Malaria is a major global health problem, with an estimated 300 to 500 million clinical cases occurring annually. Malaria remains one of the leading causes of disease and death in the tropics, mainly of children under 5 years of age. The most prevalent and dangerous type of malaria is caused by Plasmodium falciparum. P. vivax is a common cause of malaria in Latin America, Asia, and Oceania, but not Africa. P. malariae and P. ovale are much less common. Antimalarials are used in three different ways: prophylaxis, treatment of falciparum malaria, and treatment of non-falciparum malaria. Prophylactic antimalarials are used almost exclusively by travelers from developed countries who are visiting malaria-endemic countries. The antimalarials in common use come from the following classes of compounds: the quinolines (chloroquine, quinine, mefloquine, amodiaquine, primaquine), the antifolates (pyrimethamine, proguanil and sulfadoxine), the artemisinin derivatives (artemisinin, artesunate, artemether, arteether) and hydroxynaphthaquinones (atovaquine).

Planarians can reproduce exclusively sexually or/and asexually by fissiparity. Among fissiparous populations individuals can sexualize and develop ovaries of remarkable size called hyperplasic ovaries (Gremigni and Banchetti, 1972). Nevertheless, it has been reported that individuals that become sexual are usually sterile because they usually lay infertile cocoons (Grasso and Beanzzi, 1973).The aim of this study is to demonstrate, through ultrastructural and TdT‐mediated dUTP nick end‐labeling (TUNEL assay) in intact sections of hyperplasic ovaries the cause of infertility of ex‐fissiparous planarians. Our study has been carried out on Dugesia arabica collected from Yemen (Harrath et al., 2013) that reproduce asexually in the field. After having been kept for few months in the laboratory, some of the specimens had been sexualized.Ultratsructural and TUNEL assay investigations demonstrate that oogonia and young oocytes still develop normally compared to previous studies describing oogenesis in other Dugesia species. At the later stage, very few fertile oocytes of a hyperplasic ovary may succeed in completing their growth whereas the majority at the diplotene stage undergoes a progressive degeneration through programmed cell death. The latter leads to the self‐destruction of oocytes and may represent the most important cause of infertility of ex‐fissiparous planarians. This process should be correlated with polyploidization or genomic variations.