Travellers from the northern hemisphere are not always aware of the danger of contracting diseases while in the tropics, nor are they necessarily aware that if they are ill within a year of their return home, they should tell their doctor that they have been to the tropics, so that the doctor knows to consider tropical diseases among the possible causes.
2000 people a year return to the UK with malaria, of whom 10 die. Patients who die have usually waited too long for treatment. Bilharzia is on the rise among returning travellers, and skin rashes and dog hookworm turn up in Caribbean tourists. 79% of heterosexually transmitted HIV cases in the UK are acquired abroad.