Plasmodium gallinaceum: density dependent limits on infectivity to Aedes aegypti

Spatial distribution of factors that determine sporogonic development of malaria parasites in mosquitoes

Mosquitoes transmit malaria, but only a few species permit the complete development and transmission of the parasite. Also, only a fraction of the ingested parasites develop in the vector. The attrition occurs in different compartments during the parasite's complex developmental scheme in the insect. A number of factors, both physical and biochemical, that affect the development have been proposed or demonstrated. Each of these factors is located within a specific space in the insect. We have divided this space into six compartments, which are distinct in their biochemical and biophysical nature: Endoperitrophic space, Peritrophic matrix, Ectopretrophic space, Midgut epithelium, Haemocoel and Salivary gland. Because factors that influence a particular stage of parasite development share the same microenvironment within these compartments, they must be considered collectively to exploit them for designing effective transmission blocking strategies. In this article we discuss these factors according to their spatial location in the mosquito.

Malaria parasite development in mosquitoes

Mosquitoes of the genus Anopheles transmit malaria parasites to humans. Anopheles mosquito species vary in their vector potential because of environmental conditions and factors affecting their abundance, blood-feeding behavior, survival, and ability to support malaria parasite development. In the complex life cycle of the parasite in female mosquitoes, a process termed sporogony, mosquitoes acquire gametocyte-stage parasites from blood-feeding on an infected host. The parasites carry out fertilization in the midgut, transform to ookinetes, then oocysts, which produce sporozoites. Sporozoites invade the salivary glands and are transmitted when the mosquito feeds on another host. Most individual mosquitoes that ingest gametocytes do not support development to the sporozoite stage. Bottle-necks occur at every stage of the cycle in the mosquito. Powerful new techniques and approaches exist for evaluating malaria parasite development and for identifying mechanisms regulating malaria parasite-vector interactions. This review focuses on those interactions that are important for the development of new approaches for evaluating and blocking transmission in nature.

The biology of malarial parasite in the mosquito--a review

The purpose of this review is to summarize the biology of Plasmodium in the mosquito including recent data to contribute to better understanding of the developmental interaction between mosquito and malarial parasite. The entire sporogonic cycle is discussed taking into consideration different parasite/vector interactions and factors affecting parasite development to the mosquito.

The establishment of Plasmodium berghei in mosquitoes of a refractory and a susceptible line of Anopheles atroparvus

The events between the ingestion of Plasmodium berghei-infected mouse blood and the establishment of the ookinetes in the epithelium of the midgut in refractory (R) and susceptible (S) Anopheles atroparvus are described. Simultaneously fed, fully engorged female mosquitoes were randomly assigned to dissection at 22, 28, 32, 48 h and 10 days (controls) after the infective feed (post-infection: p.i.). Serial transverse sections of 6 micron were cut. Every 10th section was studied. The maturation of ookinetes was monitored at 16, 19 and 22 h p.i. The infections in R and S mosquitoes developed similarly with regard to the maturation of ookinetes and the number of mature ookinetes in the lumen of the midgut. The semiquantitative evaluation of the envelopment of the food bolus by the peritrophic layer showed that this layer cannot function as a physical barrier against migrating ookinetes. In the midgut epithelium the number of ookinetes decreased significantly with time in both R and S mosquitoes, but a similar number of penetrations was recorded for both types of mosquito. In S mosquitoes maximal 1% of the ookinetes present in the midgut formed an oocyst. In both R and S mosquitoes a substantial loss of parasites was found, first in the lumen of the midgut and second after penetration of the midgut epithelium by the mature ookinetes. Relatively few parasites develop into oocysts in S, but hardly any do so in R individuals. The factors in control of refractoriness are likely to operate on early oocyst development.

Development of Plasmodium berghei ookinetes in the midgut of Anopheles atroparvus mosquitoes and in vitro

Plasmodium berghei ookinete formation in vitro and within the midgut of susceptible Anopheles atroparvus were compared. No significant morphological differences were seen, except that in vitro development was more synchronized and less degenerating forms occurred. In vitro ookinete yields were 4-31 times higher and less variable than those in vivo. Mosquitoes of a susceptible and of a refractory line of A. atroparvus were simultaneously fed on the same host or via a membrane with the same suspension of in vitro-formed mature ookinetes. Up to 100% of mosquitoes of the susceptible line produced oocysts, mostly in high numbers, whereas infection rates and numbers of oocysts produced in mosquitoes of the refractory line were lower and much more so after host feeding than after membrane feeding of mature ookinetes, indicating that refractoriness does not depend on a single process of inhibition.