**8. Merozoites**

The budding of the merozoites from interconnected cytoplasmic masses (pseudocytomeres) is a complex process. At the tip of each bud a thickened region of pellicle gives rise to the apical rings and conoid. As development proceeds an aggregation of smooth membranes and the nucleus enter the base of the bud. The cytoplasm contains numerous large ribosomes. synchronous multiple cytoplasmic cleavage of the mature schizont results in the formation of numerous uninucleate merozoites.

Escape of the merozoites from the erythrocyte has also been studies. The erythrocyte swells under osmotic pressure. A pore opens in the erythrocyte membrane and 1-2 meorozites

Biology of Malaria Parasites 15

membrane are recognizable. The nuclei are recognizably dimorphic into male and female.

In stage two gametocytes becomes D shaped. The nucleus may occupy a terminal end of the cell or lie along its length. Early spindle formation may be visible. These forms are found

In stage three the erythrocyte becomes distorted. A staining difference between the male and female gametocytes is apparent (male stain pink while female stain faint blue with the usual stains). The male nucleus is noticeably larger than the female and more lobulated. The

In stage four erythrocytes is clearly deformed and the gametocyte is elongated. The male gametocytes stain red while the female stain violet blue. In the male pigment granules are scattered while in the female they are denser. In the male the kinetochores of each chromosomes are located over a nuclear pore. Osmophilic bodies are found in both but are more numerous in the female. These forms are found between day 6 and day 10 in *P* 

In stage five the gametocytes are clearly recognizable on light microscopy with the typical banana shaped female gametocytes. The subpellicular microtubules depolymerise but the membrane itself remains. The male gametocyte exhibit a dramatic reduction in ribosomal density. Very few mitochondria are retained and the nucleus enlarges with a kinetochore complex attached to the nuclear envelope. In the female gametocytes there are numerous mitochondria, ribosome's and osmophillic bodies. The nucleus is small with a transcription

Stages other than five are not normally found in the peripheral blood. For reasons not yet understood stage 1 to IV are sequestered preferentially in the bone marrow and spleen. Stage V gametocytes only become infections to mosquito's after a further two days of

In the mosquito's midgut, the gametocytes develop into gametes and fertilize each other, forming motile zygotes called ookinetes. It has been shown that up to 50% of the ookinetes may undergo apoptosis within the mighut. The reason for this behavior is unknown. While in the mosquito gut the parasites form thin cytoplasmic extensions to communicate with each other. These structures persist from the time of gametocyte activation until the zygote transforms into an ookinete. The function of these tubular structures remains to be

The ookinetes penetrate and escape the midgut, then embed themselves onto the exterior of the gut membrane. As in the liver the parasite tends to invade a number of cells before choosing one to reside in. the reason for the behavior is not known. Here they divide many times to produce large number of tiny elongated sporozoites. These sporozoites migrate to the salivary glands of the mosquito where they are injected into the blood and subcutaneous

female cytoplasm has more ribosomes, endoplasmic reticulum and mitochondria.

These forms may be found between 0 and 2 in *P falciprum* infections*.*

between days 1 to day 4 in *P falciprum* infections.

*falciparum* infections.

factory.

circulation.

discovered.[20]

**11. Infection of mosquito** 

tissue of the next host the mosquito bites.

escape. This is followed by an eversion of the entire erythrocyte membrane. An action that propels the merozoites into the blood stream.

Invasion of erythrocyte precursors has only recently been studied. The earliest stage susceptible to infection were the erythroblasts – the stage immediately preceding the reticulocyte stage which in turn is the immediate precursor to the mature erythrocyte. Invasion of the erythrocyte is inhibited by angiotensin 2. This is normally metabolized by erythrocytes to angiotensin (Ang) IV and Ang – (1-7). Parasite infection decreased the Ang – (1-7) levels and completely abolished Ang IV formation. Ang – (1-7), like its parent molecule, is capable of decreasing the level of infection. The mechanism of inhibition seems likely to be an inhibition of protein Kinase A activity within the erythrocyte.
