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Localized Anaphylactic Reactions |  |
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Allergic rhinitis is manifest by serous nasal discharge and sneezing. It is less common in other animals than in people. Often, it is seasonal, correlating with pollen exposure. Nonseasonal rhinitis may be associated with exposure to ubiquitous allergens, such as molds, danders, bedding, and feeds. Recurrent airway obstruction in horses (
Recurrent Airway Obstruction) may be a sequela of low-grade respiratory allergies. Summer snuffles is a seasonal allergic
rhinitis occurring commonly in Guernsey or Jersey cattle placed on certain types of flowering pastures in late summer and early autumn. Allergic rhinitis can be diagnosed tentatively by the following: 1) identification of eosinophils in the nasal exudate, 2) demonstration of a favorable response to antihistamines, 3) disappearance of signs when the offending allergen is removed, or 4) occasionally, its seasonal nature. Unlike in people, skin testing is not an accurate means to
diagnose nasal allergies in animals. |
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Chronic allergic bronchitis has been best characterized in dogs. A dry, harsh, hacking cough that is easily precipitated by exertion or by pressure on the trachea is a characteristic clinical sign. The disease may be seasonal or occur year-round. Usually, it is not associated with other signs of illness. The bronchial exudate is rich in eosinophils and free of bacteria. Chest radiographs are normal, and there may or may not be a low-grade peripheral eosinophilia. The
condition is treated with bronchial dilators and expectorants (aminophylline and potassium iodide or guaifenesin), which aid in the removal of thick, tenacious mucus. Glucocorticoids dramatically alleviate clinical signs, especially when their use can be limited to certain seasons or to low-dose, alternate-day therapy. Avoidance of the offending allergen(s) usually is not possible because only rarely is it identifiable. |
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Allergic bronchiolitis is most common in cats. It is manifest by a low-grade cough, wheezing, some dyspnea, and increased peribronchiolar density on radiographs, and it may be mistaken for other conditions (allergic asthma or lungworm disease). Early in the course of the disease, clinical signs can be modified by antihistamine therapy, but if the disease increases in severity, moderate to high dosages of corticosteroids may be necessary. The offending allergen usually is
not identified.
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Pulmonary infiltration with eosinophilia (PIE syndrome) occurs most frequently in dogs but has been recognized in all species. It is associated with diffuse inflammatory infiltrates in the lungs and a pronounced peripheral eosinophilia; frequently, the serum globulins are increased. Unlike in allergic bronchitis, affected animals are often dyspneic or tire easily with exercise. Diffuse bronchial exudate contains numerous eosinophils. The specific offending allergen
usually is not identified. Glucocorticoids are the treatment of choice. A PIE-like syndrome is also associated with resident or migratory parasitic infections of the lungs in young animals. |
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Allergic asthma is less common in other animals than in humans. Among animals, it is most frequent in cats, in which the signs are similar to those in humans. It occurs more frequently in summer and after going outdoors; individual attacks can be transient and mild, or protracted and severe (status asthmaticus). Mild attacks may manifest as wheezing and coughing; in severe attacks, there may be expiratory dyspnea,
hyperinflation of the lungs, aerophagia, cyanosis, and frantic attempts to obtain air. |
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Intestinal allergies (food allergies) are principally seen in dogs and cats, particularly kittens. (See also
Food Allergy: Introduction and
Nutrition in Disease Management.)
Allergic gastritis is manifest by vomiting, which occurs 1 to >12 times weekly, within 1-2 hr of eating. The vomitus may be tinged with bile. In cats, vomiting may be the sole sign; dogs may also have loose feces intermittently. Cats and dogs with allergic gastritis are usually healthy except for vomiting, although there can be loss of weight and coat condition in severe cases.
Allergic enteritis is associated with a mild inflammation of the small intestine but with little or no eosinophilia. Feces usually are normal in volume and frequency, but consistency varies from semiformed to watery. They may be extremely odorous, especially in cats. Affected animals may be excessively thin despite good appetite. Skin lesions and poor coat are commonly associated with food allergies in cats but less commonly in
dogs. The allergy often follows bouts of viral, bacterial, or protozoal enteritis (a phenomenon known as allergic breakthrough). Food allergy may be a cause of diarrhea in newly weaned piglets, although the supporting evidence is not clear; the diarrhea is usually treated as an infection rather than an allergy.
Eosinophilic enteritis, the most severe form of allergic intestinal disease, manifests by moderate to severe inflammation of the intestines and a pronounced eosinophilia. Diarrhea, weight loss, and poor coat condition are usually evident. The prevalence of
allergic colitis is greater in cats than in dogs, although in general it is not common. In dogs, it is often associated with frequent defecation and soft, mucus-laden and sometimes bloody feces; in cats, it most frequently manifests by more normal feces coated or spotted with fresh blood. |
| Spike tests and allergen-specific IgE levels should not be used as a first approach to diagnosing food allergies. Both diagnosis and treatment of intestinal allergies is by a strictly controlled diet. Dogs should be fed low-protein feeds that contain as few ingredients as possible. A basic diet of rice, cottage cheese (or tofu), and mutton, supplemented with vitamins and minerals, is a good starting diet. When the signs (usually diarrhea) have disappeared, additional foods can be
introduced one at a time. Commercial prescription diets are also available. Low doses of glucocorticoids given daily or every other day also can provide excellent relief for dogs that are not helped by dietary changes. Allergic enteritis in cats is treated by feeding exclusively meat protein. Ground, cooked turkey and lamb are good hypoallergenic foods for cats. If the cat is not also allergic to these foods, feces, weight, coat quality, and skin lesions improve dramatically within
1-2 wk. Once a response occurs, new foods are introduced one at a time at intervals of ≥2 wk. Kittens with food allergies often grow out of them, while older animals may need hypoallergenic diets for life. |
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Atopic dermatitis is a pruritic, chronic skin disorder that occurs in many species but has been studied mostly in dogs. Animals with atopic dermatitis have a genetic predisposition that leads to excessive production of reaginic (IgE) antibodies. It has been estimated that ~10% of all dogs suffer from atopy, with a breed predisposition in terriers, Dalmatians, and retrievers. Atopic dermatitis of dogs often is due to inhaled allergens, eg, house dust mites, pollens,
molds, and danders, but the predominant infiltration of TH2 cells into skin lesions indicates that a Type IV reaction could be associated with the disease progression. The skin is the target tissue in dogs. Atopic dogs often chew at their feet and axillae. Excessive sweating is especially noticeable in hairless areas. The skin lesions are greatly increased in severity by licking, scratching, flea infestation, and secondary bacterial or yeast infection. Atopic
skin lesions in cats are either miliary (small scabs) and widespread, or larger and more localized. Localized lesions are often pruritic. |
| In cats, food allergens probably are a more common cause of skin lesions than are inhaled allergens. Sweet itch (
Biting Midges) is a seasonal allergic dermatitis of horses associated with certain insect bites, especially night-feeding
Culicoides
. Intensely pruritic lesions appear along the dorsum from the ears to tail head and perianal area. Similar allergic skin reactions to insect bites can be seen about the ears and face of cats and dogs. |
| Treatment consists of identifying the offending allergens by intradermal skin testing combined with antigen-specific IgE assay and eliminating (or avoiding) them whenever possible. The “wheal and flare” reaction seen when the offending allergen is injected into the dermis is a focal manifestation of the allergic state. Hyposensitization consists of an extended series of injections of the offending allergen until improvement is noted; it is effective in ~60% of dogs with atopic
dermatitis. If hyposensitization fails, or is not used, alternate-day glucocorticoid therapy is beneficial. Antihistamines are less effective in stopping the clinical manifestation of the disease. However, many animals improve significantly with antihistamine therapy and, therefore, antihistamines should be tried either before or with corticosteroid therapy. Cyclosporine A can be used locally instead of methylprednisolone in cases of severe disease. |
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