![]() ![]() Once the mature stage V gametocytes are ingested with the blood meal of an Anopheles mosquito, they are activated in the mosquito midgut by environmental stimuli, and gametogenesis is initiated (Fig. falciparum, during which they pass five morphological stages, termed stages I–V. A time period of about 10 days is required for gametocyte development in P. ![]() Sexual precursor cells, the intraerythrocytic gametocytes, develop in the human blood in response to stress factors (reviewed in Pradel, 2007 Kuehn and Pradel, 2010). A fourth aspect deals with the interplay between parasites and midgut factors, including the gut microbiota and epithelium, components of the human blood meal and insect immune molecules. In this context, three consequent steps are considered, the signalling cascade leading to gametogenesis, the formation of gametes and the zygote‐to‐ookinete conversion. ![]() This review summarizes the recent findings on the mosquito midgut stages of Plasmodium. Two models were used in the majority of these studies, the rodent malaria parasite Plasmodium berghei and the in vitro cultivable human parasite Plasmodium falciparum. Boosted by technical advances in parasite genetics and live‐cell imaging and complemented with data gained by transcriptomics and proteomics, in recent years, novel insights into the mosquito midgut phase of the malaria parasite were obtained. The plasmodial midgut stages are attractive objects to study a variety of cell biological aspects, including cell conversion, signal perception, parasite/host co‐adaptation and immune evasion. This replication phase requires roughly 2 weeks and results in the formation of infective sporozoites that migrate to the salivary glands to be released into the human dermis with the next bite of the mosquito, wherewith the life‐cycle of Plasmodium is completed (reviewed in Aly et al., 2009 Ghosh and Jacobs‐Lorena, 2009 Kuehn and Pradel, 2010 Ménard et al., 2013). Subsequently, the ookinetes settle down at the basal site of the midgut epithelium and convert to sessile oocysts, in which sporogonic replication takes place. The midgut phase lasts for approximately 20 h and includes two phases of stage conversion, the rapid conversion of gametocytes into fertile gametes upon activation and the conversion of zygotes into the motile and invasive ookinetes that once formed, immediately exit the gut lumen by traversing the midgut epithelial cell layer. In the mosquito midgut, the parasites are able to differentiate into their sexual forms, the female macrogametes and male microgametes, and to then undergo sexual reproduction in order to newly combine their chromosomal sets. These blood infections can last for months, and only once sexual precursor cells, the gametocytes, have matured, the malaria parasites are able to leave the human host and to continue the life‐cycle in the insect vector. Once transmitted to the human by a blood‐feeding female Anopheles mosquito, the parasites initially multiply in the human liver, before they progress to the pathologic blood stages. Children are particularly susceptible to malaria, and in 2015, an estimated 306 000 children under 5 years of age were killed, mostly in the African region (WHO World Malaria Report, 2015). Malaria, a vector‐borne blood disease caused by protozoan parasites of the genus Plasmodium, results in 214 million infections and claims 438 000 deaths every year. This review highlights recent insights into the molecules involved in gametocyte activation and gamete formation as well as in zygote‐to‐ookinete conversion and ookinete midgut exit it further discusses factors that can harm the extracellular midgut stages as well as the measures of the parasites to protect themselves from any damage. The mosquito midgut stages of malaria parasites are unprecedented objects to study a variety of cell biological aspects, including signal perception, cell conversion, parasite/host co‐adaptation and immune evasion. Further, gamete formation requires parasite egress from the enveloping erythrocytes, rendering them vulnerable to the aggressive factors of the insect gut, like components of the human blood meal. During this time period, the plasmodia undergo two processes of stage conversion, from gametocytes to gametes and from zygotes to ookinetes, both accompanied by dramatic morphological changes. Parasite development in the midgut starts with the activation of the intraerythrocytic gametocytes immediately after take‐up and ends with traversal of the midgut epithelium by the invasive ookinetes less than 24 h later. The mosquito midgut stages of malaria parasites are crucial for establishing an infection in the insect vector and to thus ensure further spread of the pathogen. ![]()
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