An allergy can be considered an inappropriate reaction by the body to something it is exposed to. That exposure can be from inhalation, skin exposure, oral ingestion or injection (via insect bite or needle) of an offending particle referred to as an allergen. Classically we tend to think of rashes and hives, but reactions can range from an acute hypersensitivity causing facial swelling and congestion to diarrhea and ear infections.
For the sake of this discussion we will address the most common forms of allergies we see in dogs and cats: airborne allergens, food allergens and flea allergens.
Flea allergies are extremely common here in Ontario as there are many cases of fleas in urban, suburban and rural settings. Fleas are carried by their host (raccoon, squirrel, cat, dog) from location to location. The fleas lay their eggs on the host and these eggs fall off in the environment. Outside it would be the soil, inside it would be your furniture, carpets and cracks in hardwood flooring. Any dog can acquire a flea infestation if they pass through an area where flea eggs reside or come into contact with another flea-infested animal.
A dog or cat that has a flea allergy essentially gets a reaction in the skin (scabs and hair loss) wherever they get a flea bite. The most common location for a flea allergy is just above the tail base on the back. The cure is straightforward: get rid of the fleas (commonly using products like Advantage or Revolution). Some pets may require some extra relief, however, and a soothing bath and in some cases oral medication or topical treatment is warranted. Prevention is always better and the products mentioned above as well as the Program and Sentinel products work well.
It is important to realize that we and our pets can develop new allergies as we age. Food allergies only account for one in five allergic cases statistically, and can appear as ear infections or episodes of flatulence and intermittent diarrhea. They can cause other skin problems as well. Although they may not be the most common form, they are usually easily remedied by a change in diet, and if they are the cause, then all of your other methods will fail as long as the pet is being fed the offending food.
Most food allergies and allergies in general are to large irregularly shaped molecules and the biggest offenders are the proteins. There are two kinds of diets to consider: 1. Novel protein diets where the protein source is switched from a common protein source (e.g. beef) to a protein source the pet is less likely to be exposed to (e.g. fish); 2. Hydrolyzed protein diets where the protein has been broken down into little pieces so the body won’t recognize it (e.g. Hill’s z/d). Both can be extremely successful, but in order to know if a diet is going to work or not, the trial must be exclusive to that diet for 8-12 weeks as it takes time for the allergens from the previous diet to be eliminated.
Airborne allergies (Atopy):
These are the most common form of allergy accounting for 80% of all allergic skin disease. Typical distribution is the groin, the armpits, the paws and the ears or any one or combination of those. Owners will see a pet that is very itchy in one or all of these locations. Cats tend to barber their fur while dogs tend to get secondary infections when exposed to a large amount of allergen. There is often seasonality to these reactions as the airborne allergen is often pollen or mold spores and only present at certain times of year. Some pets are allergic to human dander and will have reactions when indoors in the winter. Also, the allergy tends to worsen over successive years.
The best cure for an allergy is to remove the allergen, but with many cases this simply is not possible. Once a pet is allergic they will always have problems with inflammation if exposed to the allergen. With airborne allergens, we need to focus on methods of controlling or reducing the inflammation.
The simplest means is regular bathing when itchy: there are special shampoos designed for weekly use to reduce the amount of allergens in the skin that will provide short term relief. We will often combine this with a diet that is high in omega-3 fatty acids. Most fish-based novel protein diets tend to have this feature anyway, so we’ll often use one of these diets for 8 weeks to see if they provide some extra relief. Antihistamines are great options as well they have few side effects and can potentially provide enough effect to halt the reaction.
Steroids work great against allergies, but we do not like to use steroids long term if we can help it as they have undesirable side effects on the liver, pancreas and adrenal glands. They also drive the appetite and cause weight gain and increased drinking and urination. However, there will be occasions when steroids are needed to get allergic inflammation under control. A good alternative is the medication cyclosporine that also controls inflammation but does not have the same side effects. Unfortunately, this drug is challenging to make in a form that can be given orally, hence it costs more.
Testing to identify the specific allergen can be done either by skin or blood testing. This is ususally done to create a vaccine for hyposensitisation treatment – a method of controlling allergies that has been used since the 1930’s. The success rate is around 65%; it is an excellent option, but owners need to be aware that it may not be successful.
Unfortunately, many pets require additional management when their allergies are at their worst. The allergy creates changes in the skin that can allow bacteria and yeast that are already on the skin naturally to proliferate and create pustules, rashes and crusts. Steroids, antibiotics and other medications may be required in those cases for a short term of treatment. As long as an infection of bacteria or yeast is present, it will be difficult to get the skin rash to resolve.
Lastly, although allergies account for the vast majority of skin problems statistically, there are other skin conditions that can be important. Before we launch into any therapy, some basic skin testing: tape preps (for bacteria and yeast), skin scrapes (for certain forms of mites) and sometimes fungal assays (for ringworm) will be necessary. In difficult cases, skin swab culture of pustules can be required. If the skin problem is not presenting with the typical appearance of an allergy, biopsies may be necessary to identify rarer conditions.
Dogs and cats with skin allergies that have bad chronic rashes and infections are often very sweet pets that love attention because we tend to avoid petting or touching them as much as we used to, and they can sometimes suffer a form of neglect. Do not be afraid of touching your pet with a skin condition: we have very different skin environments from our pets and we rarely share pathogens. Wash your hands after handling, and manage the allergy; they are rarely life threatening and commonly chronic and episodic, so be prepared to be patient – underneath it all it’s still the pet you love.