Abstract
BackgroundCulicoides hypersensitivity (CH) is induced in horses by salivary allergens of Culicoides midges. In Iceland, the causal Culicoides species for CH are not present. Previous epidemiological data indicated that Icelandic horses are more susceptible to CH when they are exported from Iceland and first exposed to Culicoides at adult age. Horses born in countries where Culicoides is endemic, develop the disease less frequently. Here, we established a longitudinal allergy model to identify predictive and diagnostic serological biomarkers of CH.ResultsSixteen adult Icelandic horses from Iceland were imported to the Northeastern United States (US) during the winter and were kept in the same environment with natural Culicoides exposure for the next two years. None of the horses showed clinical allergy during the first summer of Culicoides exposure. In the second summer, 9/16 horses (56%) developed CH. Allergen specific IgE and IgG isotype responses in serum samples were analysed using nine potential Culicoides allergens in a fluorescent bead-based multiplex assay. During the first summer of Culicoides exposure, while all horses were still clinically healthy, Cul o 2 specific IgG3/5 antibodies were higher in horses that developed the allergic disease in the second summer compared to those that did not become allergic (p = 0.043). The difference in Cul o 2 specific IgG3/5 antibodies between the two groups continued to be detectable through fall (p = 0.035) and winter of the first year. During the second summer, clinical signs first appeared and Cul o 3 specific IgG3/5 isotypes were elevated in allergic horses (p = 0.041). Cul o 2 specific IgG5 (p = 0.035), and Cul o 3 specific IgG3/5 (p = 0.043) were increased in late fall of year two when clinical signs started to improve again.ConclusionsOur results identified IgG5 and IgG3/5 antibodies against Cul o 2 and Cul o 3, respectively, as markers for CH during and shortly after the allergy season in the Northeastern US. In addition, Cul o 2 specific IgG3/5 antibodies may be valuable as a predictive biomarker of CH in horses that have been exposed to Culicoides but did not yet develop clinical signs.
Highlights
Culicoides hypersensitivity (CH) is induced in horses by salivary allergens of Culicoides midges
Development of clinical allergy All 16 Culicoides naïve horses included in this two-year study remained clinically healthy during the first summer of natural Culicoides exposure
Several horses started to occasionally rub their mane and/or tail and mild alopecia was observed at the face or chest resulting in a slight elevation of their clinical scores during their first summer in the United States (US)
Summary
Culicoides hypersensitivity (CH) is induced in horses by salivary allergens of Culicoides midges. Horses born in countries where Culicoides is endemic, develop the disease less frequently. Culicoides hypersensitivity (CH) is an allergic disease in adult horses known by several names, such as summer eczema, sweet itch, summer seasonal recurrent dermatitis, insect bite hypersensitivity, and others [1, 2]. Affected horses develop a seasonal recurrent allergic dermatitis. Clinical signs start in spring or early summer while Culicoides are present in the environment and include pruritus, loss of hair, skin irritation, and open wounds. The initially acute dermatitis develops into chronic skin lesions during the summer and as long as the horses are continuously exposed to Culicoides in their environment [3, 5,6,7]. CH is not a life-threatening disease, it massively affects the well-being and performance of the affected horses for an extended time during the summer [2, 8]
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