Priest Lake Veterinary Hospital Newsletters
Newsletter for January 2004
Hello friends,
2004 marks our 30 year anniversary serving pets and their people in the Nashville area!
Dr. McCollum and his wife Kathy began our practice in a small house across the street from our present location. In 1985 we expanded into the adjacent dental offices while retaining the original veterinary dog side of the hospital. We are currently in the planning phase of new hospital construction. We have outgrown our current facility and will soon double our current size in a fully equipped, free-standing, modern veterinary hospital. Our new location will be in the immediate area in order to continue to provide your pets with uninterrupted high quality medical care.
I am devoting this entire newsletter to the topic of food and pollen/mold/inhalant allergies...extremely common problems in companion animals today. Rather than just a brief overview, I want to provide you with some in depth scientific details on this extremely important topic.
FOOD ALLERGIES
Food allergy is about 10% as common as pollen/mold allergies in dogs and just about as common as pollen/mold allergies in cats. In food allergy, the pet history is that of a non seasonal itching, with little variation in the intensity of itching from one season to another in most cases. Most reports do not suggest a breed predilection; however, one report indicated an increased relative risk in Labrador Retrievers, West Highland White Terriers, and Cocker Spaniels. The age of onset is variable, from 2 months to 14 years old. One report indicated that most food allergies begin at less than 12 months of age.
The distribution of itching and lesions varies markedly between animals.
Ear canal disease manifesting as itching and secondary infection with bacteria (usually Staphylococcus , Pseudomonas , Proteus , or Escherichia coli ) or yeast ( Malassezia pachydermatis ) are common and may be the only presenting complaint.
Other patterns seen include rubbing the eyes, generalized itching, generalized seborrhea, red lesions, or a distribution pattern that may mimic that of pollen/mold allergies (the feet, face, and undersides) or flea allergy dermatitis (the lower back and hindlegs). The most common areas of involvement include the ears, feet, groin, underarm area, front of forelegs, around the eyes, and the muzzle. The degree of itching is usually moderate to severe. Response to anti-inflammatory steroids varies from poor to excellent.
Food allergy remains a confusing allergy to diagnose because there is no 100% reliable diagnostic test other than a strict food elimination diet.
Blood testing and skin testing for food allergens can be unreliable in some cases. The ideal food elimination diet should be balanced and nutritionally complete and not contain any ingredients that have been fed previously to the animal. Many diets contain novel protein or carbohydrate sources (eg, lamb and rice). However, it is often misunderstood that if any previously fed ingredient is present in the elimination diet, the animal may be allergic to that ingredient and the diet trial will be a failure. The key point in any food elimination diet trial is that only novel food ingredients can be fed.
The trial diet should be fed for up to 3 months. If marked or complete resolution of the itching and clinical signs occurs during the elimination diet trial, food allergy can be suspected. To confirm that a food allergy exists and that the clinical improvement was not just coincidental, the animal must be challenged with the previously fed food ingredients and a relapse of clinical signs must occur. The return of clinical signs after challenge is usually between 1 hour and 14 days, although it is usually within 3 days. Once a food allergy is confirmed, the elimination diet should be reinstituted until clinical signs resolve, which usually takes 14 days. At this point, previously fed individual ingredients should be added to the elimination diet for a period of up to 14 days. If itching increases, the individual ingredient is considered positive for having a causative role in the food allergy. If itching does not increase, the individual ingredient is not considered important in causing the clinical signs.
The number of offending food allergens varies from 1 to 5 ingredients per animal. The most frequently identified causative allergens in canine food allergy include beef, chicken, corn, wheat, soy, and milk. Once the offending allergens are identified, control of the food allergy is by strict avoidance of these offending allergens. Concurrent diseases (such as pollen/mold allergy or flea allergy) may complicate the identification of underlying food allergies. Infrequently, the dog will react to new food allergens as it ages.
Clinical presentations of food allergy in cats include small scabs, hair loss, red lesions, and severe head and neck itching. No breed, sex, or age predilection is seen. Age of onset varies from 3 months to 11 years. In one study, 46% of affected cats became symptomatic at 2 years of age, and Siamese cats represented 30% of the cases.
Response to steroids is variable, but about two-thirds of cats show excellent response to steroids initially. Many cats develop a poor response to steroids with repeated treatments. As with canine food allergy, an elimination diet should be fed for up to 3 months. The elimination diet should not contain any previously fed ingredients. Food elimination diets can be difficult in cats because many cats are often reluctant to change diets. Cats should not be starved or forced into eating a new elimination diet due to the serious nature of liver disease that may be induced by prolonged fasting.
Response time to the elimination diets varies from 1 to 9 weeks. Time until relapse of itching after challenge with the offending food varies from 15 minutes to 10 days. The most frequently identified food allergens in cats include fish, beef, and chicken. Avoidance of the offending allergens will control the clinical signs associated with the food allergy.
Special prescription diets from Hills and Purina are available from veterinarians to test for and to treat food allergies.
ATOPY (Pollen/Mold/inhalant allergies)
Atopy is a very common allergy in dogs, second only to flea allergy in areas where fleas are present. It is a hypersensitivity reaction that affects about 10% of the canine population. Animals with atopy are genetically programmed to become sensitized to allergens in the environment. Allergens are inhaled, absorbed through the skin and possibly the stomach, and cause allergen specific production. The skin is the primary target of inflammation in dogs and cats, although sneezing/runny nose and asthma also occur in about 15% of these animals.
Clinical Findings, Lesions, and Diagnosis:
The strong breed predilection includes Shar Peis, Wirehaired Fox Terriers, Golden Retrievers, West Highland White Terriers, Scottish Terriers, Shih Tzus, Dalmatians, Lhasa Apsos, Boxers, Boston Terriers, and Labrador Retrievers. The age of onset is generally between 6 months and 7 years of age, but most animals have clinical signs by 3 years of age. The condition usually occurs on a seasonal basis initially, but about 75% of affected animals become itchy year round with time. Itching is the characteristic sign of atopy. The feet, face, ears, underarms, and belly are the most frequently affected areas. Lesions develop secondary to self-trauma and include hair loss, redness, scaling, saliva staining on the fur, crusting, sores, and dark pigmentation of the skin. Bacterial skin infection, ear infection, and yeast dermatitis are common secondary complications. Other possible conditions causing these signs include food allergy, flea allergy, contact allergy, mange, bacterial skin infection, and yeast dermatitis. A diagnosis of atopy can be made based on the history, physical examination findings, and ruling out other causes of itching. Confirmation is made based on identification of allergens that are compatible with the season of the itching by utilizing skin or blood tests.
Treatment and Control:
The three therapeutic options available for management of atopy are avoidance of the offending allergens, symptomatic therapy to help control itching, and immunotherapy (ie, allergy shots). The primary reason for pursuing skin or blood testing is to identify the offending allergens in a particular animal, so that specific immunotherapy can be used to reduce the allergic reactions associated with these allergens.
Hyposensitization immunotherapy attempts to increase the ability of the animal to tolerate exposure to inhaled allergens without developing clinical signs. It should be the main form of therapy needed to control itching once the offending allergens have been accurately identified. Although the mode of action of immunotherapy is not completely understood, allergen-specific levels increase when immunotherapy is initiated due to a response to the additional allergen load from the immunotherapy injections. Because of this, it is common to see a mild initial increase in the itching during the first few weeks of treatment. With time, allergen-specific levels decrease.
The criteria for successful hyposensitization include the identification of suitable pets, accurate test results and interpretation, appropriate selection of allergens, adequate control of other factors affecting skin disease and itching, systematic administration of immunotherapy injections, and periodic communication between the owner and veterinarian. The pet must have clinical signs that are problematic, occur for several months a year (preferably greater than 4), and be cooperative enough to receive allergy injections. If anxiety or minimal pain associated with the allergy injections causes fearful reactions from the pet, additional injections will become difficult. The pet owner must be willing to follow instructions accurately, be patient, and be able to communicate effectively with the veterinarian. It is important to emphasize the long-term commitment needed for successful immunotherapy. Most people learn to administer the allergy injections very well, while others may need assistance from a capable friend or veterinary staff member. This adds time, expense, and frustration for some owners. Side effects from allergy vaccines are rare, but owners need to understand the possibility of their occurrence and the additional measures that must be taken if needed.
The need for accurate identification of the offending allergens cannot be overemphasized because incorrect or incomplete identification of the causes of itching will result in less than optimal response to immunotherapy. Each vaccine must be made specifically for an individual animal. The allergen selection is determined by correlating the positive allergens on the test results with the prominent allergens during the time of year when the animal is itching. If allergy test results are positive to pollens that are present at a time of year when the animal is not itching, it indicates that either the allergic reaction is mild and has not caused clinical itching (subthreshold), or that it may be a false-positive reaction. In either situation, the allergen should not be included in the immunotherapy vaccine.
Two primary ongoing concerns regarding the effectiveness of the immunotherapy are owner compliance and the veterinarian's ability to recognize and treat other primary or secondary causes of pruritus. Other common primary causes of itching include flea allergy, food allergy, mange, and contact allergy. These should be ruled out before allergy testing, if possible, and continually watched for as a developing problem during hyposensitization. Common secondary causes of itching include superficial bacterial folliculitis (usually due to Staphylococcus intermedius ), seborrhea, and yeast dermatitis. Symptomatic therapy includes not only specific anti-itch therapy (eg, anti-inflammatory steroids, antihistamines, and topical treatments) but also specific antimicrobial therapy (eg, antibiotics and antifungal agents.)
Vaccine preparation involves selection of individual allergens, their concentrations, and preservatives. Most allergy vaccines are aqueous extracts (water based). Alum-precipitated extracts are no longer used often; they were initially developed to slow absorption, thus lengthening the time between allergy injections, and had an increased incidence of sterile abscesses. Allergen supply companies are required to culture each allergen or vaccine to ensure sterility before to release to a veterinarian.
The main variables involved with hyposensitization immunotherapy, other than allergen selection, are the frequency of the injections and the dosage of allergens given. Allergens are administered by SC injection (under the skin). Oral administration is considered experimental and is less effective than via injection. The number of allergens in an individual allergy vaccine is limited. Currently, 10-18 allergens are commonly accepted as the maximum number. If too many allergens are used in one vaccine, the concentration of each individual allergen is low, and the response may not be adequate. Enough vaccine should be made up to last about 6 months. The potency of most vaccines is considered inadequate after 1 year. Vaccine protocols vary, but they usually have an induction period and a maintenance period. During the induction period, the dosage of allergen injected gradually increases. Once the maximum dosage is given, the maintenance level is continued.
Contact one of our doctors for more information about Prescription allergy diets or allergy testing for your pet.
Best Regards,
Dr. Pennington
priestlake@mindspring.com
http://www.priestlakevet.com
361-4646