Endemic parasitic diseases surely make the largest and most original part in the scope of tropical medicine. A hot and humid climate is often an ideal environment for the survival of both parasites and their eggs and it also makes possible the development of a multitude of vector insects. In the tropics, standards of sanitation are usually very low as water is often in short supply and is often unsafe.

Penetration of parasites occurs either directly through the digestive tract or in a few other instances through the skin. These are the means of transmission for all parasitic diseases of the digestive tract and especially for amoebiasis which is a dreadful condition. They are often conveyed by water which is either ground water or streaming down water as the faecal risk is widespread. The pathogen of bilharziosis, among others, penetrates through the skin.

Biting or sucking insects are even more harmful as, upon feeding on a healthy individual’s blood they regurgitate parasites which they have taken from a sickened one, on the occasion of their previous meal. In order to achieve their cycle of development most of these insects need water, either stagnant water such as for the vectors of malaria and trypanosomiasis or running water such as for onchocerciasis.