Page 126 - 80 guidelines for the treatment of malaria_opt

nd
Guidelines for the treatment of malaria – 2 edition

Figure A4.2 Transmission of and the effects
of antimalarials

ANTIMALARIAL DRUGS PARASITE DEVELOPMENT
AND THEIR EFFECTS* Some will re-enter
erythrocytes and develop
into schizonts (asexual cycle)
Chloroquine
when sensitive
Amodiaquine Treatment of the asexual blood
–
Sulfadoxine- infection will abolish the source
pyrimethamine of the gametocytes.
Artemisinin-
derivatives when resistant
+ SCHIZONT MEROZOITES
Some will re-enter erythrocytes and
develop into gametocytes However, young gametocytes
in already present will continue to
mature and become infective
human weeks later.
Artemisinin- – blood YOUNG GAMETOCYTE Artemisinin derivatives and, to a
derivatives SEQUESTERED IN TISSUES
far lesser extent, chloroquine will
act against young gametocytes,
and thereby reduce the number
of mature infective gametocytes.
8–10 days
MATURE GAMETOCYTE IN
– PERIPHERAL CIRCULATION, Primaquine is the only drug
Primaquine REMAIN INFECTIVE TO known to act on mature
MOSQUITOES FOR 10-14 DAYS gametocytes (which are present
in the circulation at the time the
patient presents for treatment).
The parasite undergoes
– fertilization and further
Sulfadoxine- in the
pyrimethamine mosquito development in the midgut, and
+ the salivary glands of the
mosquito.
Chloroquine
*When parasites are sensitive to the drug unless otherwise stated. Positive and negative arrows
indicate the effect of the drug, enhancement (+) and suppression (–), respectively, on the parasite
stage or its development.
a4.2.2 in situations of intense transmission
In high-transmission settings, infected but asymptomatic persons constitute an important
part of the infectious reservoir. Even though treated cases (mainly children) have higher
densities of gametocytes, and infectivity is positively related to gametocyte density,
children constitute only a proportion of the infective reservoir (15). This, together with
the fact that, in high transmission settings, a considerable reduction in transmission
rates is needed to impact on parasite prevalence (and incidence of disease), makes a less
compelling case for introducing an infectivity-suppressing component into the treatment
schedule. However, as malaria control efforts intensify in highly endemic countries,
transmission rates are declining and infectivity-reducing drug regimes will have a useful
role to play in sustaining those achievements. The use of antimalarial drugs to reduce
infectivity:

• is justified in low-transmission settings;
• will be beneficial in high-transmission settings when transmission rates have been
lowered by effective malaria control.
112