Epidemiology of canine atopic dermatitis

Canine atopic dermatitis (CAD) is a chronic, allergic skin disease associated with IgE-mediated reactions to environmental allergens. Atopic dermatitis/eczema in humans shares many similarities with CAD and is an increasing problem in industrialized countries. This increase has been attributed to lifestyle and environment factors. The current knowledge about the epidemiology of CAD is limited. The aim of this thesis was therefore to investigate the incidence of and potential risk factors for the development of CAD. Three of the included studies involve the use of a large animal-insurance database. The database includes information about a large number of healthy and diseased individuals over time, but it was not collected for research purposes and data-quality issues needed to be addressed. A validation of the diagnosis CAD in the insurance database showed that although the vast majority of the recorded cases could be considered allergic, the important differential diagnosis cutaneous adverse food reactions had not been ruled out for many patients. The overall incidence rate of CAD was 1.7 cases per 1000 dog years at risk. Several factors were found to be associated with an increased risk of CAD in the insured population; living in an urban area or in the south of Sweden, being born in the autumn and belonging to a high-risk breed. Furthermore, a spatial analysis showed that the incidence of CAD increased by increasing human population density and increasing annual rainfall, and was decreased in the north of Sweden and if there was no veterinary dermatologist present in the county. Finally, a case-control study was performed where 12 veterinarians collected CAD cases from the three identified high-risk breeds; boxer, bullterrier and West Highland white terrier. The main finding was that feeding a diet containing home-made/ non-commercial ingredients to the bitch during lactation protected her offspring from developing CAD. In conclusion, a strong breed predisposition for CAD was seen. Evidence of an increased incidence of CAD in densely populated areas exists but might be biased by the locations of veterinary dermatologists. The potential of using diet for primary prevention of CAD is interesting but randomized controlled clinical trials are required to support this finding