Allergic dermatitis (sweet itch) of Icelandic horses in Sweden: An epidemiological study

Abstract

Summary A survey of allergic dermatitis (sweet itch) in Sweden contained information on 441 Icelandic horses. Results of a questionnaire indicated that approximately 15 per cent of the country's Icelandic horses suffered from the disease. The prevalence of allergic dermatitis was significantly higher among horses imported from Iceland (26.2 per cent) compared to that of Swedish‐born animals (6.7 per cent). In addition, horses born in Iceland were significantly more severely affected than horses born in Sweden. The risk of allergic dermatitis in Sweden appeared to be more than six times higher for horses exported from Iceland to Sweden relative to that of horses originally born in Sweden. The prevalence of disease for horses of seven years or older was 30 per cent for Icelandic‐born individuals as compared to 7.3 per cent for horses born in Sweden. Similarly, the risk of allergic dermatitis in Sweden for horses of seven years or older appeared to be nearly 10 times higher for horses imported from Iceland relative to that of horses born in Sweden. Allergic dermatitis usually appeared during the third grazing season for imported horses and during the fourth season for horses born in Sweden. Furthermore, the course of the disease tended to become worse with time. Analysis of the prevalence of allergic dermatitis relative to gender revealed no significant differences. Certain geographical variations in the prevalence of the disease was also found.

Genetic analysis of insect bite hypersensitivity (summer eczema) in Icelandic horses

“…This is in agreement with the findings of Braverman et al (1983). Most studies, however, found no clear effect of gender on summer eczema (Broströ m et al, 1987;Halldó rsdó ttir and Larsen, 1991;Lange et al, 2005). Those studies included fewer observations and, in most cases, less even distributions of males and females than in our study.…”

“…Broströ m et al (1987) found a prevalence of 6.7% among Swedishborn Icelandic horses, and Halldó rsdó ttir and Larsen (1991) reported that 8.2% of Icelandic horses born in Norway were affected by summer eczema. A similar prevalence of 6.3% was reported for Icelandic horses born in Germany, by Reiher and Bjö rnsdó ttir (2004), whereas Lange et al (2005) found a higher prevalence of 16% among German-born Icelandic horses.…”

“…Several studies have shown effects of the location of the horse on the prevalence of eczema, either in terms of geographic regions (Broströ m et al, 1987) or defined according to altitude (McCaig, 1973;Braverman et al, 1983), habitat or climate van Grevenhof et al, 2007). These factors are assumed to be important for the amount of Culicoides that horses are exposed to.…”

“…Allergic eczema in horses, reflecting a hypersensitivity reaction to biting insects, is known under many names in different countries: 'summer eczema,' 'sweet itch,' 'Queensland itch' or 'allergic dermatitis' are some of the most commonly used names to describe the condition (Broströ m et al, 1987). Sensitive horses react, in particular, against bites of certain species of Culicoides, biting midges of the family Ceratopognidae, order Diptera, which are active during the grazing seasons.…”

“…Affected horses suffer from intense pruritus, especially around the mane, tail and hind areas, and the scratching may sometimes result in open wounds with secondary infections. Severe eczema can make the horse unfit for use as a riding horse (Broströ m et al, 1987).…”