Models of Acquired Immunity to Malaria: A Review

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Figure 5.1: Malaria life cycle [107].

of the mosquito to form an oocyst, within which thousands of sporozoites develop. The

sporozoites are moved to the salivary glands of the mosquito. Upon biting the human,

the sporozoite-stage parasites contained in their salivary gland are injected into the human

bloodstream from where they are transferred to the liver cells. At this stage, each sporozoite

multiplies inside a hepatocyte and develops into thousands of schizonts, which rupture and

give birth to merozoites that are thereafter released into the blood stream. The release of

merozoites into the blood initiates the erythrocyte stages, (often referred to as asexual blood

stages) where they invade and replicate within red blood cells (RBCs) causing the infected

person to experience malaria symptoms. On the other hand, some of the asexual blood

parasites (merozoites) can develop into gametocytes which mosquito ingests upon biting,

resulting into parasite transmission to the mosquito; and the cycle continues. Thus, asexual

parasites are responsible for illness, whereas gametocytes are responsible for transmission

from human to vector [25] (see Figure 5.1 for more visual details).

Naturally acquired immunity usually occur when an individual is exposed to a live

pathogen which as a result, brings about the creation of antibodies by the immune system

[216]. According to [36], upon recovery from reinfection, there is usually rapid boosting

of antibody responses to various antigens, as an indicator of the presence of memory B

cells. It can take some days or weeks for the adaptive immune response generated against

the pathogen to develop but may be long-lasting, or even lifelong. For example, infec-

tion with chickenpox or measles infection and subsequent recovery, gives rise to a natural