If you or I suffer from allergy we are likely to have itchy eyes and a runny nose or worse, lung congestion. When dogs and cats have allergic reactions they get itchy skin. Really itchy skin. So itchy that they damage themselves and develop a whole range of additional secondary complications such as bacterial or fungal infections. Allergic skin inflammation (dermatitis) is not only caused by external parasites or physical contact with irritants such as grass sap. Simply inhaling allergens such as pollens or eating foods a pet is allergic to can cause itchy skin. Even the presence of certain normal bacteria on the skin can provide an itchy response. These are the commonest causes of allergic itch:
Flea Allergy Dermatitis
This most common of all cat and dog allergies is triggered by an allergic reaction to substances in flea saliva, left after a flea has a blood meal. Itching begins immediately. If your pet is scratching, has no signs of skin damage and you know fleas are about, assume a flea has caused the itch. Flea allergy dermatitis (FAD) initially causes scratching followed by red raised pimples. These are most likely to occur over the rump and in the groin. Eventually the skin becomes thickened, darkened and either dry, sticky or scaly.
Diagnosis and treatment
Finding a flea is of course diagnostic but in the absence of finding one, vigorously rub the coat while your pet stands on white paper. This causes both shiny black flea droppings and possibly flea eggs to become dislodged. An ELISA blood test or intradermal skin test can be used to confirm flea allergy. Treatment involves eliminating fleas and preventing their return. Your pet and its environment are treated. If your pet suffers from FAD don’t rely on biological flea control products that prevent fleas from reproducing. Your objective is to kill fleas as quickly as possible, to prevent them from sucking further meals and provoking more allergic response. We use insecticides such as Frontline, Stronghold or Advantage preventatively on all your livestock – dogs and cats - beginning at least a month before the flea season begins in April.
Atopic Dermatitis - Atopy
This is the second most common form of allergic skin disease. Allergens such as dust mite droppings, human dander or seasonal pollens, either inhaled or simply settling on the skin provoke an excessive antibody immune response, triggering inflammation and itchiness. Atopy takes time to develop and typically starts in dogs and cats from six months to three years of age. The ears, one of the most sensitive parts of the skin, are often the first area to become itchy and inflamed. Licking the paws, groin or axillae or licking the paws then rubbing the face leads to mahogany staining, a sign of chronic irritation. Bacterial complication is common, leading to pustules, crusts, erosions and ulcers.
Diagnosis and treatment
Atopy is frequently complicated by secondary bacterial or fungal infection. Skin cytology diagnoses atopy while fungal and bacterial cultures identify the opportunist microbes. We will dispense appropriate medicated shampoos and antibiotics to control secondary infection. A good long history-taking and clinical evidence from a full year of changing seasons offers the best information for an accurate diagnosis. We use intradermal skin testing and ELISA testing for finding the specific causes of atopic dermatitis. Antihistamines reduce itchiness in some dogs although only in a minority. Corticosteroids are excellent when used sparingly. With experience we can show you how to use them at a low dose for only a few days to nip problems in the bud before secondary infection occurs. Avoiding known allergens is of course the treatment of choice but when that is not possible, dietary supplementation with essential fatty acids found in evening primrose oil, marine fish oil or linseed oil (EPA and DHA fatty acids) may reduce inflammation and itch. Routine bathing and the use of humectants physically cleanses the skin of potential allergens and developing scale in which bacteria and fungi thrive. We often use desensitising vaccines, containing the allergens to which your pet is sensitive. These are quite effective in about one third to one half of cases of atopy.
Food Allergy Dermatitis
This is an underestimated cause of itchy skin disease. The immune system's unfortunate response is the same as for atopic dermatitis. Irritating chemicals are released that cause your pet to scratch and lick. This leads to papules, then pustules and if untreated erosion and ulceration. A rash very often involves the ears and groin but can occur anywhere on the body.
Diagnosis and treatment
A presumptive diagnosis of food allergy is made when a unique protein (hypoallergenic) diet is fed and the condition resolves. (A definitive diagnosis is made only if itchiness returns when previous foods are reintroduced.) Home prepared food is best but often difficult and inconsistent so a good alternative is a commercially prepared hypoallergenic diet. Be careful. There are many on the market and not all are exactly what they say they are. Ashley McManus, our Nutrition Nurse will give individual advice. A hypoallegenic exclusion diet must be fed for at least six weeks to make a confirmed diagnosis of food allergy dermatitis.
Allergic Contact Dermatitis
These itchy skin conditions develop on the least hairy parts of the body, the chin, belly, feet and scrotum after frequent contact with allergens such as grass sap or a single contact with irritating substances (even regular shampoos). The condition causes inflammation leading to pus-filled pimples and bacterial skin disease. Contact dermatitis can develop to seemingly innocuous items such as plastic or rubber food bowls, flea collars, fabric dyes, leather, even drugs such as neomycin, commonly used in ear medicines. A diagnosis is based on the clinical history. Treatment involves removing the cause of irritation and treating any residual inflammation and secondary infection with anti-inflammatories, antihistamines and antibiotics as necessary.