Topic of the Day

Allergy in Dogs

One of the most common conditions affecting animals is allergy. In the allergic state, the animal's immune system "overreacts" to foreign substances (allergens or antigens) to which it is exposed. These overreactions are manifested in three ways. The most common is itching of the skin, as shown by biting, nibbling, scratching or licking. This itching is either localized (one area) or generalized (all over the animal). Another manifestation involves the respiratory system and may result in coughing, sneezing, and/or wheezing. Sometimes, there may be an associated nasal or ocular (eye) discharge. The third manifestation involves the digestive system, resulting in vomiting or diarrhea.

Types of Allergies

There are five known types of allergies in cats and dogs: contact, flea, food, bacterial, and inhalant. Each of these has some common expressions, and each has some unique features.

One disease that can exacerbate all types of allergy in dogs is hypothyroidism. This is a multifocal disease, but needs to be ruled out in most cases of refractory allergy.

Contact Allergy

Contact allergy is the least common of the five types of allergy. They result in a local reaction of the skin. Examples of contact allergy include reactions to flea collars or to types of bedding, such as wool. If the pet is allergic to such substances, there will be skin irritation and itching at the points of contact. Removal of the contact irritant solves the problem. However, identifying the allergen can require some detective work.

Flea Allergy

Flea allergy is common in animals in the United States, but is uncommon in our immediate area. A normal pet experiences only minor irritation in response to flea bites, often without any itching. On the other hand, the flea allergic animal has a severe, itch-producing reaction when the flea's saliva is deposited in the skin. Just one bite causes such intense itching that the cat or dog may severely scratch or chew itself, leading to the removal of large amounts of hair. There will often be open sores or scabs on the skin, allowing a secondary bacterial infection to begin. The area most commonly involved is over the rump (just in front of the tail).

The most important treatment for flea allergy is to get the pet away from all fleas. The interior and exterior environments must be treated as well as the pet and the pet's immediate environment. We have a few topical treatments that have proven quite effective.

Bacterial Allergy

Staphylococcus (Staph) is a bacterium found on normal animal skin. If the skin is normal and the pet's immune system is normal, Staph causes no problems to its host. However, some animals develop an allergy to this bacterium. When this happens, the pet develops areas of hair loss that look much like ringworm. They are often round and 1/2 to 2 inches in diameter. These same lesions develop in true Staph infection; they are easily treated with certain antibiotics, but the Staph-allergic animal has recurrent "Staph infections." The lesions will usually clear with appropriate antibiotics but return as soon as antibiotics are discontinued. After a while, some animals become resistant to antibiotic treatment.

Treatment of Staph allergy involves antibiotics to control the immediate problem and desensitization with Staph antigen for long-term relief.

Inhalant Allergy

The most common type of allergy is the inhalant type, or atopy. Animals may be allergic to all of the same inhaled allergens that affect humans. These include tree pollens (cedar, ash, oak, etc.), grass pollens (especially Bermuda), weed pollens (ragweed, etc.), molds, mildew, and the house dust mite. Many of these allergies occur seasonally, such as ragweed, cedar, and grass pollens. However, others are with us all the time, such as molds, mildew, and house dust mites. When humans inhale these allergens, we express the allergy as a respiratory problem; it is sometimes called "hay fever." The pet's reaction, however, usually produces severe, generalized itching. In fact, the most common cause of itching in animals is inhalant allergy.

Most pets that have inhalant allergy react to several allergens. If the number is small and they are the seasonal type, itching may last for just a few weeks at a time during one or two periods of the year. If the number of allergens is large or they are they are present year-round, the pet may itch constantly.

Treatment depends largely on the length of the animal's allergy season. It involves three approaches:

1. Anti-inflammatory. Anti-inflammatory therapy will dramatically block the allergic reaction in most cases. Steroids may be given orally or by injection, depending on the circumstances. If steroids are appropriate for your pet, you will be instructed in their proper use. Antihistamines can be of value in treating the allergic animal when they are combined with steroids. In some animals, antihistamines can significantly decrease the amount of steroid needed to provide relief. Fatty acid supplementation can also be implemented with steroids and antihistamine. When the three of them are combined, most allergic animals are significantly improved. This is a non-specific approach, which does not treat the allergy, only the complications of the allergic state (itching).

2. Shampoo therapy. Frequent bathing with a hypoallergenic shampoo helps many animals considerably. It has been demonstrated that some allergens may be absorbed through the skin. Frequent bathing is thought to reduce the amount of antigen exposure through this route. In addition to removing surface antigen, bathing alone will provide some temporary relief from itching and may allow the use of a lower dose of steroids.

3. Hyposensitization. The third major form of allergy treatment is hyposensitization with specific antigen injections (or "allergy shots"). Once the specific sources of allergy are identified, very small amounts of the antigen are injected weekly. The purpose of this therapy is to reprogram the body's immune system. It is hoped that as time passes, the immune system will become less reactive to the problem-causing allergens. If hyposensitization appears to help the pet, injections will continue for several years. For most animals, a realistic goal is for the itching to be significantly reduced in severity; in some pets, itching may completely resolve. Generally, steroids are only used on a brief and intermittent basis. This therapeutic approach is recommended for cat or dog that has year round itching caused by inhalant allergy. This approach is not successful with food allergy.

Although hyposensitization is the ideal way to treat inhalant allergy, it does have some drawbacks and may not be the best choice in certain circumstances and for these reasons:

1. Cost: This is the most expensive form of treatment in the short term; however, in the long term, the successfully hyposensitized animal will not need as frequent exams and treatments!!!!

2. Age of Patient: Because many animals develop additional allergies as they get older, younger cats and dogs may need to be retested 1-3 years later.

3. Success Rate: About 50% of animals will have an excellent response. About 25% get partial to good response. About 25% get little or no response. The same statistics are true for people undergoing desensitization.

4. Food Allergies: Although tests for food allergy are available, the reliability of the test is so low that it is not recommended at this time. A food trial remains the best diagnostic test for food allergy.

5. Time of Response: The time until apparent response may be 2-5 months, or longer.

6. Interference of steroids: Many tests require that animals must not receive oral steroids or antihistamines for 2 weeks, or injectable steroids for 6 weeks prior to testing as these drugs will interfere with the test results. However, newer testing methods allow steroid and antihistamine treatment up to the time of testing.

Food Allergy

Cats and dogs are not likely to be born with food allergies. More commonly, they develop allergies to food products they have eaten for a long time. The allergy most frequently develops in response to the protein component of the food; for example, beef, pork, chicken, or turkey. Food allergy may produce any of the clinical signs previously discussed, including itching, digestive disorders, and respiratory distress. We recommend testing for food allergy when the clinical signs have been present for several months, when the animal has a poor response to steroids, or when a very young pet itches without other apparent causes of allergy. Testing is done with a special hypoallergenic diet. Because it takes at least 8 weeks for all other food products to get out of the system, the pet must eat the special diet exclusively for 8-12 weeks (or more). If positive response occurs, you will be instructed on how to proceed. If the diet is not fed exclusively, it will not be a meaningful test. We cannot overemphasize this. If any types of table food, treats or certain vitamins are given, these must be discontinued during the testing period. There may be problems with certain types of chewable heartworm preventative, as well. Your veterinarian will discuss this with you.

If you have any further questions, don't hesitate to ask!