Directly and indirectly the flea is probably the cause of more dermatological disorders in small animals than all other etiological agents together (Keep 1983).

Concerning the pathogenic effect of flea infestation, differentiations between the direct consequences of a flea bite, the allergic reactions of the host and the effect of blood consumption by the fleas have to be made (Kalvelage and Münster 1991).

On the one hand there is flea bite dermatitis and on the other hand there is flea bite hypersensitivity which according to Halliwell (1985a) can also be defined as flea allergy dermatitis (FAD). Newer research and diagnostic techniques suggest that most of the cases of dermatitis without the presence of allergic hypersensitivity reaction do have hypersensitivities and that dermatitis without allergy is a rare phenomenon (Halliwell 1983, 1986). Nevertheless several authors still differ between the two clinical situations of flea bite dermatitis and flea bite hypersensitivity (FAD).

Once the flea has found a host for the uptake of blood a few test bites have to be performed until a blood leading capillary vessel has been found (Karandikar and Munshi 1950). The direct contact with the host’s skin as well as these bites cause an irritation of the skin, pruritus and an insignificant, transient invasion of lymphocytes in the direct proximity of the biting site (Gothe 1985). These local reactions are suggested to be principally similar in all hosts, whereas in the so far examined animal species differences exist concerning allergic reactions (Kalvelage and Münster 1991).