Page 197 - Concise Pathology for Exam Preparation ( PDFDrive )

182 SECTION I General Pathology

Life Cycle (Flowchart 7.4)

Sporozoites reach blood by bite of an infected
mosquito (female Anopheles)

They invade and attach to liver cells (binding to hepatocytic
receptors for proteins thrombospondin and properdin)

Multiply asexually in the liver cells Hepatic phase

Merozoites (asexual haploid forms) released
into circulation when hepatocytes rupture

Bind to RBCs via lectin on glycophorin molecules
of RBC membrane (P. vivax binds to Duffy Ag)

Merozoites release proteases from a special
organelle called Rhoptry Erythrocytic phase

Multiply in RBCs, within which parasites grow in
membrane-bound digestive vacuoles and hydrolyse
haemoglobin via serotonin enzymes, converting haem to haemozoin

Note: First stage of parasite in RBCs is ring stage, followed by trophozoite and schizont
form (Figure 7.15).
Some merozoites develop into sexual forms called gametocytes that infect mosquito when it takes a blood meal

Once ingested, the parasite gametocytes taken up in the blood will further differentiate into male or
female gametes
(Fig. 7.16) and then fuse in the mosquito gut

This produces an ookinete that penetrates the gut lining and produces an oocyst in gut wall

When the oocyst ruptures, it releases sporozoites that migrate through the mosquito’s body to its salivary
glands, where they are then ready to infect a new human host
FLOWCHART 7.4. Lifecycle of malarial parasite.

Shizoint

FIGURE 7.15. Schizont form of malarial parasite.

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