Malaria

Life Cycle

Hypnozoites are a quiescent stage in the liver that exist only in the setting of P. vivax and P. ovale infection.

This liver stage does not cause clinical symptoms, but with reactivation and release into the circulation, late-onset or relapsed disease can occur up to many months after initial infection.

Primaquine is active against the quiescent hypnozoites of P. vivax and P. ovale

The schizonts rupture and release merozoites into the circulation where they invade red blood cells. Within red cells, merozoites mature from ring forms to trophozoites to multinucleated schizonts (erythrocytic stage).

Blood-stage schizonticides such as artemisinins, atovaquone-proguanil, doxycycline, mefloquine, and chloroquine interrupt schizogony within red cells.

Primaquine is a blood-stage schizonticide with activity against schizonts of P. vivax but not those of P. falciparum.

Tissue (hepatic) schizonticides – These drugs target the liver stages of the parasite, the active tissue schizonts. Atovaquone/proguanil has proven activity against liver stages of P. falciparum.

Dx

Blood smear (thin & thick):

Trophozoite ring form within RBC

Schizont containing merozoites;

Red granules (Schuffner stippling) throughout RBC cytoplasm seen with P vivax/ovale)

Treatment

This patient has uncomplicated falciparum malaria, with a low level of parasitaemia at 1%. As such, an oral artemesin preparation, such as artemether and lumefantrine combination tablets, is indicated. Both components act at the level of the food vacuole of the malarial parasite where they are thought to interfere with the conversion of haem, a toxic intermediate produced during haemoglobin breakdown, to non-toxic haemozoin. Lumefantrine is thought to interfere with the polymerisation process. Artemether generates reactive metabolites as a result of the interaction between its peroxide bridge and haem iron. Both artemether and lumefantrine have a secondary action involving inhibition of nucleic acid and protein synthesis within the malarial parasite.

One tablet contains 20 mg artemether and 120 mg lumefantrine. In adults, a course of therapy is 24 tablets given over a period of 60 hours.

Intravenous artesunate