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.  Flea dermatitis. A very small percentage of dogs will be caused irritation by the presence of fleas on the skin and also irritation from their physical bites.

2.  Flea allergy dermatitis (FAD). This is the most common disorder encountered in small animal medicine. 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 minute amount of saliva into the skin and in susceptible individuals it is this substance which results in the allergic reaction causing intense itching and often extensive sore areas solely due to persistent scratching and biting.

Are only certain dogs allergic to fleas?

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

It may be seasonal. Many cases appear to start in spring and summer when weather conditions favour rapid flea reproduction but it can occur at any time of the year especially in the more tropical regions of Australia.

But 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? Besides, I strictly carry out the vet’s 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 more 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?

In the past this was frequently by elimination, mainly elimination of the fleas but also elimination of other possible causes of the itching. Careful flea control was an essential part of the diagnosis. Today we can also use skin and sometimes blood tests which will detect animals that have a specific flea allergy.

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. A separate handout outlines the procedures. 

"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."

Dogs which live outdoors pose a particular challenge since if the weather is warm and humid, new populations of fleas are hatching every 14-21 days, all of which need to have a blood meal in order to produce the next generation. All are a potential risk to any dog suffering from FAD.

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

Desensitisation involves injecting increasing doses of a special flea antigen (vaccine) over a prolonged period of time. Frequent booster doses are also required. This line of approach is only successful in approximately 50% of cases. However in certain circumstances desensitisation techniques are worthwhile. In addition, there are other lines of treatment aimed to suppress the irritation and thus improve the dog’s quality of life. These we will discuss with you in respect to effectiveness, cost etc.

Do you mean steroid treatment?

Corticosteroids, “cortisone” or “steroids” are used very widely for the treatment of FAD. Their use often brings about miraculous relief for the poor itchy patient. There are significant side effects but these can be minimized through careful use and maintaining the lowest doses possible. Corticosteroids are best reserved for short term use and the long term use of steroids is usually reserved for especially severe cases where all other options have been explored. Indiscriminate use of corticosteroids may result ultimately in doing more harm than good. Apoquel (oclacitinib) can also be useful as alt to cortisone.