well as repellents to prevent new bites. Work with your clients to choose the correct repellent, as the active ingredient in most fly sprays, pyrethrin, breaks down when exposed to the ultraviolet light from the sun; a good fly spray will also include sunscreen to lengthen the effectiveness. You can also offer corticosteroids to reduce inflammation.¹

Nutritional Supplements for IBH

In addition to reducing exposure to Culicoides and controlling inflammation and itching, talk to your clients about supplementing omega-3 fatty acids into their horses’ diets. This can help with inflammation throughout the body and bring some relief.² In a study focused on quantifying the effect of omega-3 supplements in horses with IBH, it was found that the supplements helped reduce the lesional area of the skin test response and reduce inflammation without negative side effects.³ Adding these supplements, especially those with EPA and DHA, can be a great long-term approach for clients that have horses with IBH. It also has the added benefit of promoting a healthy hair coat without having to worry about the possible side-effects of corticosteroids.¹

The Future of IBH Treatment

Recently, a major advancement in the understanding of the causative allergens identified 11 Culicoides salivary gland proteins as relevant allergens.⁴ As more work is done into characterizing the allergens responsible for IBH and what mechanisms induce an allergic response to them, researchers get closer to developing treatment strategies such as immunotherapy. An immunization protocol has been developed for preventive allergen immunotherapy, which seems to induce a suitable immune response, but it is too early to tell if these advances will lead to improved treatment and prevention of IBH.⁵

Culicoides as Vectors for Disease in Livestock

For livestock producers, being aware of Culicoide activity is important as they are vectors of several arboviral diseases such as bluetongue and epizootic haemorrhagic disease.⁶ Similar to the lack of understanding and development of treatments for allergic reactions, there is also a lack of effective control methods against Culicoides as vectors.

Have a conversation with livestock producers about reducing exposure. Insecticide pour-on treatments as well as vector-preventive establishments (with openings covered by insecticide-treated nets) are common methods of prevention.⁶ In one study, insecticide ear tags reduced the number of biting midges for up to 21 days.⁷ While none of these methods are guaranteed to totally remove the risk of disease, a combination of strategies may help to reduce risk.

References

1. Kentucky Equine Research Staff. “Insect Bite Hypersensitivity in Horses.” Kentucky Equine Research. Published June 7, 2013. Accessed June 13, 2023. https://ker.com/equinews/insect-bite-hypersensitivity/.
2. Kentucky Equine Research Staff. “Skin Problems in Horses: Culicoides Hypersensitivity.” Kentucky Equine Research. Published May 18, 2016. Accessed June 13, 2023. https://ker.com/equinews/skin-problems-horses-culicoideshypersensitivity/.
3. O’Neill, W., S. McKee, and A. F. Clarke. “Flaxseed (Linum usitatissimum) Supplementation Associated with Reduced Skin Test Lesional Area in Horses with Culicoides Hypersensitivity.” Canadian Journal of Veterinary Research 66, no. 4 (October 2002): 272-277. PMID: 12418783; PMCID: PMC227015. Accessed June 13, 2023. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC227015/.
4. Schaffartzik, A., et al. “Equine Insect Bite Hypersensitivity: What Do We Know?” Veterinary Immunology and Immunopathology 147, no. 3–4 (June 30, 2012): 113-126. Accessed June 13, 2023. https://www.sciencedirect.com/science/article/abs/pii/S0165242712000906.
5. Marti, Eliane, et al. “Immunopathogenesis and Immunotherapy of Culicoides Hypersensitivity in Horses: An Update.” Veterinary Dermatology 32, no. 6 (December 2021): 579-e156. Special Issue: Advances in Veterinary Dermatology, Volume 9, 9th World Congress of Veterinary Dermatology, October 2020 - April 2021 (Virtual), Sydney, Australia. First published November 18, 2021. Accessed June 13, 2023. https://onlinelibrary.wiley.com/doi/full/10.1111/vde.13042.
6. Miranda, Miguel Á. “Case Studies of Vector-Borne Diseases in Livestock: Bluetongue Virus.” In Ecology and Control of Vector-Borne Diseases, 5, 221-271. Published online August 22, 2018. Accessed June 16, 2023.https://www.wageningenacademic.com/doi/pdf/10.3920/978-90-8686-863-6_9.
7. Liebisch, Gabriele, and Arndt Liebisch. “Efficacy of Flectron-eartags (cypermethrin) for control of midges (Culicoides) as the vectors of bluetongue virus in cattle: field studies and biossays.” Deutsche Tierärztliche Wochenschrift 115, no. 6 (2008): 220-230. Accessed June 16, 2023. https://pubmed.ncbi.nlm.nih.gov/18605374/.