The actual incidence of this group of diseases and their public health importance is not always recognized by the public, public health authorities or the medical profession. Travellers to vector-borne disease endemic areas all too frequently fail to comply with measures of personal protection to prevent contracting an infection such as malaria and often fall ill on their return from travel; frequently diagnosis is delayed as the patient may not have been asked or volunteered information about recent travel or because of a lack of famili– arity with the symptoms of tropical diseases by physicians being consulted. As a result, treatment may also be delayed with serious consequences for the patient. As regards the vector-and rodent-borne diseases endemic to Europe, the USA and Canada, the necessary clinical suspicion to ensure an accurate diagnosis must be based on awareness of distribution of the infections and the risk that travellers may have occurred or the risk that inhabitants of endemic areas face.

Several of this group of vector-and rodent-borne infections have emerged in recent years as diseases of considerable and widespread importance, perhaps foremost among them Lyme disease and West Nile virus. As an example, the incidence of Lyme disease in Germany has risen to an estimated 60 000 cases a year. Overall, Lyme disease has become the most commonly reported arthropod-borne illness in American and European countries.