http://bmj.com/cgi/content/full/323/7307/251/b
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News
New strain of malaria reported in Africa
Scott Gottlieb
A deadly new strain of Plasmodium falciparum, the parasite that causes
malaria, has arrived in Africa, according to an article in the Wall
Street Journal (2001;26 Jul:B1).
Four different plasmodium species cause malaria, but P falciparum is the
most deadly. Several years ago a fourth mutation of P falciparum
emerged in parts of Asia and South America. Since then scientists
have been waiting for its appearance in Africa, where 90% of the
world's estimated one million deaths related to malaria occur each
year.
The article stated that about six months ago, while studying nine blood
samples taken from Tanzanian children infected with malaria, Carol
Sibley, a geneticist at the University of Washington in Seattle,
found that three samples had the mutated parasite. Until now her
discovery was not widely known, even among malaria specialists.
P falciparum has a long history of resisting drugs through changes in its
DNA. In Thailand the species has evolved resistance to chloroquine,
sulfadoxine-pyrimethamine, and mefloquine in succession. But the
latest mutation in Africa is especially alarming because it shields
the parasite from sulfadoxine-pyrimethamine, one of the most
affordable and widely used medicines in Africa. Scientists predict
that if sulfadoxine-pyrimethamine becomes ineffective the human toll
from malaria could escalate.
Most drugs target dihydrofolate reductase, a key enzyme in the synthesis of
deoxythymidine, histidine, and methionine. Sulfonamides target
dihydropteroate synthase, which is required for the synthesis of
folate. These drugs have been extremely effective in the past. In
most cases combinations of these drugs have been used because the
drugs act synergistically.
However, because the antimalarial drugs are only marginally effective, the
incredibly rapid development of resistant P falciparum strains has
made these drugs virtually useless in many regions. The parasites
are resistant to the drugs because they carry alleles of the
dihydrofolate reductase or dihydropteroate synthase genes that
encode mutant forms of the target enzyme. Combination therapy has
been advocated as the standard treatment to prevent the spread and
development of resistance to antimalarial drugs.
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