Flea allergy: what a pet parent must know

By dnp-team On Jun 15, 2011

Fleas are cosmopolitan ectoparasites with a large variety of hosts. For companion animals and humans, Cat flea (Ctenocephalides felis) and dog flea (Ctenocephalides canis) represent the most important species worldwide. Apart from causing flea allergy dermatitis (FAD), the ability of fleas to function as vectors for disease pathogens, such as Rickettsia & Bartonella spp. bacteria, Dipylidium caninum (dog tape worm) and some viral pathogens is gaining attention. Let’s know more about them.

What are fleas?

Fleas are small (1.5 to 3.3 mm long), agile, usually dark coloured, wingless insects with tube-like mouth-parts adapted to feeding on the blood of their hosts. Their legs are long, the hind pair well adapted for jumping: a flea can jump vertically up to 1.8 m and horizontally up to 3.3 m. This is around 200 times their own body length, making the flea one of the best jumpers of all known animals (relative to body size), second only to the froghopper.

Why should you know about its life cycle?

In order to understand how and why treatment options work, it is important to understand the flea’s life cycle, since various modern treatment and prevention products work on different parts of this life cycle. The flea developmental cycle can be completed in as little as 14 days or last up to 140 days, depending mainly on temperature and humidity. There are several stages to its life cycle: egg, larva or caterpillar, pupa or cocoon, and adult. The length of time it takes to complete this cycle varies depending upon the environmental conditions such as temperature, humidity, and the availability of a nourishing host. Yes… the various flea stages are quite resistant to freezing temperatures.

What is a flea bite?

Flea allergy dermatitis (FAD) or flea bite hypersensitivity is the most common dermatologic disease of domestic dogs. Cats are also afflicted with FAD, which is one of the major causes of feline military dermatitis. Flea allergy dermatitis is caused by flea bites, specifically the saliva of the flea. It is a very itchy condition and predisposes to the development of secondary skin infections. Oddly enough, most animals with flea allergy have very few fleas – because they are so itchy, they groom themselves excessively, eliminating any evidence of fleas. However, a couple of flea bites every two weeks are sufficient to make a flea allergic dog itchy all the time. Any animal can become allergic to fleas, although some dogs are more attractive to fleas than others. While feeding, fleas inject saliva that contains a variety of histamine-like compounds, enzymes, polypeptides, and amino acids that span a wide range of sizes (40-60 kD) and induce Type I, Type IV, and basophil hypersensitivity. Flea-naive dogs exposed intermittently to flea bites develop either immediate (15 minutes) or delayed (24-48 hours) reactions, or both, and detectable levels of both circulating IgE and IgG antiflea antibodies.

Flea bite injecting saliva leading
to development of flea allergy dermatitis

Clinical signs associated with FAD are variable and depended on frequency of flea exposure, duration of disease, presence of secondary or other concurrent skin disease, degree of hypersensitivity, and effects of previous or current treatment. Non-allergic animals may have few clinical signs other than occasional scratching due to annoyance of flea bites. Those who are allergic will typically have a dermatitis that is characterised by pruritus.

In dogs, the pruritus associated with FAD can be intense and may manifest over the entire body.
Classic clinical signs are papulocrustous lesions distributed on the lower back, tailhead, and posterior and inner thighs. Dogs may be particularly sensitive in the flanks, caudal and medial thighs, ventral abdomen, lower back, neck and ears.
Affected dogs are likely to be restless and uncomfortable, spending much time scratching, licking, rubbing, chewing, and even nibbling at the skin.
Hair may be stained brown from the licking and is often broken off.
Common secondary lesions include areas of alopecia, erythema, hyperpigmented skin, scaling, papules, and broken papules covered with reddish brown crusts. The rump and tailhead areas are typically the first and most evident areas affected.
As FAD progresses and becomes chronic, the areas become alopecic, lichenified, and hyperpigmented and the dog develops secondary bacterial and yeast infections.
In extremely hypersensitive dogs, extensive areas of alopecia, erythema, and self-trauma are evident. Traumatic moist dermatitis (hot spots) can also occur.
As the disease becomes chronic, the dog may develop generalized alopecia, severe seborrhea, hyperkeratosis, and hyperpigmentation.

How is it diagnosed?

Flea allergy dermatitis is a common cause of itchiness and scratching in dogs, but other medical problems can lead to similar symptoms. Other disorders that must be excluded are: Food allergy , Atopy, Trauma or other cause of local skin irritation, Sarcoptic mange, Cheyletiellosis (a mite infestation), Otitis externa (ear infection) and Primary keratinization defects.
Other test options are:

A complete medical history including questions about itchiness, areas of involvement, prior history of skin problems, diet, response to therapy, and any concurrent medical conditions.
A thorough physical examination, including examination of the skin.
Fecal flotation tests to determine the presence of concurrent gastrointestinal parasites or identify tapeworms, which are transmitted via fleas.
Skin scrapings examined under the microscope to detect mange mites (sarcoptes, cheyletiella, demodex). The sarcoptic mange mite can be very difficult to find and several skin scrapings may have to be collected.

Some pets may have more than one medical problem. For example, scratching or biting due to flea irritation can cause a “hot spot” (acute moist dermatitis) and secondary bacterial skin infection (pyoderma) can follow.
Final diagnosis of flea allergy is made based on history, clinical signs and a positive response to flea control.

How can it be treated?

Treatment of flea allergy dermatitis involves three phases:

Prevention of flea bites – The most important part of protection is preventing flea bites with aggressive flea control on the dog and in the environment.
Treatment of secondary skin infections. Antibiotics and antifungal drugs may be necessary to treat secondary skin infections triggered by the flea allergy.
Breaking the itch cycle. If the dog is intensely itchy, a short course of steroids may be necessary to break the itch cycle and make the dog more comfortable.

How can it be prevented?

Use of effective & safe flea control product on the dog on a regular basis beginning one month before the flea season starts and continuing up until one month after the flea season ends.
Use of frequent vacuuming and carpet cleaning strategies to remove eggs and larvae from the dog’s indoor environment. Use of professional cleaning or exterminating service in difficult cases.
Frequent grooming of the dog with a “flea comb” may be helpful to remove fleas.

Attempting to control fleas on our dogs is a multi-step process. There is no successful ectoparasites’ control programme that does not involve treating the environment. To have a successful fleas control programme, one must follow steps to remove fleas from the indoor and the outdoor environment. For the same, usage of insecticidal product as water spray or mopping is suggestive in the pets surroundings also.

(Dr Manish Kawatra, Dr Mandar Deshpande and Dr Vishal Surve of Bayer Pharmaceuticals Pvt Ltd.)