[Intradermal and serologic testing for insect bite hypersensitivity in a Dahomey-Ox]. / Intradermaler und serologischer Allergietest zur Abklärung einer Insektenstich-Hypersensitivität bei einem Dahomey-Ochsen.

This case report describes an eosinophilic dermatitis on the prepuce of a Dahomey-Ox caused by an insect bite hypersensitivity against Culicoides spp. To the best of the authors' knowledge, this is the first report describing intradermal allergy and serological testing in cattle.

Horse allergy: Curly Horses can mediate immune tolerance.

American Bashkir Curly Horses are claimed to be hypoallergenic, but this has not been clinically proven. In the present study, the effect of exposure to Curly Horses was investigated in 141 patients allergic to horses by measuring their lung function and nasal patency during Curly Horse contact. Continuous contact with Curly Horses, including riding and brushing, decreased the allergic riders' reactivity as measured by FEV1, PEF, and PNIF. Subsequent visits (up to 40 or more hours of riding) further reduced reactivity to the Curly Horses. Allergic events to horses occurred only in 72 out of 1312 riding hours, mainly in the first ten riding hours.In 41 out of the 141 patients, it was further investigated whether repeated exposure to Curly Horses could induce tolerance to other horses. Patients in the tolerance induction study were tested annually for horse allergy using a nasal provocation test. The tolerance induction study showed that exposure to Curly Horses induced immune tolerance to other horses in 88% of patients who completed the study.To understand the mechanism causing hypoallergenicity, we performed IgE immunoblots to determine whether Curly Horse hairs contain IgE binding proteins. However, no differences in IgE reactivity were found between Curly and non-Curly Horses. Moreover, the immune tolerance induction study patients did not show decreased IgE reactivity to hairs from Curly or non-Curly Horses even though patients had developed tolerance. However, we did find increasing levels of anti-horse IgG antibodies in the study patients.Overall, our data strongly suggests that continuous exposure to Curly Horses can induce immune tolerance, rendering these patients non-reactive to horses. The reason for the reduced clinical allergenicity of Curly Horses remains unclear, but the data suggest that blocking IgG antibodies may be of importance for immune tolerance development.

Microarray molecular mapping of horses with severe asthma.

BACKGROUND: Severe asthma (SA) in horses, resembling human asthma, is a prevalent, debilitating allergic respiratory condition marked by elevated allergen-specific immunoglobulin E (IgE) against environmental proteins; however, research exploring the exposome's influence on IgE profiles is currently limited but holds paramount significance for diagnostic and therapeutic developments. ANIMALS: Thirty-five sports horses were analyzed, consisting of environmentally matched samples from France (5 SA; 6 control), the United States (6 SA; 6 control), and Canada (6 SEA; 6 control). METHODS: This intentional cross-sectional study investigated the sensitization profiles of SA-affected and healthy horses via serological antigen microarray profiling. Partial least square-discriminant analysis (PLS-DA) was used to identify and rank the importance of allergens for class separation (ie, affected/non-affected) as variable influence of projection (VIP), and allergen with commonality internationally established via frequency analysis. RESULTS: PLS-DA models showed high discriminatory power in predicting SA in horses from Canada (area under the curve [AUC] 0.995) and France (AUC 0.867) but poor discriminatory power in horses from the United States (AUC 0.38). Hev b 5.0101, Cyn D, Der p 2, and Rum cr were the only shared allergens across all geographical groups. CONCLUSIONS AND CLINICAL IMPORTANCE: Microarray profiling can identify specific allergenic components associated with SA in horses, while mathematical modeling of this data can be used for disease classification, highlighting the variability of sensitization profiles between geographical locations and emphasizing the importance of local exposure to the prevalence of different allergens. Frequency scoring analysis can identify important variables that contribute to the classification of SA across different geographical regions.

Cross-reactive carbohydrate determinants in atopic and healthy dogs and their influence on allergy test specificity.

BACKGROUND: The selection of allergens for immunotherapy in atopic dogs is often based on serum allergy testing. Cross-reactive carbohydrate determinants (CCDs) are common structures in plant and insect allergens that reportedly induce polysensitisation, reduce agreement between intradermal and serum tests and complicate allergen selection. METHODS: Thirty-four dogs with diagnosed atopic dermatitis and 10 healthy dogs were included in the study. An intradermal test was conducted in atopic dogs, and serum samples from allergic and healthy dogs were analysed for allergen-specific immunoglobulin E (IgE) before and after inhibition of detectable anti-CCD-IgE antibodies. RESULTS: Anti-CCD-IgE antibodies were not found in any of the healthy dogs and no polysensitisation to plant and insect allergens was detected. The agreement between intradermal and serum allergy test results in the atopic dogs with anti-CCD-IgE antibodies improved from slight to fair after blocking the anti-CCD-IgE antibodies. In addition, blocking clearly reduced polysensitisation to plant allergens but not to acarid allergens. LIMITATIONS: Only a limited number of healthy dogs were tested in this study. A gold standard for determining the clinical relevance of IgE sensitisation does not exist. CONCLUSION: Inhibition of anti-CCD-IgE antibodies seems to be of importance to improve serum test specificity for allergen-specific IgE in atopic dogs in relation to intradermal allergy testing.

Retrospective evaluation of hypersensitivity reactions and anaphylaxis in dogs (2003-2014): 86 cases.

OBJECTIVE: To characterize anaphylactic reactions in dogs, including clinical signs, severity, treatments, prognosis, and estimated incidence. To determine whether glucocorticoids influence clinical recovery and survival. DESIGN: Retrospective study between January 1, 2003 and April 28, 2014. SETTING: University teaching hospital. ANIMALS: Eighty-six dogs treated for a type I hypersensitivity reaction. Nineteen dogs fulfilled the criteria for anaphylaxis, and 67 dogs had mild cutaneous reactions. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The estimated incidence was 0.04% for anaphylaxis and 0.15% for mild hypersensitivity reactions. The female:male ratio (2.3:1) was significantly higher (P = 0.032) compared to our source population (ratio of 1:1.158). Vaccines were the most frequent trigger for anaphylaxis (57.9%) and mild hypersensitivity reactions (28.4%). Seventy-four (86%) dogs had cutaneous signs, and 11 (57.9%) dogs with anaphylaxis had no cutaneous signs reported. Forty-two (48.8%) dogs received both an H1 antagonist and a glucocorticoid, 34 (39.5%) dogs received an H1 antagonist only, and 6 (6.9%) dogs received a glucocorticoid only. The majority of the dogs survived, and 1 was euthanized due to complications. Clinical signs associated with nonsurvival included respiratory signs (P = 0.006), particularly respiratory distress (P < 0.00001) and cyanosis (P < 0.00001), and circulatory shock (P = 0.005). The analysis of the interaction between etiology, clinical signs, treatment, and outcome did not show any association between pairs of variables. CONCLUSIONS: In the current study, anaphylaxis had a relatively good prognosis, and cutaneous signs were not always present. Based on the present data, the use of glucocorticoids to treat mild type I hypersensitivity reactions and anaphylaxis in dogs was not associated with clinical improvement or survival.

Modified rush venom immunotherapy in dogs with Hymenoptera hypersensitivity.

BACKGROUND: Hymenoptera envenomation occurs frequently in people and dogs and can trigger anaphylaxis. Venom immunotherapy (VIT) is the only preventive treatment for Hymenoptera hypersensitivity and is indicated for people with severe adverse reactions to insect stings. Rush VIT is an accelerated VIT protocol in people. This has not been reported in dogs. OBJECTIVES: The objective of the study was to evaluate the safety of modified rush VIT. ANIMALS: Twenty client-owned dogs with Hymenoptera hypersensitivity based on a history of adverse reactions to Hymenoptera envenomation and a positive intradermal test to honey bee and/or paper wasp venom. MATERIALS AND METHODS: Dogs received incremental doses of venom via subcutaneous injection one day per week for three consecutive weeks until the maintenance dose was achieved. Vital signs were recorded every 30 min prior to venom administration. Adverse reactions were categorised as localised or grade I-IV systemic reactions. RESULTS: Nineteen of 20 dogs (95%) completed rush VIT. One dog experienced a grade III systemic adverse reaction and was withdrawn from the study. No adverse reactions occurred in 10 of 20 dogs (50%). Localised and grade I-II systemic reactions occurred in nine of 20 dogs (45%), including nausea (n = 5), injection site pruritus (n = 3) and diarrhoea and lethargy (n = 1). CONCLUSIONS AND CLINICAL RELEVANCE: Modified rush VIT in dogs was well-tolerated and should be considered for dogs with Hymenoptera hypersensitivity. Larger studies are needed to evaluate the efficacy of VIT in dogs for preventing hypersensitivity reactions to insect stings.

Sensitivity of a Hymenoptera serological immunoglobulin (Ig)E assay for the diagnosis of venom hypersensitivity in dogs.

BACKGROUND: Hymenoptera envenomation with honey bee (Apis mellifera) and paper wasp (Polistes spp.) may cause life-threatening anaphylaxis in dogs. In human patients, clinical history, intradermal testing (IDT) and measurement of allergen-specific serological immunoglobulin (Ig)E (sIgE) are used to support a diagnosis of Hymenoptera venom hypersensitivity. The utility of venom allergen-specific sIgE has not yet been evaluated for this purpose in dogs. OBJECTIVES: The objective of the study was to investigate the sensitivity (sn), specificity (sp) and positive predictive value (PPV) of honey bee and paper wasp serological titres using a commercially available sIgE assay [VARL (Veterinary Allergen Reference Laboratory) Liquid Gold] against clinical history for a diagnosis of Hymenoptera hypersensitivity in dogs. MATERIALS AND METHODS: Honeybee and paper wasp IgE serum titres were measured in 15 client-owned dogs with a diagnosis of Hymenoptera venom hypersensitivity based on a history of anaphylaxis, owner observation of Hymenoptera, and positive IDT to bee and/or wasp; and in 10 client-owned dogs with no known history of anaphylaxis or Hymenoptera exposure and a negative IDT to bee and wasp. RESULTS: Analysis of receiver operating characteristic (ROC) curves demonstrate that a VARL score cut-off of one of six for honeybee yields Sn, Sp and PPV of 40%, 60% and 60%, respectively, and two of six for wasp yields Sn, Sp and PPV of 25%, 78% and 60%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Owing to the poor sensitivity and PPV of sIgE assays for both bee and wasp hypersensitivity in dogs with known envenomation and anaphylaxis, the use of sIgE cannot be recommended as a tool for venom identification.

A review of cutaneous hypersensitivity reactions in dogs: A diagnostician's guide to allergy.

Allergic dermatoses are common in people and domestic animals. Resultant lesions are routinely biopsied and submitted for histological examination to confirm a diagnosis or rule out diseases with overlapping or atypical clinical features. Diagnostic pathologists and clinicians are often faced with the difficult task of determining whether an allergic reaction pattern is present on both the microscopic and macroscopic levels and correlating histopathologic findings with clinical and historical data to achieve a precise clinical diagnosis. The bulk of the current veterinary literature on allergic dermatoses focuses on atopic dermatitis in dogs, distantly followed by cats, horses, and other animals. The objectives of this review are to demonstrate the key histopathologic and clinical diagnostic features of the various allergy-mediated reaction patterns, and to provide diagnosticians with a practical guide for clinicopathological correlations. Current concepts in the pathophysiology of immediate hypersensitivity reactions, with a focus on atopic dermatitis, are discussed. Points of potential histopathologic overlap between the "classic" allergic reaction pattern and less common inflammatory, predominately eosinophilic, conditions that may mimic this pattern will be discussed with the goal of highlighting the critical need for collaboration between pathologists and clinicians in furthering patient care.

Retrospective review of diphenhydramine vs diphenhydramine plus glucocorticoid for the treatment of allergic reaction in cats.

OBJECTIVES: The aims of the present study were to report the outcomes of treating allergic reactions in cats with diphenhydramine vs diphenhydramine plus glucocorticoid and to determine whether signs recurred or additional veterinary intervention was needed in the days after initial treatment. METHODS: This retrospective study evaluated 73 cats treated for allergic reaction with diphenhydramine alone or in combination with a glucocorticoid at a 24 h emergency and specialty referral veterinary hospital between 1 January 2012 and 31 March 2021. RESULTS: In total, 44 cats were treated with diphenhydramine alone, and 29 were treated with diphenhydramine plus dexamethasone sodium phosphate. The inciting cause was known or highly suspected in 50 patients. Vaccines were the most common (31 patients), followed by insect envenomation (17 cases). No cat in either group progressed to anaphylaxis. There was no difference in resolution of clinical signs between the groups. Follow-up contact was successfully made with 40/73 cat owners. All 40 cats were alive. Eight had persistent signs. There was no difference in the number of cats with persistent signs between groups. Five cats required additional treatment after the initial emergency visit. There was no difference between the two groups for persistent signs at follow-up. CONCLUSIONS AND RELEVANCE: There was no difference in measured outcomes between cats treated with diphenhydramine alone vs those treated with a glucocorticoid in addition to diphenhydramine in this population. The ideal treatment for allergic reactions is unknown. Based on currently available data in human and veterinary literature, glucocorticoids are not indicated to treat acute allergic reactions. The role of antihistamines as part of a symptomatic supportive treatment plan to shorten the duration of signs is unclear at this time and may be considered.

Efficacy and tolerance of a novel topical TRPV-1 channel antagonist in dogs with allergic pododermatitis.

BACKGROUND: Pruritus due to allergic skin disease is one of the most common reasons for dermatological consultations in the veterinary clinic. Treatment is usually multimodal and requires continuous monitoring and reassessment. New therapies are needed to broaden the therapeutic arsenal. HYPOTHESIS/OBJECTIVES: The aim of this study was to evaluate the efficacy of a novel transient receptor potential vanilloid 1 (TRPV1) channel antagonist for allergic pododermatitis in dogs. ANIMALS: Twenty-four client-owned dogs with allergic pododermatitis. MATERIALS AND METHODS: The study was an open, prospective, multi-centre clinical trial with client-owned dogs. All dogs were treated twice daily with a spray containing hydroxymethoxyiodobenzyl glycolamide pelargonate for 28 days. Clinical assessments included pruritus Visual Analog Scale (PVAS), pedal skin lesion score, evaluation of quality of life (QoL), presence of secondary infections and a four-point subjective efficacy assessment by the veterinarian and the dog owner. RESULTS: There was more than 50% improvement in all scores by the conclusion of the study. Secondary infections were reduced (p < 0.001). Both the veterinarians and dog owners evaluated the efficacy of the product positively. The product was well-tolerated. CONCLUSIONS AND CLINICAL RELEVANCE: This study demonstrated the tolerability and efficacy of a TRPV1 antagonist on pruritic pododermatitis in 24 dogs.

Feline heartworm disease and environmental allergens hypersensitivity: is there a link?

BACKGROUND: Cats can be infected by Dirofilaria immitis, the causative agent of heartworm disease, characterized by respiratory signs, airway hyperreactivity, remodelling and inflammation. Allergy is a multifactorial pathology, and the role of a number of helminth parasites in the development of allergies in humans and other species has been demonstrated in many studies. The aim of the present study was to verify whether cats seropositive for D. immitis present hypersensitivity to some environmental allergens. METHODS: Blood samples were collected from 120 cats and tested for the presence of specific immunoglobulin G antibodies against D. immitis and for hypersensitivity to 20 allergens, using commercial allergen test kits. RESULTS: Of the 120 cats tested, 72 (60.0%) were seropositive for anti-D. immitis IgG and 55 (45.8%) showed clinical signs of heartworm disease of a respiratory nature. The results of testing with the allergen kits showed that 50.8% of cats were seropositive for ≥ 1 allergens, with the most common allergens being Dermatophagoides farinae (25.8%), Dermatophagoides pteronyssinus (20.0%), Malassezia (17.5%) and Ctenocephalides felis (14.2%). The prevalence of allergies was significantly higher-by almost threefold-in cats seropositive for D. immitis (68.1% vs. 25%). There were no significant differences between the prevalence of allergic cats and presence/absence of symptoms, and the results confirmed that symptoms were not a decisive factor for the presence of allergies. The risk for developing allergies was 6.3-fold higher in cats seropositive for D. immitis than in cats that were seronegative, confirming that seropositivity for D. immitis is a risk factor. CONCLUSIONS: Cats with confirmed heartworm can develop serious respiratory signs, potentially leading to progression to permanent lung injury and predisposing cats to hyperresponsive airway disease. Previous studies have shown that seropositivity for D. immitis and Wolbachia is related to the presence of bronchoconstriction and bronchospasm in the affected cat. The results support the suspicion that contact with D. immitis may be a risk factor for the presence of allergies.

Equine allergic skin diseases: Clinical consensus guidelines of the World Association for Veterinary Dermatology.

BACKGROUND: Allergic skin diseases are common in horses worldwide. The most common causes are insect bites and environmental allergens. OBJECTIVES: To review the current literature and provide consensus on pathogenesis, diagnosis, treatment and prevention. MATERIALS AND METHODS: The authors reviewed the literature up to November 2022. Results were presented at North America Veterinary Dermatology Forum (2021) and European Veterinary Dermatology Congress (2021). The report was available to member organisations of the World Association for Veterinary Dermatology for feedback. CONCLUSIONS AND CLINICAL RELEVANCE: Insect bite hypersensitivity (IBH) is the best characterised allergic skin disease. An immunoglobulin (Ig)E response against Culicoides salivary antigens is widely documented. Genetics and environmental factors play important roles. Tests with high sensitivity and specificity are lacking, and diagnosis of IBH is based on clinical signs, seasonality and response to insect control. Eosinophils, interleukin (IL)-5 and IL-31 are explored as therapeutic targets. Presently, the most effective treatment is insect avoidance. Existing evidence does not support allergen-specific immunotherapy (ASIT) using commercially available extracts of Culicoides. Hypersensitivity to environmental allergens (atopic dermatitis) is the next most common allergy. A role for IgE is supported by serological investigation, skin test studies and positive response to ASIT. Prospective, controlled, randomised studies are limited, and treatment relies largely on glucocorticoids, antihistamines and ASIT based on retrospective studies. Foods are known triggers for urticaria, yet their role in pruritic dermatitis is unknown. Recurrent urticaria is common in horses, yet our understanding is limited and focussed on IgE and T-helper 2 cell response. Prospective, controlled studies on treatments for urticaria are lacking. Glucocorticoids and antihistamines are primary reported treatments.

IgE-binding monocytes upregulate the coagulation cascade in allergic horses.

IgE-binding monocytes are a rare peripheral immune cell type involved in the allergic response through binding of IgE on their surface. IgE-binding monocytes are present in both healthy and allergic individuals. We performed RNA sequencing to ask how the function of IgE-binding monocytes differs in the context of allergy. Using a large animal model of allergy, equine Culicoides hypersensitivity, we compared the transcriptome of IgE-binding monocytes in allergic and non-allergic horses at two seasonal timepoints: (i) when allergic animals were clinical healthy, in the winter "Remission Phase", and (ii) during chronic disease, in the summer "Clinical Phase". Most transcriptional differences between allergic and non-allergic horses occurred only during the "Remission Phase", suggesting principal differences in monocyte function even in the absence of allergen exposure. F13A1, a subunit of fibrinoligase, was significantly upregulated at both timepoints in allergic horses. This suggested a role for increased fibrin deposition in the coagulation cascade to promote allergic inflammation. IgE-binding monocytes also downregulated CCR10 expression in allergic horses during the "Clinical Phase", suggesting a defect in maintenance of skin homeostasis, which further promotes allergic inflammation. Together, this transcriptional analysis provides valuable clues into the mechanisms used by IgE-binding monocytes in allergic individuals.

Immunoglobulin E-specific allergens against leaf in serum of dogs with clinical features of grass leaf allergy.

BACKGROUND: Grass leaf has been suspected of causing immunoglobulin (Ig)E-mediated immediate hypersensitivity reactions in humans and dogs. However, most studies in this area are case-control studies without in vitro data showing the involvement of IgE in the reaction. Laboratory studies have demonstrated the reactivity to a 50-55 kDa protein with clinical signs immediately after contact with grass leaf material. The clinical findings of dogs with atopic-like dermatitis immediately after contact with grass leaf material suggest the involvement of grass leaves as the allergen source. OBJECTIVES: This study was designed to test the IgE-reactivity of grass leaf proteins in dogs with clinical signs and positive scratch test results against grass leaf material. MATERIALS AND METHODS: The serum of 41 patients with a history of allergy and suspected to grass leaf material was immunoblotted against grass leaf extracts from five suspected grass species. The IgE-positive blots were separated with 2D gel electrophoresis and analysed with mass spectrometry (MS). Commercially supplied proteins were used to validate immunoblot activity. RESULTS: The serum of 25 dogs diagnosed with grass dermatitis had positive IgE-specific immunoblot against one or more grass leaf extracts. The MS data indicated a reactive band at 55 kDa to be beta-amylase or RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) large subunit (RbLS). All tested dog sera showed IgE-reactivity with beta-amylase and some with RbLS. CONCLUSIONS AND CLINICAL RELEVANCE: Canines with clinical signs of grass-related dermatitis had IgE-reactivity against grass leaf proteins. Serum IgE-reactivity to beta-amylase and RuBisCO large subunit may indicate that these proteins act as allergens, possibly causing pruritus and skin lesions.

UK-based multicentre cross-sectional study assessing advice requests veterinary dermatologists received from general practitioners.

BACKGROUND: There is little currently little information available regarding the nature of the advice requests veterinary dermatologists receive from general practitioners. Collation of such data could direct continuing veterinary development in the future. METHODS: Dermatologists completed hand-written recording sheets during or after enquiries. Information recorded included the route of enquiry, nature of advice, material provided, practice type and location, animal signalment, presenting signs, diagnosis/differential diagnosis, treatment and referral recommendations, time taken and if charges were made. RESULTS: Twelve dermatology services recorded 768 advice requests over a 6-month period. Most requests were submitted via email and related to canine dermatology (81%). An average of 9.5 minutes was spent replying to requests. Charges were made in 2% of cases. Advice regarding otitis was most commonly sought, followed by pruritus, alopecia and crusting. The most frequently discussed diagnoses included allergy, otitis, pyoderma, demodicosis, dermatophytosis and neoplasia. Antibiotics, anti-pruritics and topical otic medications were the most commonly discussed therapeutics. LIMITATIONS: This is an initial study and therefore there are limitations involving the depth of the data. Additional studies should be completed which identify why advice is sought, decision-making regarding referral, and if advice should be charged similarly to other disciplines. CONCLUSIONS: These findings highlight that veterinarians mostly frequently seek advice on management of common dermatological problems, including allergy, otitis and pyoderma.

Transcription of interleukin 31 and its receptor by leukocytes after Culicoides sp stimulation is dose dependent but is not exaggerated in allergic horses or correlated with pruritus.

OBJECTIVE: Preliminary evidence supports a role for IL-31 in equine insect bite hypersensitivity (IBH) and pruritus. Our studies investigated IL-31 and IL-31 receptor-α (IL-31RA) transcription in leukocytes from normal and IBH horses in response to Culicoides nubeculosus. ANIMALS: 19 normal and 15 IBH horses were recruited in the summer of 2019 (low-dose study) and 8 normal and 10 IBH horses in the winter of 2022 to 2023 (high-dose study). Normal horses had no history or signs of allergic skin disease, while IBH horses had a history and clinical signs compatible with IBH. Pruritus was scored using a visual analog score or a 1 to 6 grading system. PROCEDURES: Whole blood leukocytes were incubated with saline (0.9% NaCl) solution or C nubeculosus (0.26 µg/mL [low dose]; 5 µg/mL [high dose]). Transcription of IL-31 and IL-31RA was measured by quantitative RT-PCR. RESULTS: Transcription of IL-31 and IL-31RA significantly increased in leukocytes from normal and IBH horses following high-dose C nubeculosus, and no differences were found between populations. Following low-dose C nubeculosus IL-31RA, transcription was increased in both normal and IBH horses, but IL-31 transcription was reduced in normal horses. No positive correlation was found between pruritus scores and IL-31 transcription after low- or high-dose C nubeculosus stimulation. CLINICAL RELEVANCE: Exaggerated IL-31 transcription was not identified in IBH horses, suggesting that dysregulation in IL-31 signaling occurs downstream or in localized tissues or involves regulation by yet unidentified receptor splice variants or IL-31-induced increased sensitivity to other pruritogens. Further studies to understand IL-31 signaling in equine allergic skin disease are needed.

Approach to the pruritic horse.

Pruritus in the horse may be due to several causes, the most common being a hypersensitivity response to salivary proteins in the Culicoides genera, which may coexist with atopic dermatitis, also known as an environmental allergy to pollens, molds, dust, storage mites, etc. Less common etiologies are food allergy and contact allergy, the latter often caused by owners applying various products to the skin. Other ectoparasites, such as Chorioptes mites, may also initiate pruritus. Secondary bacterial infections (usually Staphylococcus spp) may be pruritic in and of themselves. This article reviews the questions that need to be asked of owners to obtain a relevant history, always important for any organ system, but perhaps none more so than the skin. The various clinical findings such as alopecia and crusts and their location on the horse, diagnostic methods such as intradermal or serum testing for allergies, and subsequent hyposensitization are also discussed. Therapeutic options currently available for the potential underlying diseases, in particular for the hypersensitivity reactions to Culicoides spp or environmental allergens, are reviewed with the studies of hyposensitization over the last 40 years, as well as medications that may be effective. While the most common causes of pruritus in the horse are known, the current understanding of the pathophysiology still needs to be investigated, and consequently, the most effective treatments for those causes need to be improved. Newer research is discussed that may eventually add to the diagnostic and therapeutic options currently available for the pruritic horse.

Establishment of a protocol for preventive vaccination against equine insect bite hypersensitivity.

Insect bite hypersensitivity (IBH) is a seasonal dermatitis of horses caused by IgE-mediated reactions to bites of Culicoides midges characterized by an imbalance of T-cell subsets. Iceland is free of the causative species but the prevalence of IBH in exported Icelandic horses is especially high. We have shown that intralymphatic (i.l.) vaccination with r-Culicoides allergens in Aluminum hydroxide (alum) and monophosphoryl lipid A (MPLA) adjuvants induces a desired Th1/regulatory T-cell response. The aim of this study was to compare i.l. to subcutaneous (s.c.) injection. Twelve healthy Icelandic horses were injected, i.l. or s.c., three times with four-week interval, using purified r-Culicoides allergens in alum/MPLA. Serum antibody levels and cytokine profile following in vitro re-stimulation of PBMC were analysed. Comparable allergen-specific IgG antibodies were induced following both routes of vaccinations. The antibodies showed similar capacity to block binding of IgE from IBH-affected horse to the allergens. Upon re-stimulation of PBMC, IL-10 was induced. Horses vaccinated i.l. produced more IFN-γ and less IL-4 as compared to the horses injected s.c., but the difference did not reach significance. It can be concluded that applying the simpler s.c. injection instead of i.l. to obtain a suitable immune response could be option in IBH immunotherapy.

Targeting eosinophils by active vaccination against interleukin-5 reduces basophil counts in horses with insect bite hypersensitivity in the 2nd year of vaccination.

Previously, virus-like particle (VLP)-based self-vaccinations targeting interleukin (IL)-5 or IL-31 have been suggested to treat equine insect bite hypersensitivity (IBH), a seasonal recurrent allergic dermatitis in horses. The IL-5-targeting equine vaccine significantly reduced blood eosinophil counts in horses, similar to human monoclonal antibodies targeting IL-5 or the IL-5 receptor alpha (IL-5Rα). Previous studies in humans have also reported an additional effect on reduction of basophil counts. The aim of the present study was to evaluate whether an equine anti-IL-5 vaccine affected blood basophil counts. Horses with IBH were followed in a 3-year trial consisting of a placebo administered in the 1st year, followed by vaccination using an equine (e)IL-5-VLP vaccine in the 2nd and 3rd years. There was a strong reduction in circulating eosinophil counts after vaccination against IL-5. Additionally, there were reduced basophil counts, but only in the 3rd year of the study, suggesting a bystander effect of the anti-IL-5 vaccine on basophil counts.