Treatment Failures

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Treatment Failures
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Treatment Failure under Endemic Conditions
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True Recrudescence
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Re-infection
Completely Different
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Multiple Genetic Markers
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P. falciparum polymorphic genes as genotyping
tools
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True Recrudescence or Re-infection?
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Resistance to chloroquine
The first stage of resistance to chloroquine is
now believed to be acquired through a mutation
in the pfcrt gene on chromosome 7 coding for
Pfcrt protein in the membrane of the lysosome.
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Pfcrt
LYSOSOME
Lys76thr associated with chloroquine-resistance
271
371
97
356
220
76 75 74 72

326
NH2
COOH
CYTOPLASM
CYTOPLASM
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Resistance to chloroquine
Resistance to chloroquine is slow to develop and
may involve mutations in at least 2 genes pfcrt
and pfmdr1 A pfcrt mutation permits resistance,
which in certain circumstances is enhanced by
pfmdr1 mutation(s)
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Pgh1
86
-
asn

tyr
-
184
tyr

phe
1034
-
ser
cys
1042
-
asn
asp
86
1246
-
asp
tyr
184
link
642
-
661
1042
11
1
3
5
7
9
1034
link
ATP
1246
ATP
NH
2
COOH
CYTOPLASM
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PCR/RFLP analysis of chloroquine resistance
marker pftcrt T76
M 1 2 3 4 5
Dd2 3D7 C M
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MECHANISMS OF RESISTANCE Antifolate drugs
dihydroneopterin
sulfonamides, sulfones
dihydropteroate
dihydrofolate
pyrimethamine, biguanides
Compete for active site with DHF
DHFR (TS)
tetrahydrofolate
Met Gly dTTP
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59
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Drug/substrate
108
Bolivia repeat
NADP
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164
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MECHANISMS OF RESISTANCEOther drugs
Compound class Drugs Gene Codon with
AA change
Naphtoquinine Atovaquone cytochrome
b Y268T
Amino-alcohols Mefloquine pfmdr1 copy number?
Halofantrine 86, 1034,
Quinine 1042, 1246
Sesquiterpene lactone Artemisinin pfmdr1
86, 1034, 1042, 1246
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Molecular markers

• Pro
• Easy to obtain a large number of samples on
  filter paper
• Cons
• Mutations for a small number of drugs
• CQ, PYR, SDX, atovaquone
• Identification of an epitope close to resistance
  epitope
• Mixed infections

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Molecular markers future

• Validation of markers
• genotype resistance index (GRI) prevalence
  genotype/prevalence clinical/parasitological
  failure
• epidemiological settings
• Identification of markers for other drugs
• Malaria species other than P. falciparum
• Centres of reference