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Sweet itch in horses is a common disease of great economic and clinical importance. The aim of this study was to examine the influence of epidemiological- and management-related factors on the clinical signs of sweet itch in a multi equine racial, Germany-wide investigation. Furthermore, the aim was to find the best method of treatment.
First, a survey was conducted using questionnaires. There was a return of 404 evaluable records. Those factors meant to have an effect on the incidence of sweet itch in horses, were then statistically analyzed using univariate and bivariate methods. The most common distributionbased test methods such as the t-test and F-test were utilized, as well as the chi-square test (χ²) test and the regression analysis.
The results of the present study show that compared to stallions, geldings were most affected by sweet itch, as they showed the strongest symptoms (p < 0.02). The average age of onset of the horses was 5.7 years. Differentiations by gender show a significantly earlier onset of stallions (by 3.0 years) compared to geldings. Geldings show symptoms significantly later than mares, namely by 1.7 years. It was also found that the incidence of sweet itch increased in horses of a darker color (50.9 %). It was also clear that chestnuts were represented with nearly 20 %. Gray and dapple gray showed milder symptoms than other coat colors (p < 0.05). Buckskin and palomino horses showed the most severe symptoms of sweet itch of all coat colors (p < 0.05). Furthermore, warm blood horses (69 %) had a high disease rate, followed by draft horses (21 %) and Thoroughbreds (7 %). With the differentiated representation of horse races Shetland's ponies, Icelandic horses and Haflinger as robust horse races with a total of 31.3 % form a big portion of the horses with summer eczema. Considering the severity of summer eczema in relation to race, draft horses had the strongest symptoms of sweet itch.
Furthermore, there were correlations between the degree of eczema and the grazing of horses.
Horses, held on pasture 24 hours a day were affected by sweet itch significantly earlier than other horses. In the present study, no significant influence on summer eczema could be detected in the analysis of the attitude of the horse (p > 0.05). The analysis of the feeding has shown that horses fed with concentrated feed (oats and/or muesli) showed milder symptoms than horses, which were not fed with concentrated feed (p = 0.015). The analysis of the status of deworming demonstrated that horses that have not been dewormed regularly, showed more severe symptoms than horses that were dewormed once a year (p < 0.02).
Regions of the body where sweet itch appeared in the early stages were predominantly the mane and tail, followed by the abdomen. In later onset cases, horses would show symptoms along the linea alba. At the time of this study, the majority of the horses showed symptoms in the mane (91.3 %) and tail (89.4 %). Amazingly, there were also a large number of horses that
had been affected in areas as the face (48 %), ears (46.5 %), the withers (33.7 %), neck (32.2 %) and the inner legs (23.5 %). Furthermore, results show that when withers, trunk or inner legs were affected, the disease had already progressed to a significant stage. At the time of this study 99 % of the horses suffered from itching, 76.5 % with strong expression. Furthermore, the horses showed symptoms such as bald areas (87 %) and dandruff (80 %).
Bloody crusts (74 %) and skin thickening (68.1 %) were seen as a sign of a chronic affection.
With increased age of the horses symptoms of sweet itch worsened. There seems to be a significant correlation between increased duration and worsened symptoms in this disease.
Details were focused of the purchase of the horse. The main attention lay on the skin at the time of the purchase and the purchase investigation. These aspects were analyzed because the horses may already have shown certain skin changes at the time of the purchase but these had not been diagnosed as summer eczema. Surprisingly 41.4 % of the horses already showed
symptoms of the summer eczema at the time of the purchase. Itching manifested at 32.4 % of the horses and in turn hairless areas already showed 30 % at the purchase in the coat. The horses which already had a big number at hairless places in the coat at the time of the purchase later showed significantly stronger symptoms of summer eczema than horses who showed none or merely few hairless areas. Even more clearly it behaved with the itching of the horses. Horses who had strong pruritus at the time of the purchase, later showed a significantly heavier clinical picture than horses with none, light or even medium strong pruritus (p < 0.05). With 25.1 % of the horses a purchase investigation was carried out, however, the veterinarian ascertained skin findings merely with 3.5 % of these horses. 27.5 % of the previous owners reported already existing skin problems. The analysis of the data shows that skin problems played a big role at the time of the purchase. Whether or not this was a deliberate deception on the side of the selling owner cannot be excluded. Furthermore 9.5 % of the horses in the study showed a preexisting illness. 3.8 % of these horses had an allergy, starting from hay- or dust-allergy (2.8 %), dust-mites or feed allergens. A total of 2.0 % of the horses (n = 8) fell ill with a lung illness.
The results of this study show the success of the most common drugs and treatment methods of sweet itch. In principle, it was noticed that a recovery of the syndrome appeared as a result of the treatment of the summer eczema in 72.8 % of the horses. The highest success rate of 70.3 % was achieved by using an eczema blanket. The use of creams was valued at an acceptable success of 40 %. In contrast, the use of homeopathics, repellents and autohaemotherapy showed no significant improvement of the disease. Desensitization induced an improvement of the clinical signs of summer eczema of 5 horses.
Furthermore, there were associations between the exposure to insects and the severity of the symptoms of sweet itch in horses. The analysis of the data showed that 85.1 % of the owners reported a strong insect load. The higher the midges and/or brake load, the worse the symptoms. The study therefore showed that the best prevention and treatment of sweet itch in horses is the minimization of allergen exposure and the associated reduction of the insect load.
The findings of this study show for the first time a representative, multi-breeding overview of the etiology, severity and treatment of summer eczema in examined horse population. All in all it was noticed that in 72.8 % of horses suffering from sweet itch, those treated showed an improvement in symptoms. The best effect, with 70.3 % positive outcome, was visible with the use of a blanket. Creams showed an improvement in 40 % of the treated animals. The use of homeopathy, repellants as well as autoheamotherapy did not show significant improvement of the symptoms. In 5 case studies desensitization proved efficient.
The study shows that the most effective prevention and therapy of sweet itch is minimization of explosion towards the allergen. 85,1 % of the participants in the study recalled an increase of Insects. The higher the insect load, the worse the symptomatic of sweet itch (p < 0,00).
This study provides new insight on the development, manifestation and treatment of sweet itch in different horse breeds. The random sample consisted of 404 participants throughout Germany. Limiting factor to this study was the missing reference toward the entire horse population in Germany. To be able to draw conclusions about the entire horse population one would need a control group. Only then would a concrete statement about the epidemiology of sweet itch be valid. Furthermore the subjectivity of the horse owners as well as the sample choice has to be taken under advisement. There is a possibility that predominantly owner of horses affected more severely with sweet itch participated in the study. As it is a purely written questionnaire the assessment of the horse owner concerning the severity of symptoms as well as the insect load may vary greatly. A combination of a written questionnaire as well as an examination by a veterinarian may lead to more thorough result. Also evaluating the progression of sweet itch over several years would be useful. A questionnaire should be designed that should be filled out by the owner more than once a year to which pictures documenting the symptomatic of sweet itch should be added.