Page 124 - 80 guidelines for the treatment of malaria_opt

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Guidelines for the treatment of malaria – 2 edition

Figure A4.1 relationship between inoculation rate and parasite prevalence
(assumes that all infections are untreated)

100
80
% parasite prevalence 60

40

20
0
0.1 1 10 100 1000
Annual entomological inoculation rate

a4.2 effect of medicines on malaria transmission

Medicines can lead to reducing malaria transmission by two mechanisms (4).
1. Early and effective treatment of a malaria blood infection with any antimalarial will
reduce gametocytes by eliminating the asexual blood stages from which gametocytes
derive. The faster the clearance of asexual blood parasites the greater the effect on
reducing infectivity. The potent anti-infective properties of artemisinins are, therefore,
partly due to their rapid parasite clearance action. In P. vivax, P. malariae and P. ovale,
gametocytes have a short developmental period (2–3 days) and mature gametocytes
are short-lived. Therefore, effective treatment of the asexual blood infection alone will
be sufficient to abolish infectivity to mosquitoes. In P. falciparum, gametocytes take
longer to develop (about 12 days) and mature from a young parasite (merozoite). In
the peripheral circulation, mature gametocytes may remain infective for up to several
weeks. Hence, infectivity of a P. falciparum infection could remain for weeks after the
patient has been successfully treated unless a specific anti-gametoycte medication (e.g.
primaquine, see below) has been used.
2. By lowering parasite infectivity through either a direct effect on gametocytes
(gametocytocidal effect) or on the parasite developmental stages in the mosquito
(sporonticidal effect) (Table A4.1; Fig. A4.2). Chloroquine, widely used to treat
P. falciparum disease (asexual blood parasites) in the past, acts against young
gametocytes, but it has no suppressive effect on (5) the infectivity of mature infective
gametocytes (6), and may even enhance it. In contrast, sulfadoxine-pyrimethamine
increases gametocyte carriage but reduces their infectivity (6–8). Artemisinins are
the most potent gametocytocidal drugs among those currently being used to treat
an asexual blood infection (9–13). They destroy young gametocytes, preventing new
infective gametocytes from entering the circulation, but they have less effect on mature
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