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Guidelines for the treatment of malaria – 2 edition

ones by conferring a survival advantage on gametocytes that carry resistant genes (23).
If, however, a medicine is combined with another that has transmission blocking activity
and different biochemical targets in the parasite, then it will block the transmission of
parasites resistant to the first. Thus, in an ACT, the artemisinin derivative will reduce
the likelihood of emergence and spread of parasites resistant to the partner medicine,
because it has short parasite clearance times and anti-infective properties (11,17,24).
Likewise, primaquine, when used in combination with a curative medicine, will reduce
the transmission of resistant mutants to the latter.

Whilst vector-control methods, such as residual insecticide spraying and the use of
insecticide-treated nets, can and will have an effect on the parasite population as a whole,
antimalarial medicines that block transmission will take effect only on parasites in the
infection which is being treated. This effect will be even smaller in high-transmission
settings, because of the infected persons who are ill, and it will constitute only a small
proportion of the parasite reservoir treatment; therefore, anti-infective drug treatment
will have less effect than vector-control methods in curtailing the spread of resistant
parasites.

Other important points are as follows:

• reducing transmission through mosquito control will help reduce the spread of drug
resistance;
• a therapeutic strategy to curtail the spread of drug resistant mutants will require a
combination of the curative medicines with one, which has infectivity suppressive
effects on the parasite targets of the two medicines being different. Both properties
residing in the same medicine will be unlikely to protect against the spread of resistant
parasites;
• such a therapeutic strategy will be synergistic with mosquito-control methods in
preventing the spread of drug resistance.

a4.4 summary and conclusions

Antimalarial medicines have an important role to play in reducing malaria transmission
and in curtailing the spread of drug resistant parasites. Early cure of blood infections,
such as by providing good access to diagnosis and treatment will, in itself, be effective
in lowering malaria transmission. Antimalarial medicines with specific infectivity
suppressive actions (e.g. artemisinin derivatives, primaquine) will reduce malaria
transmission even further and at almost all intensities of transmission, but particularly
in areas of low transmission.
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