Malaria, more evidence of resistance to existing drugs
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Article Date: 18 November 2005
MIM Pan-African Malaria Conferences
Scientists are documenting increasing resistance to drugs that
have been mainstays of malaria treatment in disease endemic re-
gions of Africa, giving governments the evidence they need to
switch to new, more effective treatments. New treatments such as
ACT's are themselves being watched closely by scientists for
signs of failure, according to discussions at this week's Fourth
Multilateral Initiative on Malaria (MIM) Pan-African Malaria
Conference.
Researchers in Cameroon, for example, are presenting new pre-
liminary evidence confirming the declining effectiveness of com-
monly used malaria drugs, particularly sulfadoxine-pyrimethamine
(SP) but also amodiaquine (AQ), and the two in combination,
AQ+SP. (Tuesday, 3:20 p.m., Bubinga Hall, Parallel Session 9,
Presentation 57)
Wilfred Mbacham of the University of Yaounde a lead investigator
on the study, which was funded by the Gates Malaria Partnership,
said, "Scientists have known the drugs were losing their effec-
tiveness to varying degrees but we lacked comprehensive data
showing precisely how people in Cameroon responded to the medi-
cations. Such analysis is critical to providing solid support
for changing treatment policies to those that advocate replacing
older drugs with newer so-called artemisinin-based combination
therapies or ACT's."
Scientists have found that malaria today responds quickly and is
less likely to develop resistance to a course of treatment that
combines artemisinin, a particularly potent antimalarial derived
from the wormwood plant, with another antimalarial. The chal-
lenge now for many governments is to procure sufficient supplies
of ACT's both at a price that is affordable and in a form that
simplifies treatment.
In addition, Mbacham said another challenge is to systematically
monitor patients and the malaria parasite for any signs of re-
sistance emerging to ACT's. For example, he said scientists are
studying parasites in malaria endemic areas for evidence of any
genetic mutation that may be linked with an ability to overcome
ACT's.
But as his recent study of drug resistance in Cameroon -- which
involved more than 750 patients at three different sites -- re-
vealed, resistance can be difficult to detect as responses to
malaria medications can vary among different populations.
"We were surprised to find that between populations in the north
and the south of Cameroon, there are different levels of resis-
tance to certain malaria drugs, between the north and the
south," said Mbacham. "We know that there are genetic differ-
ences between the parasite populations in the north compared to
the south, but we do not know whether that increases responsive-
ness to the drugs or not. We also know that you can compare dif-
ferent West African populations living side by side and find
different levels of malaria-specific antibodies which may also
affect treatment outcome."
Robert Guiguemde of the Muraz Center in Burkina-Faso, who is
chairing the MIM session on drug resistance, said the critical
issue now is preventing the emergence of resistance to ACT's in
Africa, and that will require educating patients about the need
to adhere to a specific treatment regimen.
"We often see people stopping their treatment as soon as they
feel better," he said. "But even if they believe they have re-
covered, there are still parasites in their system that have not
all been killed and those that remain are likely to be the para-
sites least sensitive to the drug. They will then multiply and
spread and the drugs will start losing their effectiveness."
"A key to keeping track of resistance is to maintain the re-
search capacity in Africa required to routinely monitor both
people and parasites," said Andreas Heddini, the MIM Secretariat
coordinator. "You need the scientists on the ground collecting
blood samples in different populations and different geographic
areas, and you need the laboratory instrumentation and expertise
required to quickly probe these samples for some of the known
genetic markers of resistance. We also need to study patient be-
havior since resistance can be linked to a variety of behavior
issues, such as whether people take a full course of treatment."
The MIM conference will feature several presentations offering
evidence of parasite resistance to familiar malaria drugs and
the challenges of replacing these treatments with ACT's. For ex-
ample:
- - Michael Alifrangis of the Center for Medical Parasitology in
Copenhagen will discuss a study that found evidence in blood
samples taken in two villages in northern Tanzania of a genetic
variation in the malaria parasite that may be associated with an
ability to resist amodiaquine (AQ), which is sometimes used in
combination with artemisinin. The study notes that while amo-
diaquine resistance has been noted at several sites in Africa,
the genetic variation linked to resistance had not yet been ob-
served on the continent. Researchers conclude that "its occur-
rence on the African continent is of great concern to the future
use of AQ, including in artemisinin-based combination." (Thurs-
day, 12:25 p.m., Ebony Hall, Parallel Session 22, Presentation
145)
- - New data from a study of children in Western Kenya chal-
lenges the position that ACT's can substantially reduce trans-
mission of malaria by clearing children of the malaria parasite
at the stage in its lifecycle in which it is passed from humans
back to mosquitoes. Researchers from the Radboud University
Medical Center in the Netherlands, along with colleagues from
Kenya's International Center for Insect Physiology and Ecology
(ICIPE) and the Kenyan Medical Research Institute (KEMRI), found
that the majority of ACT-treated children they studied were ca-
pable of infecting mosquitoes. "The presented findings are so-
bering for future interventions aimed at reducing malaria trans-
mission by the use of antimalaria drugs," the study concludes.
(Wednesday, 1:00 p.m., Poster Session 8, Poster 143B)
- - While ACT's are now the preferred treatment for malaria, Tom
Sukwa of the World Health Organization's Regional Office for Af-
rica will present a report that notes, among other things, that
ACT's cost ten times more than once commonly used--but increas-
ingly ineffective--drugs. His presentation will also address the
fact that there is only one "pre-qualified fixed formulation of
ACT registered with WHO and that, in 2005, demand exceeded sup-
ply." The report also considers the need for more data on the
safety of ACT's and the lack of oversight systems in African
countries for monitoring adverse reactions. (Thursday, 2:50
p.m., Bubinga Hall, Parallel Session 25, Presentation 161)
--
Preeti Singh
MIM Pan-African Malaria Conferences
mailto:psingh@burnesscommunications.com
http://www.mim.su.se/conference2005/eng/overview.html
--
Leela McCullough, Ed.D.
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