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Reviewed by Dr Paul Klenerman, specialist and Professor Brian Lipworth, professor of allergies and respiratory medicine
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What is a pet allergy? The proteins from the hair, saliva or urine of household pets cause an allergic reaction that attacks the eyes and the airways, like hay fever, and can result in asthmatic symptoms. It may also cause atopic dermatitis or a nettle rash. It is often difficult to avoid the allergens that can come from other people's pets or be transported by people who have been in contact with animals. School classes can be overloaded with pet allergens. Most often the allergies are to cats or dogs, but rats, mice, guinea pigs, hamsters, pet birds, horses, cows or poultry can be involved. Why are we allergic to pets? Pet allergens are proteins, which when in contact with the skin or breathed in, cause an allergic reaction that provokes the body into producing histamine. The histamine produces swelling and irritation of the upper airways and causes typical hay fever and asthmatic symptoms. The tendency toward allergic reactions is often hereditary. People who have had asthmatic bronchitis as children in a household with pets, especially a cat, are at a high risk of developing allergies towards cats as they get older. Pets are very important in modern life. When moving house or flat, the chances of the former owners having had a pet are high. It may take months, and in a modern insulated flat years, before the level of allergens are so low that an allergic reaction is not a possibility. If pet allergies are suspected, the new house owner should try to stay away from home for a fortnight to see whether the symptoms disappear. A doctor or specialist could be asked to conduct an allergy test to confirm the diagnosis. What are the signs of pet allergy? When touching the fur or feathers of pets; objects containing pet allergens; or breathing in pet allergens; the following reactions may result:
Often it is enough for the doctor to know when and where the patient got their symptoms. Skin tests and blood samples can confirm the diagnosis. What should I do? If you have allergic symptoms, you should avoid things that provoke them and it is advisable to ensure that in your house:
You have to be aware that there is a huge possibility that you may have to find another home for your pet. If you are in this situation, you should contact the RSPCA and ask them for advice. There are low allergen producing animals, such as furless cats, which may sometimes be OK. (But you may be allergic to cat spit and not cat fur? If you want a black and white cat to stroke, how much fun is a cat without fur?) You should still decorate your house as mentioned above. Even if the animal is only visiting you so that you can check if you are able to live with it, it may still take half a year or more before you develop symptoms. Dogs and cats should be bathed at least once a month in plain water. Remember to dry the animals properly afterwards. It has been proved that a monthly 'cat wash' lowers the level of allergens in the house. But what about fish or turtles? This may sometimes work but then you may be allergic to the food they eat. Rabbits and guinea pigs do not produce so much hair but their urine may cause trouble. They should not live in the house but outside and be cared for by a person without allergies. It is possible to buy anti-allergen filters and special air filtering systems (HEPA). Talk to your doctor or an organization for patients with asthma or allergies before you buy these devices. Keep animals out of bedrooms and public rooms. It would be preferable to keep them outside of the house. Every time you touch a pet, wash your hands thoroughly. What complications are possible?
Pet owners should know it is important to avoid their allergens because of the increase in the risk of developing, or worsening, asthma. The symptoms can be controlled with medication but the allergy itself cannot be removed. For people who have only one allergy, it may be possible to have a tolerance treatment. This desensitisation treatment is a vaccination against the allergen. Exposure to the allergens several times in a period of up to five years will be necessary. What medication is given?
There are three groups of these.
These medicines cause the airways to relax and widen. Examples of those which act for a short time (3 or 4 hours following a single dose) are salbutamol (eg Ventolin) and terbutaline (eg Bricanyl). These medicines are inhaled from a variety of delivery devices, the most familiar being the pressurised metered-dose-inhaler (MDI). When inhaled, these types of medicines work within minutes to open the airways, making breathing easier. Longer-acting beta-2 agonists include salmeterol (Serevent) and formoterol (eg Foradil, Oxis). Their action lasts over 12 hours, making them suitable for twice daily dosage to keep the airways open.
One of the ways in which the size of the airways is naturally controlled is through nerves that connect to the muscles surrounding the airways. The nerve impulses cause the muscles to contract, thus narrowing the airway. Anticholinergic medicines such as ipratropium bromide (Atrovent) block this effect, allowing the airways to open. The size of this effect is fairly small, so it is most noticeable if the airways have already been narrowed by other conditions, such as chronic bronchitis.
These medicines are given by mouth and are less commonly used in Britain because they are more likely to produce side effects than inhaled treatment. They are still in very wide use throughout the world. All three types of bronchodilator can be combined if necessary.
There are three main groups of these.
Corticosteroids (or 'steroids') work to reduce the amount of inflammation within the airways, reducing their tendency to contract. They are usually given as inhaled treatment, although sometimes oral steroid tablets may be required for severe attacks. Although steroids are powerful medicines with many potential side effects their safety in asthma has been well established. It is also important to balance the problems that arise from poorly treated asthma against the improvement in health which occurs when the condition is well treated.
There are two medicines in this group: sodium cromoglicate and nedocromil. They also act to reduce inflammation of the airways. They tend to be best for mild asthma symptoms and are more effective in children than adults. The medicines are given by inhalation and are usually very well tolerated.
Leukotrienes are compounds released by inflammatory cells within the lungs and which have a powerful constricting effect upon the airways. By blocking this effect with these antagonist medicines the constriction is reversed. There are two such medicines currently available: montelukast (Singulair) and zafirlukast (Accolate). |
| Based on a text by Dr Flemming Andersen |
| Last updated 16.02.2005 |
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