Résumé
Parasitic organisms in the strict sense (eukaryotes) represent a significant part of the general biodiversity which has been described and, with 179 species affecting people worldwide, are of relevance for mankind in particular. Contrary to the classical view, many of these species are clonal. For example, 72% of human parasites use this means of reproduction. Such parasites represent a major threat to human health. A cumulative inventory leads to an impressive total of 1339 million people being affected by clonal parasites worldwide. These clonal parasites can be classified into different groups depending on how and where asexuality takes place in the life cycle. The demography and population genetics of these groups differ, which is relevant for their treatment. Recent empirical studies have found that the sampling strategy used can dramatically influence how results are interpreted. Furthermore, the role of individual hosts and their gender has been identified as being important for some parasites and that these parasites harbour an unexpected amount of genetic diversity on a very local scale. These issues are discussed in terms of how they may influence the design of therapeutic strategies.