Molecular mechanisms and treatment modalities in equine Culicoides hypersensitivity

The first record of Culicoides deltus as a putative vector of Onchocerca flexuosa in Slovak red deer (Cervus elaphus)

Within the research conducted in the years 2016-2022 in the area of Volovsky Mountains in Slovakia, 63,950 biting midges were collected during 74 trapping sessions. The aim of the study was to identify species composition of biting midges, their host preference and potential transmission of parasites by these insects under natural conditions. The collected biting midges fell into 29 species and the most common were the Culicoides (C. obsoletus/C. scoticus/C. montanus) that accounted for 47.9% of the collected biting midges. Identification of species was based on the morphology of biting midges and the use of molecular methods. We confirmed positive suckling results on red deer in three samples namely C. montanus, C. scoticus and C. deltus. We examined these samples for the presence of Onchocerca worm DNA. We confirmed the presence of O. flexuosa DNA in one C. deltus sample. The host preference of biting midges was identified by molecular technique that involved sequencing a 350-bp sequence of the mitochondrial cytochrome b gene (cyt b). The presence of Onchocerca flexuosa DNA in C. deltus was confirmed by sequencing of fragments of mitochondrial genes cox1. The sequences matched the previously published sequences for O. flexuosa. Data on high prevalence of infections caused by Onchocerca worms in red deer in Slovakia have already been published and indicated favourable conditions for the vectors and a suitable environment for parasite circulation in Slovakia. According to the authors' knowledge, this was the first ever detection of O. flexuosa in C. deltus in wild nature.

Phenotypic Shift of an Inflammatory Eosinophil Subset into a Steady-State Resident Phenotype after 2 Years of Vaccination against IL-5 in Equine Insect Bite Hypersensitivity

Eosinophils play a key role in allergic diseases such as insect bite hypersensitivity (IBH). Together with Th2 cells, they shape the course of inflammation in associated type I/IVb allergies. Therefore, a virus-like particle (VLP)-based vaccine targeting equine interleukin-5 (eIL-5), eIL-5-CuMV-TT, was developed to interfere with the IL-5 dependency of eosinophils by inducing the production of anti-self-IL-5 antibodies and alleviating clinical signs in IBH-affected horses. A previous study highlighted the presence of two eosinophil subsets, steady-state resident eosinophils (rEos) and inflammatory eosinophils (iEos), circulating in the blood of healthy and IBH-affected horses, distinguishable by the expression of integrin CD49f. Furthermore, eIL-5-CuMV-TT 1st year vaccination showed a significant decrease of total eosinophils and, in particular, iEos. Nevertheless, the very few remaining eosinophils still shared an iEos phenotype, reflected by bigger size and higher granularity. The aim of this study was to follow up on the phenotype of eosinophils in the 2nd year of vaccination of IBH-affected horses with eIL-5-CuMV-TT. Using flow cytometry analysis of the blood of healthy, IBH, IBH-placebo, and IBH-vaccinated horses, the percentage and count of cells were compared between groups with a focus on pair analysis of eosinophils in 1st and 2nd year vaccinated horses. Our data showed comparably low levels of iEos and a significant increase of rEos in 2nd year compared to 1st year vaccinated horses, suggesting a phenotypic shift toward a resident-like eosinophil population, primarily associated with the phenotype of healthy horses. The reduction of size, granularity, and expression of integrin CD49f in the 2nd year suggests a benefit of long-term treatment with the eIL-5-CuMV-TT vaccine.

Cytokines and chemokines skin gene expression in correlation with immune cells in blood and severity in equine insect bite hypersensitivity

Background

Insect bite hypersensitivity (IBH) is the most frequent skin allergy of horses and is highly debilitating, especially in the chronic phase. IBH is caused by IgE-mediated hypersensitivity reactions to culicoides midge bites and an imbalanced immune response that reduces the welfare of affected horses.

Objective

In the present study, we investigated the pathological mechanisms of IBH, aiming to understand the immune cell modulation in acute allergic skin lesions of IBH horses with the goal of finding possible biomarkers for a diagnostic approach to monitor treatment success.

Methods

By qPCR, we quantified the gene expression of cytokines, chemokines, and immune receptors in skin punch biopsies of IBH with different severity levels and healthy horses simultaneously in tandem with the analysis of immune cell counts in the blood.

Results

Our data show an increase in blood eosinophils, monocytes, and basophils with a concomitant, significant increase in associated cytokine, chemokine, and immune cell receptor mRNA expression levels in the lesional skin of IBH horses. Moreover, IL-5Ra, CCR5, IFN-γ, and IL-31Ra were strongly associated with IBH severity, while IL-31 and IL-33 were rather associated with a milder form of IBH. In addition, our data show a strong correlation of basophil cell count in blood with IL-31Ra, IL-5, IL-5Ra, IFN-γ, HRH2, HRH4, CCR3, CCR5, IL-12b, IL-10, IL-1β, and CCL26 mRNA expression in skin punch biopsies of IBH horses.

Conclusion

In summary, several cytokines and chemokines have been found to be associated with disease severity, hence contributing to IBH pathology. These molecules can be used as potential biomarkers to monitor the onset and progression of the disease or even to evaluate and monitor the efficacy of new therapeutic treatments for IBH skin allergy. To our knowledge, this is the first study that investigated immune cells together with a large set of genes related to their biological function, including correlation to disease severity, in a large cohort of healthy and IBH horses.

Insect Bite Hypersensitivity in Horses: Causes, Diagnosis, Scoring and New Therapies

Insect Bite Hypersensitivity (IBH, Queensland itch, sweet itch, equine summer eczema) is the most common pruritic disease of horses. It is most often caused by sensitivity to the saliva of Culicoides spp. of biting midges; however, it can also be caused by hypersensitivity to other insect species. The prevalence of IBH in horses is reported to be as high as 60% in some parts of the world. Due to the severe pruritus and effects of secondary self-trauma, IBH has animal welfare concerns, and there is currently no cure. Management of this condition is life-long, time consuming and costly. New grading systems to document disease severity are being validated, which will allow the comparison of clinical trial results of new and existing therapies. Management involves the minimisation of insect bites by use of stabling, fans, rugs and repellents. Symptomatic therapy involves the administration of systemic or topical corticosteroids, systemic antihistamines, and creams and sprays to promote skin healing and decrease inflammation. New immune-mediated therapeutics including vaccines, in addition to desensitisation procedures, show promise at controlling hypersensitivity reactions. This article will review aetiologic agents, pathophysiology, scoring systems and current and new therapies.

Development of an inhibiting antibody against equine interleukin 5 to treat insect bite hypersensitivity of horses

Insect bite hypersensitivity (IBH) is the most common allergic skin disease of horses. It is caused by insect bites of the Culicoides spp. which mediate a type I/IVb allergy with strong involvement of eosinophil cells. No specific treatment option is available so far. One concept could be the use of a therapeutic antibody targeting equine interleukin 5, the main activator and regulator of eosinophils. Therefore, antibodies were selected by phage display using the naïve human antibody gene libraries HAL9/10, tested in a cellular in vitro inhibition assay and subjected to an in vitro affinity maturation. In total, 28 antibodies were selected by phage display out of which eleven have been found to be inhibiting in the final format as chimeric immunoglobulin G with equine constant domains. The two most promising candidates were further improved by in vitro affinity maturation up to factor 2.5 regarding their binding activity and up to factor 2.0 regarding their inhibition effect. The final antibody named NOL226-2-D10 showed a strong inhibition of the interleukin 5 binding to its receptor (IC₅₀ = 4 nM). Furthermore, a nanomolar binding activity (EC₅₀ = 8.8 nM), stable behavior and satisfactory producibility were demonstrated. This antibody is an excellent candidate for in vivo studies for the treatment of equine IBH.

Severe skin lesions caused by persistent bites of the stable fly Stomoxys calcitrans (Diptera: Muscidae) in a donkey sanctuary of western Spain

Animal sanctuaries are important organisations that promote animal welfare and health as well as social awareness. Following the appearance of several donkeys with severe and distinctive skin lesions in a sanctuary from western Spain in 2021, a multicomponent study was performed to rule out the possible causes. The lesions were mainly concentrated on the extremities and, to a lesser extent, on the face and/or chest. The use of cotton leggings on their extremities as an external barrier to prevent them from bites and treatments with antiparasitic, antiseptic washes and dermatitis lotion showed to be effective measures to improve the donkey lesions. Skin scraping was negative for any relevant causative agents. Histopathological examination of the lesions showed an inflammatory infiltrate at the superficial dermal level, compatible with diffuse chronic dermatitis. A field entomological study was conducted from May to October 2021 to ascertain if any Diptera was responsible for these lesions. Considerable numbers of the stable fly Stomoxys calcitrans were recorded in both sticky traps and decomposing straw bedding. Several species of haematophagous Diptera were also recorded in lower numbers in other traps placed on the farm facilities. According to the entomological data, the location of the bites and clinical signs, it was concluded that S. calcitrans was the main cause of the skin lesions in the donkeys. To our best knowledge, this is the first clinical case of donkeys affected by the stable fly in Spain. For differential diagnosis, a brief discussion of the evidence caused by other biting Diptera groups is provided.