Flea & Flea Allergy

Fleas have existed as a parasite of animals and humans for hundreds of years with more than 2000 species identified worldwide. While significant advances have been made in understanding the characteristics and biology of these parasites, they continue to pose a challenge for pets and pet owners. The presence of fleas on an animal can cause problems including itching, scratching, hair loss, secondary skin infections and in young or very small animals may result in anemia due to blood loss. Some animals may develop an allergic reaction to the bite of fleas, referred to as flea allergy or flea allergy dermatitis.

Unlike flea infestation, flea allergy requires only an occasional flea bite to produce significant inflammation and itching. In dogs, typical symptoms of flea allergy include itching, scratching, hair loss and papules along the back, rump and tail with involvement of ears and paws less common. Flea allergy in cats typically presents as small crusted eruptions often called miliary dermatitis. Lesions are most often seen along the back, rump and tail base or around the neck but may expand from these areas as problems continue. Hair loss may also be seen in cats, due to itching and excessive licking and may occur on the back, sides and abdomen.

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The diagnosis of flea allergy is sometimes a challenge since fleas are often not found on flea allergic dogs and cats. This is an important feature as many pet owners will assume that fleas or flea allergy are not part of the problem because they never see a parasite. However, since only an occasional flea bite is needed to cause intense itching, the lack of observable fleas can be deceptive. Considering that many flea allergic dogs and cats find, chew or ingest an offending flea, it is easy to understand why this might be true. Because of this phenomenon, it is common for veterinary dermatologists to prescribe flea prevention if flea allergy is suspected.

The choice of flea prevention is incredibly important in flea allergic pets as not all options have the same efficacy, mechanism, speed of activity and duration of effect. One of the most important features of a flea prevention product for a flea allergic animal is that product’s speed of kill. Speed of kill refers to how rapidly a product causes the death of the flea. Since it is the literal injection of flea allergen as a flea bites an animal that causes an allergic response, a product with a rapid speed of kill and a long duration of activity is typically the most effective at management of flea allergy. Talk with your veterinarian or veterinary dermatologist about the best choice for your pet.

Flea Allergy

Flea Allergy FAQs

Flea allergy dermatitis is a common cause of itching and scratching in dogs and cats. Flea allergic dogs are often itchy at the back and rump and base of the tail, and may have hot spots that can become bloody and infected. They may also scratch or chew at other areas including the legs and inner thighs that can be quite intense. Flea allergic cats are also quite itchy with excessive licking and chewing at the back and tail base and scratching around the neck. Cats often develop small crusted bumps (miliary dermatitis) on the back and around the neck.

Importantly, fleas are typically NOT seen on flea allergic dogs and cats, or if present can be in very small numbers making them difficult to find. 

The most important factor in treating flea allergy is using rapid acting flea preventative to eliminate any current fleas and prevent any newly acquired fleas from surviving long enough to bite, transfer saliva and cause reactions. Since flea allergy is often intensely itchy, a veterinarian or veterinary dermatologist may prescribe medications such as cortisone (prednisone, corticosteroids) to provide more immediate itch relief. Antibiotics may also be necessary if a secondary bacterial infection is present.

The symptoms of flea allergy dermatitis can be temporarily relieved with medications such as oral or injectable cortisone (prednisone, corticosteroids) and in some cases antibiotics. Symptoms will return, however, if rapid acting flea prevention is not instituted and any population of fleas or potential exposure is not controlled. Talk to your veterinarian or veterinary dermatologist about the best treatments to use.

Flea allergic pets often itch for a period of time after fleas are gone. Most often this is due to an allergic reaction to the flea saliva transferred from the flea bite more than the presence of fleas themselves. Depending on the degree and severity and complications, including secondary bacterial infection, itchiness may last from days to weeks. Since itching, scratching and chewing can be quite intense in flea allergic pets, it is important to see your veterinarian or veterinary dermatologist as soon as possible to provide the right treatment to help alleviate symptoms.

The most important factor in treating flea allergy dermatitis is removal and prevention of any flea exposure. While difficult to treat without medications and rapid acting flea prevention, tools that can be used at home include frequent bathing to remove fleas and steps to manage and prevent any fleas within the environment.

If fleas are seen in a home or on a family pet, the number of fleas present in the home or outside environment is likely much greater than the ones you see. Ideally, call a pest control company to help eliminate flea populations quickly. If trying to perform this task on your own it is important to treat areas of the environment that would be more likely to have higher flea populations. These include areas that are dark, cool and moist (high humidity). Fleas are unlikely to be in high numbers in summer in the middle of a sunny yard. Instead look for areas of shade and high moisture and organic debris (mulch, pine straw etc.).

The best way to check for fleas on a pet is using a flea comb. Flea combs are specially designed with teeth that are close together so that they catch a flea as you pass them through the hair. While fleas may be found anywhere on the body, combing along the back near the tail and the abdomen may be more likely to find them.

Fleas may be present anywhere on a dog’s body but may gravitate toward those areas that provide greater shelter for them. They can often be found near the rump and back or the abdomen and inside the rear legs.

The most common symptom of both fleas and other types of allergies in pets is itching and scratching. Common areas of the body affected with flea allergy include especially the back, rump and tail base, while environmental and food allergies may be more likely to affect paws, abdomen, armpits face and ears. It is important to recognize, though, that these symptoms may vary on an individual pet and that pets may be both flea allergic AND allergic to other allergens including pollens and foods. Veterinary dermatologists are specially trained to investigate and recognize differences in these allergies and arrive at an appropriate management plan to help alleviate symptoms and provide long term relief.

The best way to know if your home has fleas is to see a flea. Other clues may include itchy pets with characteristic symptoms of flea allergy or flea infestation.


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