Dog - Flea Allergy Dermatitis

I have always had an itchy dog and every summer he has had to have treatment.  Recently he underwent a lot of tests and I have been told that he has flea allergy dermatitis.  I have never seen a flea on him.

Dogs can be irritated by fleas in two ways:

1. A very small percentage of dogs are irritated by the presence of fleas on the skin and also the irritation from their physical bites.
2. Flea allergy dermatitis (FAD).  This is the most common disorder encountered in small animal dermatology.  Fleas do not live on the dog for the whole of their lives but they do need a blood meal in order to complete their life cycle.  When they bite to feed they inject a tiny amount of saliva into the skin and in susceptible individuals it is this substance which results in the allergic reaction.  It causes intense itching and often extensive sore areas due to persistent scratching and biting.

Are only certain dogs allergic to fleas?

FAD can affect virtually any dog although some appear to be more prone than others.

Is it affected by the weather?

It may be seasonal.  Many cases appear to start in late summer and early autumn when weather conditions favour rapid flea reproduction but it can occur at any time of the year.

I have never found a flea on my dog.

This is a common comment from owners.  Fleas do not have to live on the dog but only need to bite the dog to secure the all essential blood meal.  If your dog does have a flea hypersensitivity this is sufficient to trigger the irritation.  Your dog will then scratch and the resulting soreness when healing will cause more irritation and thus the condition carries on.

I have no other pets, how can my dog pick up fleas?   I try to carry out all your instructions regarding the application of flea preparations.

Fleas only live for a small portion of their lives on the animal (mainly to feed).  The rest of the time they will live in the environment and this can be outside if climatic conditions are suitable.  Recent warm and humid summers have led to an increase in fleas and thus your dog can easily pick up a flea, or fleas, when out at exercise.  Also if he comes in contact with other dogs or cats the occasional flea may be transferred.

How is flea allergy dermatitis diagnosed?

Careful flea control has always been an essential part of the diagnosis.  Today we have very effective preparations, not only for use on the dog but also for use in the environment and some of these will eliminate not only fleas but the larvae as well.  In addition, certain laboratory tests can be carried out but these are usually only confirmatory when positive since false negatives are common.

Fleas are particularly prevalent in warm, humid conditions when new populations are hatching every 14-21 days.  All of these will need a blood meal in order to produce the next generation.  Every one of these fleas poses a potential risk for any dog suffering from FAD.

Control becomes a problem for those dogs that live mainly outside since in hot humid conditions the environment cannot be controlled as rigorously as in the home.

If you have problems please feel free to consult us.

What does treatment involve?

It is the injection of flea saliva that causes the allergic response therefore this must be prevented.  Strict flea control is essential.  Even though you have not seen fleas on the dog it is important that you continue rigorous flea treatment of the animal and also maintain environmental flea prevention.   See handout on Flea control.

Dogs which live outdoors pose a particular challenge since if the weather is warm and humid, new populations of fleas are hatching in the environment every 14-21 days.  Please feel free to discuss this with us.

What about desensitisation?  I understand that this is an alternative approach.

In certain circumstances desensitisation techniques are worthwhile.  Densitisation involves injecting increasing doses of a special flea antigen (vaccine) over a prolonged period of time.  However this line of approach is only successful in approximately 50% of cases.  Frequent booster doses are also required.

Are there any other lines of treatment?

Other lines of treatment aimed to suppress the irritation and thus improve the dog's quality of life are available.   We will be happy to discuss the options with you but emphasise that strict flea control, both in the environment (home) and on the dog is by far the most effective method of controlling the problem at present.

What about cortisone?

Cortisone, corticosteroids, or steroids are used very widely for the symptomatic treatment of FAD.  Such preparations are invaluable for short term use in the very itchy dog but they do have serious side effects if their use is prolonged.

Today vigorous flea control is still the most effective and safest method of treatment.

Please contact us to discuss this further.