Motility precedes egress of malaria parasites from oocysts.

Dennis Klug,Friedrich Frischknecht

doi:10.7554/elife.19157

Abstract

Malaria is transmitted when an infected Anopheles mosquito deposits Plasmodium sporozoites in the skin during a bite. Sporozoites are formed within oocysts at the mosquito midgut wall and are released into the hemolymph, from where they invade the salivary glands and are subsequently transmitted to the vertebrate host. We found that a thrombospondin-repeat containing sporozoite-specific protein named thrombospondin-releated protein 1 (TRP1) is important for oocyst egress and salivary gland invasion, and hence for the transmission of malaria. We imaged the release of sporozoites from oocysts in situ, which was preceded by active motility. Parasites lacking TRP1 failed to migrate within oocysts and did not egress, suggesting that TRP1 is a vital component of the events that precede intra-oocyst motility and subsequently sporozoite egress and salivary gland invasion.

Highlights

Many parasites switch between multiple hosts in order to complete their life cycles
thrombospondin-releated protein 1 (TRP1) belongs to the family of thrombospondin-related anonymous protein (TRAP)-related proteins
Plasmodium sporozoites display a repertoire of proteins that are important for egress from oocysts (SERA5, CSP, GAMA, sporozoite invasion associated protein-1 (SIAP-1), PCRMP3 and 4, and CCp2 and 3), motility (e.g. TRAP, MAEBL and S6) and salivary gland entry (e.g. TRAP and MAEBL)

Summary

Introduction

Many parasites switch between multiple hosts in order to complete their life cycles. These host switches are often accompanied by population bottlenecks where just a few parasites are sufficient for infection. For Plasmodium, the causative agent of malaria, a host switch is followed by an expansion of the parasite population in both the insect and the vertebrate host. A single Plasmodium parasite that establishes itself in the mosquito gut is enough to form an extracellular oocyst, in which hundreds of sporozoites can develop to colonize the salivary gland and be injected back into the vertebrate host. In order to progress to the developmental stage, the fully formed parasites need to escape their respective host cell or the oocyst

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Conclusion