Transmission stages of Plasmodium: does the parasite use the one same signal, provided both by the host and the vector, for gametocytogenesis and sporozoite maturation?
Among the microorganisms that strictly depend upon other organisms (hosts or vectors) for achieving their life cycle, protozoan and metazoan parasites have been often primarily distinguished through the major pathogenic processes they could induce. A variety of different mechanisms linked to parasitism can indeed systemically (e.g. Plasmodium falciparum) or locally (e.g. Toxoplasma gondii) induce important alterations of tissue homeostasis. But more than obvious pathogenicity, it is the capacity to be transmitted that is essential for parasite survival and there is increasing evidence that certain parasites can achieve their life cycle to the point of transmission in the absence of clinically detectable processes. For this, constitutive microenvironments of the host or vector can be exploited. Moreover, parasites are sometimes able to highjack effectors of the host's immune response towards conditioning the microenvironments which are permissive to differentiation of transmissible developmental stages. Based on a few examples taken from studies on the transmission stages of Leishmania, Toxoplasma and Plasmodium, we have here attempted to formulate a few hypothesis on the biology of the transmission stages of P. falciparum, i.e. on gametocytogenesis and sporozoite maturation. As discussants, we may have been somewhat dwarfed by issues evoked by the organizers of this meeting in the title of the session, i.e. 'Vector-parasite-man interactions'!... In reaction, we may have taken refuge in somewhat over-selective comments, biased by the objects of our personal research....
Milon
G
G
Unité d'Immunophysiologie et Parasitisme intracellulaire, URA CNRS 1960, Institut Pasteur, Paris, France. gmilon@pasteur.fr
David
P H
PH
D000818:Animals; D005260:Female; D005854:Germ Cells / Q000254:growth & development; D006790:Host-Parasite Interactions; D006801:Humans; D007303:Insect Vectors; D016778:Malaria, Falciparum / Q000635:transmission*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism; D010963:Plasmodium falciparum / Q000472:pathogenicity*; D012733:Sex Differentiation
D009569:Nitric Oxide