Biology Reference
In-Depth Information
Fig. 19.3 a Cartoon of Plasmodium life cycle. The parasite replicates within erythrocytes
through schizogony. Some differentiate into sexual stages that are transmitted to the mosquito
during a blood meal, generating a motile egg cell that transverses the mosquito midgut, forming a
cyst. Within the cyst, the parasite replicates through schizogony, forming the infective stages that
are transmitted back to the host. These forms enter the blood circulation, ending up in
hepatocytes, where they again multiply, generating thousands of parasites that will ultimately
enter the erythrocytes. The numbers indicate the different stages of the cycle where the division
process occurs: inside the cyst in the mosquito (1), in the hepatocyte (2), and within the red-blood
cell (3). b and c Morphological modifications occur in the apicoplast and mitochondrion during
schizogony. Here are fluorescence light microscopy images of a Plasmodium strain expressing an
mitochondrion molecule tagged with GFP (in green) and a apicoplast protein tagged with DsRed
(in red) during the division process inside an erythrocyte (After van Dooren et al.
2005
; with
permissions of the John Wiley and Sons)
parasites. This rapid division process where cell division is uncoupled from
genome replication is called schizogony (Striepen et al.
2007
; Gerald et al.
2011
).
Once the parasites are released into the bloodstream, they invade erythrocytes,
again forming a PV. Inside the PV, the parasites replicate generating ca. 20
progeny per cell, which can infect new erythrocytes. While this cycle can go on
until most of the red blood cells in the body are consumed, some parasites can
form two different sexual stages. When those are picked up by a subsequent
mosquito bite, the flagellated male gamete fertilizes the female gamete, forms a
zygote and subsequently a diploid motile egg cell that exits from the mosquito
stomach, crossing the surrounding epithelial cell layer to form a cyst. In this cyst,
again, the parasite undergoes schizogony to generate the forms that are ultimately
transmitted back to the host.
