Dog's Diseases

Skin Allergy

Skin disease in animals is complicated with many contributing factors. Skin allergies can result from exposure to allergens ingested with the food (food allergy), allergens absorbed from the air through the skin (allergic inhalant dermatitis — atopy) and by the direct contact of the skin with them (contact allergy). Flea bite allergy is relatively uncommon in Hong Kong owing to the life-style that animals enjoy here and the relative ease in which flea infestation can be controlled. Allergies are often a combination of the above with one form being more important than the others. The most frequent sign seen with allergies is itchiness.

Food allergies can best be diagnosed by feeding a hypo-allergenic diet for six weeks. If the allergy signs disappear or improve markedly on this treatment alone then a food allergy would be suspected. The original food should be reintroduced and fed for two weeks. If the allergy signs return during this period then the hypo-allergenic food is reintroduced and fed for a further two weeks. A diagnosis of food allergy is made if the skin returns to normal during this time. The particular foods responsible can be determined by gradually introducing different food types into the diet and seeing which ones cause the skin to react. The best treatment of food allergies is to avoid feeding those food types which the animal reacts to. If this is not possible either because they are unknown or impossible to avoid then the use of anti-inflammatory drug is necessary.

Atopic skin disease is by far the most common skin disease seen in Hong Kong. It was once thought that exposure was through breathing in the allergens but research has shown that the agents responsible are often absorbed from the air through the skin. It is the extremities of an animal that appear to be the most itchy with atopy. Dogs will often lick their paws, rub their faces either with their paws or on objects including the owner's legs, shake their heads, scratch their ears and 'scoot' on the backsides owing to inflamed anal glands.

The diagnosis of atopy of made by a combination of history, clinical signs and laboratory tests which help eliminate the other possible causes of the skin disease. Dogs often develop atopy between the ages of one to three years and initially at least the disease is more prevalent with the change of season. Most dogs will show signs in Spring/Summer while a minority will display the condition in Autumn/Winter. Unfortunately for dogs they actually 'grow into' their allergies. This means that as they get older their allergies become worse.

Atopy like the other allergies discussed cannot be cured. The treatment is aimed at management of the condition so that the animal and enjoy a normal quality of life. There are two basic approached to the management of atopy.

The first involves determining the causative agents and nullifying their effects by a the use of a 'sensitizing drug.' At present there are two types of tests available for determining which allergens are responsible. A blood test can be performed which measures the levels of certain proteins in the blood serum and the other method is to inject micro-doses of up to sixty allergens beneath the dog's skin and then 'read' which of the allergens causes a reaction. A sensitizing agent is manufactured based on the results of the tests and administered to the animal for life (maintenance is achieved with a monthly injection). Approximately twenty-five percent of dogs treated with this method will enjoy a very good result and their allergies can be controlled solely with the injections. Another fifty percent will improve but will still need treatment with other drugs and the final twenty-five percent will show no improvement at all.

The second method is to use a combination of anti-inflammatory drugs, shampoos and antibiotics to control the condition. The currently accepted theory with itchiness in allergic skin disease is that a number of factors are involved and each factor is responsible for a certain amount of itchiness. There is a threshold amount of itchiness that needs to be reached before the dog actually starts to feel itchy and begins to scratch. By using a multi-modal approach the aim is to reduce the total amount of itchiness to below this threshold value without having to use excessive amounts of drugs and thereby reducing the side-effects which can be seen when high doses of drugs are used. The two main anti-inflammatory drugs used are prednisolone (corticosteroid) and cyclosporine. Cyclosporine does not cause the side-effects seen with prednisolone but it is much more expensive.

The most important point to learn about allergic skin disease is that it cannot be cured. It can only be managed but successful management is often possible with a minimal amount of drugs and expense.