Allergic rhinitis is inflammation of the mucous membrane of the nose caused by a variety of air-borne allergens. An allergy is a specific reaction of the body's immune system to a normally harmless substance, one that does not bother most animals. Dogs who have allergies often are sensitive to more than one substance. Types of allergens that cause allergic reactions include pollen, house dust mites, mold spores, food, latex rubber, insect venom, human dander, medications. Exposure to allergens at times when the body's defenses are lowered or weakened, such as after a viral infection or during pregnancy, seems to contribute to developing allergies. The current thinking is that some dogs inherit a tendency to be allergic from one or both parents. This means they are more likely to have allergies, although they do not inherit a tendency to be allergic to any specific allergen. Large-breed dogs have a higher risk in the development of inflammatory rhinitis.
Normally, the immune system functions as the body's defense against invading germs such as bacteria
and viruses. In most allergic reactions, however, the immune system is responding to a false alarm. When an allergic dog first comes into contact with an allergen, the immune system treats the allergen as an invader and gets ready to attack. The immune system does this by generating large amounts of a type of antibody called immunoglobulin E, or IgE. Each IgE antibody is specific for one particular substance. In the case of pollen allergy, each antibody is specific for one type of pollen. For example, the immune system may produce one type of antibody to react against oak pollen and another against ragweed pollen. The IgE molecules are special because IgE is the only type of antibody that attaches tightly to the body's mast cells, which are tissue cells, and to basophils, which are blood cells. When the allergen next encounters its specific IgE, it attaches to the antibody like a key fitting into a lock. This action signals the cell to which the IgE is attached to release (and, in some cases, to produce) powerful chemicals like histamine, which cause inflammation. These chemicals act on tissues in various parts of the body, such as the respiratory system, and cause the symptoms of allergy. In sensitive dogs, as soon as the allergen lands on the lining inside the nose, a chain reaction occurs that leads the mast cells in these tissues to release histamine and other chemicals. The powerful chemicals contract certain cells that line some small blood vessels in the nose. This allows fluids to escape, which causes the nasal passages to swell-resulting in nasal congestion. Histamine also can cause sneezing, itching, irritation, and excess mucus production, which can result in allergic rhinitis.
House-dust mites are universal in areas of high humidity (most areas of the United States), but are usually not present at high altitudes or in arid areas unless moisture is added to the indoor air. Mites depend on atmospheric moisture and human dander for survival. High levels of mites can be found in dust from mattresses, pillows, carpets, upholstered furniture, bed covers, clothes, and soft toys. The patient's bed is the most important source of dust mites to control. Chemical agents are available for killing mites and denaturing the antigen; however, the effects are not dramatic and do not appear to be maintained for long periods. Therefore, use of these agents in the homes of house-dust mite-sensitive dogs are not recommended routinely. Vacuuming removes mite allergen from carpets but is inefficient at removing live mites.
Skin tests are one way of measuring the level of IgE antibody in a dog. With a positive reaction, a small, raised, reddened area, called a wheal (hive), with a surrounding flush, called a flare, will appear at the test site. The size of the wheal can give the veterinarian an important diagnostic clue, but a positive reaction does not prove that a particular allergen is the cause of symptoms. Although such a reaction indicates that IgE antibody to a specific allergen is present, respiratory symptoms do not necessarily result. There are other diagnostic tests that use a blood sample to detect levels of IgE antibody to a particular allergen. Unless a systematic approach is used, evaluation of a patient with rhinitis can be frustrating to the veterinary practitioner. Diagnostic techniques include obtaining a complete history, performing a thorough physical and oral examination, culture of nasal discharge, nasal radiographs, and rhinoscopy. Treatment is focused on removing the allergen or removing the animal from the allergen. Treatment with corticosteroids to block the hypersensitivity reaction is a consideration.
Methods of Prevention and Control of Repiratory Allergies
Recommended mite control measures are listed below:
- Encase the dog bed in an allergen-impermeable cover and wash it weekly.
- Wash bedding weekly in hot water. A temperature of more than 130 F is necessary for killing house-dust mites.
- Reduce indoor humidity to less than 50 percent.
- Remove carpets where possible.
- Do not allow your pet to sleep on upholstered furniture.
- Remove from the home carpets that are laid on concrete.
- Minimize the number of stuffed toys and wash the toys weekly in hot water.
Indoor fungi (molds) are particularly prominent in humid environments and homes that have dampness problems. Pets living in homes with dampness have increased respiratory symptoms. Measures to control dampness or fungal growth in the home may be beneficial. Reduce exposure of your pets to outdoor allergens (tree, grass, and weed pollens and seasonal mold spores) by keeping them indoors, particularly during the midday and afternoon when pollen and some spore counts are highest.
Vacuuming carpets once or twice a week is essential to reduce accumulation of house dust. Pets sensitive to components of house dust should be kept out of rooms where a vacuum cleaner is being or has just been used. Use a cleaner fitted with a HEPA (high-efficiency particulate air) filter or with a double bag.
Humidifiers and evaporative (swamp) coolers are not recommended for use in the homes of house-dust mite-sensitive pets. These are potentially harmful because increased humidity may encourage the growth of both mold and house-dust mites. In addition, humidifiers may pose a problem if not properly cleaned because they can harbor and aerosolize mold spores.
Indoor air-cleaning devices cannot substitute for the more effective measures described previously. However, air-cleaning devices (i.e., HEPA and electrostatic precipitating filters) have been shown to reduce particulate tobacco smoke. Air cleaners cannot significantly reduce exposure to house-dust mite and cockroach allergens because these heavy particles do not remain airborne. Air-duct cleaning of heating/ventilation/air conditioning systems has been reported to decrease levels of airborne fungi in residences.
- Human Dander as a Potential Allergen Source in Atopic Dogs - Allergen Characterization and IgE-Profiling. Nicole Resk
- Airborne Allergens. (National Institute of Allergy and Infectious Diseases)
- Guidelines for the Diagnosis and Management of Asthma, Clinical Practice Guidelines (National Heart, Lung, and Blood Institute NIH Publication No. 97-4051 July 1997)
- Clinical findings, rhinoscopy and histological evaluation of 54 dogs with chronic nasal disease