[Human water-contact study on schistosomiasis--its aim, achievement and prospective]

Parasitic helminths can not choose a strategy for fighting against their hosts but can only compromise with them. They do not kill their hosts because the host is necessary for their survival. Schistosoma haematobium, one of the main causes of tropical parasitic diseases, is a parasitic helminth whose only host is human beings and therefore is considered to evolve fully while adapting to humans. In a human community, the peak intensity and peak prevalence of S. haematobium infection occur in adolescence and suddenly decline thereafter. This is advantageous for the hosts and could be explained as a typical strategy of parasitic helminths. The possible mechanisms of maintaining this host-parasite relationship are the development of acquired protective immunity and the change of human water-contact behavior by age. However, our study in Kenya indicates that the worm burden is regulated mainly by the change of human water-contact behavior. Since human behavior depends on the cultural background of the society, the relation between humans and S. haematobium is an example of the great influence that the human culture has on the host-parasite relationship. For any further investigation of tropical infectious diseases, socio-cultural research is indispensable.