Insect Bite Hypersensitivity in Belgian Warmblood Horses: Prevalence and Risk Factors

240 Original article Vlaams Diergeneeskundig Tijdschrift, 2014, 83 Insect bite hypersensitivity in Belgian warmblood horses: prevalence and risk factors Zomereczeem bij Belgische warmbloedpaarden: prevalentie en risicofactoren L.M. Peeters, S. Janssens, A. Coussé, N. Buys Research groups Livestock Genetics, Department Biosystems, KU Leuven, Kasteelpark Arenberg 20, BE-3001 Heverlee, Belgium [email protected] A BSTRACT Insect bite hypersensitivity (IBH) is an allergic reaction to the bites of certain Culicoides spp. or other insects. In this study, risk factors for IBH in Belgian warmblood horses stabled or graz- ing in Flanders (Belgium) were investigated. IBH records (n=3409) were collected in 2009 and 2011 using a questionnaire and face-to-face interviews. The classification of IBH-affected versus unaffected horses was based on the owner’s statement, and the reported IBH lifetime prevalence was 10%. Thirty eight percent of IBH affected horses had no clinical symptoms at the time of questioning. When only the presence or absence of clinical symptoms at the time of questioning was taken into account, the prevalence of IBH symptoms was 6.2%. Seventy percent of IBH-affected horses were treated with IBH measures to reduce clinical symptoms. Model selection was based on backwards elimination in a logistic regression framework starting with 17 factors. The age of the horse, vegetation of surrounding pasture and stud size were found to be significantly associated with the self-reported IBH status. SAMENVATTING Zomereczeem is een allergische reactie op specifieke antigenen in het speeksel vanCulicoides -muggen of andere insecten. In deze studie werden omgevingsfactoren geïdentificeerd die geassocieerd zijn met het voorkomen van zomereczeem bij Belgische warmbloedpaarden (BWP) in Vlaanderen (België). Daarvoor werden met behulp van een enquête 3409 gegevens over zomereczeem verzameld tijdens sportwedstrijden, BWP-prijskampen en via persoonlijk contact met grote fokkers (stoeterijbezoeken en telefoongesprekken). De paarden werden ingedeeld in “zomereczeempositief” of -negatief op basis van de informatie die door de eigenaars aangereikt werd. De gemiddelde prevalentie van zomereczeem bij BWP bedroeg 10% in Vlaanderen. Zeventig procent van de zomerczeempositieve paarden werd behandeld met preventiemaat- regelen om de symptomen te onderdrukken en 38% van de positieve paarden vertoonde geen symptomen op het moment dat de enquête werd afgenomen. Hierdoor was de gemiddelde prevalentie van merkbare symptomen slechts 6,2%. De volgende risicofactoren voor het optreden van zomereczeem bij BWP werden geïdentificeerd: leeftijd, de methode van datacollectie, de periode waarop de enquête werd afgenomen, de trainingsfrequentie en de vegetatie van de omliggende weiden. Daarenboven beïnvloedde het aantal paarden per eigenaar eveneens de (gerapporteerde) prevalentie van zomereczeem. INTRODUCTION and self-excoriation (Anderson et al., 1988). The wel- fare as well as the commercial value of affected hor- Insect bite hypersensitivity (IBH) is a chronic, re- ses are seriously reduced (Fadok and Greiner, 1990). current, seasonal dermatitis. Worldwide, it is the most Apart from the genetic susceptibility (Lange, 2004, common allergic skin disease in horses (Gortel, 1998). Eriksson et al., 2008, Schurink et al., 2011), multiple IBH represents a hypersensitivity reaction to salivary factors are considered to play a role in the occurrence antigens from Culicoides species and possibly from and severity of symptoms associated with IBH, such other insects. It is characterized by numerous papules as geographical location, habitat, management, nutri- and tufted hair, which is followed by intense pruritus tion, age of the horse and the age of first exposure to Vlaams Diergeneeskundig Tijdschrift, 2014, 83 241 allergens (Halldórsdóttir and Larsen, 1991; O’Neill et rounding vegetation and soil humidity of pastures, al., 2002; Steinman et al., 2003; Pilsworth and Knot- body condition of the horse, housing system and tenbelt, 2004; van Grevenhof et al., 2007). Although horse management (Table 1). Another eight questions many studies have been performed on IBH, most concerning the severity and history of IBH-clinical were performed on a small number of individuals, in- symptoms were answered in case the respondent clas- volving more than one breed and gender (Braverman sified his horse as IBH-affected. The questionnaire et al. 1983; Broström et al., 1987, Halldórsdóttir and was completed for all horses owned by each respon- Larsen 1991, Steinman et al. 2003). dent. Recently, risk factors that might affect IBH pre- Sire and dam of each horse, age, coat color and valence in Dutch Shetland ponies and Dutch Friesian sex were retrieved from the BWP studbook database horses have been identified (Schurink et al., 2012) based on the stud book number (Table 1). If the stud using a large number of IBH records, i.e. 7074 and book number was missing, a custom made program 3453, respectively. These records were collected by implementing pattern matching techniques was used foal inspectors (Schurink et al., 2012), but this ap- to search in the database, based on the name of the proach seems unfit for warmblood populations. horse (Van Geystelen, 2011). Warmblood horses are most commonly used in competitions (dressage, jumping, etc.) and because of their economic value, the overall management might Trait definition of IBH differ from that of ponies. Risk factors for IBH were first studied in Belgian warmblood horses based on The IBH status was based on the owners’ observa- a survey held in 2009 (Peeters et al., 2010). Results tions of typical symptoms of sweet itch, e.g. itching, pointed at effects of vegetation (surrounding the pas- hair loss at tail and manes. If IBH was observed dur- ture), body condition and age on IBH. However, the ing life, the horse was considered affected (status=1). yearly variation and the effect and the role of owners Alternatively, if clinical symptoms had never been in IBH were not investigated, although this is crucial observed by the owner, the horse was classified as information in the framework of breeding, for which IBH-unaffected (status=0). The status of the horse the IBH status of many individual horses is required. at the time of data collection was also recorded and referred to as “Clin_status” (1=currently affected or 0=currently unaffected) MATERIALS AND METHODS For affected horses, the earliest age of symptoms, any IBH measures taken by the owner to suppress the Collection of data and population symptoms and their effectiveness were recorded. The term IBH measure is used for every measure taken by A questionnaire was designed to collect data on horse owners to reduce clinical symptoms, i.e. pre- the IBH status (current and lifetime) of individual ventive and curative measures. All immunosuppres- Belgian warmblood horses, together with informa- sive treatments, e.g. corticosteroids, were grouped as tion on management, environment and any preventive medication. or curative measures taken by the owner. The questionnaire was pre-tested on ten horse owners. The duration for completing the final questionnaire was Data handling and statistical analysis about three minutes per horse. In order to obtain a representative sample of the breeding population of Data were coded and stored in a database (MS Belgian warmblood horses, events were sampled Access) and procedures in SAS (SAS Institute, Cary, from the list of events within each of the years 2009 NC, version 9.2) were used for descriptive and statis- and 2011, and approximately reflect the number of tical analyses. The age of the horses and the number BWP horses in each province. In order to collect in- of horses per owner were transformed in categories. formation simultaneously at events, five investigators Two criteria for categorizing continuous variables were trained for the study by the principal investig- were a) the low number of data in some parts of the ator (Table 1). Data were collected using face-to-face range of the continuous variable and b) a non-linear interviews with horse owners attending breeding association with the dependent variable, which would days (n=6) and sport competitions (n=35) in 2009 require several higher order terms in the model. and 2011 in Flanders (Belgium). Every owner attend- Age was categorized based on biological criteria ing an event was invited by one of the interviewers (development of immune response) and a non-linear to participate in the survey. Owners with more than association. Stud size was categorized in two categor- thirty horses were visited at home due to time con- ies (up to ten horses and > ten horses) so that at least straints at the events. 25% of the horses were in one category. A model was The questionnaire started with individual animal built using logistic regression and aiming for robust- information (name, id-number, age), IBH status of ness rather than causality of associations of factors the horse and time of onset. Twelve questions were with IBH status and with IBH clin_status. Therefore, devoted to background information, such as sur- predictor variables were first screened individually 242 Vlaams Diergeneeskundig Tijdschrift, 2014, 83 Table 1. Description of factors in the study on insect bite hypersensitivity in Belgian warmblood horses. The information refers to individual horses and was collected using a questionnaire and studbook data. Factor Information collected Categories used for analysis Year of questioning

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