Clinical and Serological Studies of Canine Atopic Dermatitis

Canine atopic dermatitis is a skin condition of an allergic origin which usually becomes apparent in dogs between the ages of one and three years. This is a particular problem for Guide Dogs for the Blind Association (GDBA) dogs as this is the age that dogs are finishing training and beginning their working life. Hence much time and money is spent on dogs which may have to be retired early due to this skin condition. Therefore, if dogs likely to go on and develop atopic dermatitis could be identified before beginning their training more efficient use of funds and facilities could be made by trainers and the society. A group of dogs passing through the GDBA kennels were studied for a period of three years. This involved collecting clinical and serological data, with the aim of identifying factors which could be used to isolate dogs likely to develop clinical signs of atopic dermatitis. In addition to GDBA dogs, groups of racing greyhounds, laboratory beagles and pet dogs were also examined in order to identify factors peculiar to the GDBA population. GDBA dogs provided an ideal opportunity to study a large number of dogs in a particular environment with excellent husbandry and recording of clinical histories. Both clinical and serological parameters were studied. Examination of clinical histories revealed that GDBA dogs demonstrating four or more episodes of atopic type skin disease before 15 months of age were at an increased risk of developing atopic dermatitis. Serological studies revealed that serum total IgE concentrations are unrelated to the age or parasite status of a dog. Rather there appears to be a range of serum total IgE concentrations in the canine population with some dogs showing high levels and other low. Although it has been suggested (de Week et al, 1998) that only dogs with high serum total IgE concentrations will go on to develop atopic dermatitis this was not always found to be the case as a number of atopic dogs was found to have low serum total IgE concentrations. Unlike serum total IgE, serum total IgG1 concentrations were found to be significantly higher in dogs affected by atopic dermatitis and/or parasitism. In addition serum total IgG1 concentrations were found to increase in dogs following hyposensitisation therapy and this appeared to be associated with the success of hyposensitisation. It is possible that measurement of serum total IgG1 concentrations could be used as an indicator of the success of hyposensitisation before a clinical improvement becomes apparent. When comparing intradermal skin test results and serological results in the same dogs, results do not often agree, possibly due to the different methodologies involved. Allergen exposure appears to influence antibody levels with dogs in different environments and at different times of year showing different serological results. Although allergen exposure can be assumed to be different in different environments an interesting method of identifying exactly which pollens a dog has been exposed to was developed. This involved examination of faecal samples for their pollen contents and revealed a large variety of pollens. This method could be used in the design of intradermal skin tests or serological tests which to date are primarily based on human pollen exposures. Examination of individual allergen responses revealed that atopic dogs appear more likely to demonstrate higher serological results against mould allergens than non- atopic dogs. This was the case even though very few dogs actually demonstrated positive intradermal skin test results against mould allergens. In summary, this study has disproved a number of hypotheses, including the belief that serum total IgE concentrations depend on the parasite status of an animal, and that it is not possible to compare different serological tests and expect a good correlation. The author has demonstrated that by examining the number of episodes of skin disease in dogs by particular ages, the serological response of individuals to particular allergens, especially moulds, and by assessing serum total IgG1 concentrations it is possible to identify dogs at risk of developing atopic dermatitis