Flea bite dermatitis is a skin condition in animals caused by an allergy to flea saliva. It produces itchiness and excessive scratching, which can lead to bare patches and skin lesions. When these insects bite, they inject a small quantity of saliva into the wound; this saliva contains more than 15 different substances that could provoke an allergic reaction in animals. The condition can be caused by a single bite, and so just one insect can produce a severe allergic response and prolonged discomfort in an animal. It is most commonly seen in domestic pets, such as dogs and cats, but other animals can be also be affected.
Fleas are most prevalent in summer and fall, so these seasons have the highest numbers of cases. All breeds of dogs and cats can be affected by flea bite dermatitis, but it is more likely to occur in young animals than in puppies, kittens or older pets. Although infestations can affect any animal, only a minority have this allergy.
The first symptom in an affected animal is likely to be scratching. All pets will scratch from time to time — it is a normal part of animal behavior — but very frequent scratching and chewing at particular places may be a sign of this allergy. Usually the lower back, inner thighs, abdomen and head are the worst affected areas. Fur may be lost from these parts, and the skin may develop tiny red lumps, along with abrasions caused by scratching; after a time it may thicken. The problem may be worse for cats, as their sharp claws can cause more damage to the skin.
Although these symptoms are distressing for the animal, and for its owner, the problem itself is not considered serious. If left untreated, however, heavily scratched areas may become infected. Some bacterial skin infections may be severe, and for this reason, any symptoms of flea bite dermatitis should be investigated as soon as possible.
The symptoms result from the animal’s immune system reacting to an antigen in the flea’s saliva. Confirmation of the condition requires a visit to a veterinarian, who can diagnose it with an intradermal allergy test. The vet injects a little of the antigen into the animal's skin and observes what happens. Basic blood tests are usually less accurate than the intradermal test in diagnosing the problem.
Pet owners can also check for fleas. The insects are more easily spotted in animals with light colored fur, but a useful technique is to stand the animal on a sheet of damp white paper or cloth, and run a fine comb through its fur. The insects, and their dark colored feces, will be clearly visible against the white surface.
Treatment and Prevention
Cool, but not cold, water baths may help a dog suffering from flea bite dermatitis; cats, however, are unlikely to tolerate this. A veterinarian will often prescribe hydrocortisone for allergic animals in order to help relieve some of the itching and redness of the skin. The animal should be monitored for secondary infections, as the scratching tends to open up the sores further, leaving them vulnerable to bacterial and fungal conditions. If infection is suspected, the veterinarian may prescribe antibiotics.
These measures treat the symptoms, but not the cause. The only way to eliminate the condition is to get rid of the fleas. This means using one of the many treatments suitable for the type of pet. Any other pets in the house should also be treated, as the insects can move easily from animal to animal. In addition, it may be necessary to treat parts of the house with a suitable insecticide, in order to destroy eggs and larvae, which may be present in carpets and furniture. Repeat treatments may be required.
Flea Habits and Life Cycle
An understanding of the way fleas develop, behave and reproduce can help to ensure their eradication. Adult females typically live for less than two months, but during that time, an individual insect may lay over 2,000 eggs, at a rate of up to 50 per day. The eggs are laid in the host animal’s fur, but tend to drop off onto carpets, cushions and bedding, which make ideal hiding places for the larvae, when they hatch. They feed mostly on the droppings of the adults, which tend to build up in the same places, and provide them with the iron and protein they need for growth.
In common with other insect larvae, the juveniles pupate, that is, go into an inactive phase within a cocoon, for about two to four weeks before emerging as adults. Although some insecticides can kill the eggs, the cocoons are very resistant. For this reason, several treatments may be required, although vacuuming of likely areas can be effective. Like mosquitoes, the adults feed on blood, but whereas a mosquito feeds only once, fleas do so frequently, throughout their lives. They will tend to migrate to parts of the animal that are difficult for it to reach during grooming, such as the back of the neck, but they are very mobile and can be found anywhere.