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Flea allergy dermatitis (also known as 'flea bite hypersensitivity') is an extremely common pruritic skin disease that is caused by a hypersensitivity to the proteins in the saliva of the flea which is injected into your cat's skin when the flea feeds. There are 15 known allergens in flea saliva, each one is capable of causing an allergic reaction in the cat.
Just one bite from a flea is enough to trigger an allergic reaction in your cat. Flea allergy dermatitis is one of the major causes of miliary dermatitis in cats and is the most common allergy seen in cats as well as being the most common skin disease to affect cats. There is no breed or sex predisposition to flea allergy dermatitis although it is less common for cats under 1 year old to have flea allergy dermatitis.
Fleas can be active year-round in warmer climates, or in the summer months in cooler areas. Numbers tend to peak towards the end of summer and into early autumn.
Symptoms vary depending on the degree of sensitivity. Common symptoms include:
- Frequent scratching, licking and biting of the fur, especially around the neck, on the back and the base of their tail.
- Skin sores, particularly around the neck.
- Raised crusty bumps (papules) or scabs on the skin (miliary dermatitis), this most commonly affects the back, particularly the area closest to the base of the cat's tail.
- Thinning fur in the affected area.
- Severe scratching can damage the skin and lead to secondary bacterial infection. This may present as red and inflamed areas along with an unpleasant odour coming from the skin.
- The presence of fleas or flea dirt (feces). Flea dirt is reddish black, with a similar appearance to a grain of pepper. Fleas and flea feces are easier to spot on light coloured cats.
- If no evidence of fleas can be found on your cat, examination of his bedding may reveal the presence of flea feces. Gently tapping or shaking the bedding over a piece of paper and then spraying it with a light mist of water may show up red staining.
Your veterinarian will perform a physical examination of your cat and obtain a medical history from you. Diagnosis is usually made during examination by the presence of miliary dermatitis around the back and base of the tail and often sores around the neck.
He may also notice fleas and/or flea dirt in your cat's coat. It should be noted though that just one bite is enough to trigger a hypersensitivity and in some cases, no fleas will be found on your cat because he is so efficient at removing them during grooming. This is particularly common in extremely sensitive cats who groom excessively.
Sometimes a piece of white paper will be placed underneath your cat while his fur is gently roughed up. The paper is then sprayed with water, and if any flea dirt is present, it will dissolve, leaving a reddish appearance.
As there are many other causes of miliary dermatitis in cats, your veterinarian may also recommend skin patch testing (or intradermal testing). This involves shaving an area of skin and injecting the area with small amounts of common allergens to see if your cat mounts an allergic response to any.
Specialised blood tests can also confirm flea allergy dermatitis by detecting IgE antibodies in the blood.
Your veterinarian will be able to diagnose flea allergy dermatitis. This can be done visually. Signs of fleas on your cat are a good indicator. However, extremely sensitive cats will have few if any fleas on them. This is due to excessive self-grooming. In such cases, to get a definite diagnosis that your cat is in fact allergic to flea bites and not something else then an intradermal skin testing is required. Treatment involves several areas:
- The only permanent solution for flea allergy dermatitis is to completely eliminate fleas from your cat and the environment, then preventing re-infestation of fleas by regular flea treatment. This involves a two-pronged approach. Treating your cat and treating the environment (including your cat's bedding). Up to 90% of the flea population live off your cat, so if you only treat him and not the home, he will quickly become re-infected. See here for more information on how to control fleas in the home and on your cat. It is important to note that all pets should be treated for fleas at the same time.
- Treating secondary skin infections caused by excessive biting and scratching of the skin. This may involve a course of antibiotics, medicated shampoo and or a topical medication.
- Antihistamines or oral tablets or steroid injections may be prescribed by your veterinarian to control inflammation and reduce itching. Long term steroid use can produce side effects, therefore the dosage should be as small as possible and treatment limited until your cat has healed and the flea problem has been controlled.
- Anti-inflammatory injection to reduce the itching.
- Hyposensitization (desensitisation). This involves injecting minute amounts of flea antigen into the cat in the hope that it will re-programme the immune system so it's not hypersensitive to flea antigen. There is limited success with this treatment, however.
- Antibiotics may be prescribed treat secondary bacterial infection.
- If your cat has been diagnosed with flea allergy dermatitis, he should be treated for tapeworm as ingestion of fleas during grooming can transmit the parasite.
Strict flea control is the best way to avoid/limit your cat's exposure to fleas and therefore flea bite allergy. There are a range of flea products on the market, generally, flea collars are not as effective as the newer topical (or spot on) flea products (Frontline, Revolution, Advantage, Advantix, Advocate) or oral tablets (Comfortis and Capstar) to controlling fleas. I have heard anecdotally (through my own veterinarian) that some flea products are becoming less effective as fleas build up a resistance. Your veterinarian is the best person to speak to in regards to flea control products and what he finds most effective.
- If you are using a topical flea product, avoid shampooing your cat afterwards as this can wash off the product.
- Don't mix flea control products unless your veterinarian recommends it as this can lead to a doubling up of the active ingredients and cause toxicity.
- Never use a flea product designed for dogs on your cat as they contain different ingredients which are highly toxic to cats.
White cat photo courtesy Nottingham Vet School.