Plasmodium falciparum response to chloroquine and artemisinin based combination therapy (ACT) in Guinea-Bissau

Abstract

Plasmodium falciparum causes the most severe form of malaria and is the most common malaria species in sub-Saharan Africa. Chloroquine used to be the most common drug for the treatment of malaria. Due to development of resistance, chloroquine is no longer efficacious in most of the world. The first line option for treatment of P. falciparum is now artemisinin based combination therapy, such as artemether-lumefantrine. In Guinea-Bissau, in contrast to the rest of Africa, chloroquine has been considered to be effective by practitioners in line with clinical trials by our group. Artemether-lumefantrine replaced chloroquine for the treatment of malaria in Guinea-Bissau in 2008.

The main aim of this thesis has been to study if and why chloroquine has remained efficacious in Guinea-Bissau.

We have shown that chloroquine resistance is associated with the CVIET haplotype at amino-acid positions 72-76 of the chloroquine resistance transporter (pfcrt). Genotyping and in vitro data presented in the thesis indicate that the proportion of resistant P. falciparum has been stable and low (~25%) since the early 90's. In line with that, P. falciparum with pfcrt 76T do not accumulate during the high transmission season, in Guinea-Bissau. Concurrently, approximately 3 times standard dose chloroquine has been routinely prescribed and taken without severe adverse events.

In a randomized clinical trial, we show that the PCR corrected day 28 and day 42 efficacies of double standard dose chloroquine were 95 and 94% respectively. The corresponding artemether-lumefantrine efficacies were 97%. Both antimalarial treatment options were well tolerated. The PCR corrected day 28 efficacies of double standard dose and standard dose chloroquine against P. falciparum with pfcrt 76T were 78-87% and 38%, respectively. Chloroquine concentrations were lower in children with PCR adjusted treatment failure compared to children with PCR adjusted adequate clinical and parasitological response by day 42. Recrudescent P. falciparum following treatment with artemether-lumefantrine or chloroquine appeared to carry opposite alleles at pfcrt codon 76 and multidrug resistance gene codon 86.

The dose and concentration dependent efficacy of chloroquine against P. falciparum with pfcrt 76T indicate that chloroquine resistance can be overcome by higher doses of chloroquine. High total chloroquine doses are well tolerated when split into repeated smaller daily doses. The lack of seasonal accumulation of pfcrt 76T indicates that the dosage schedule commonly used in Guinea-Bissau is efficacious and that pfcrt 76T is associated with a loss of fitness. Double standard dose chloroquine and artemetherlumefantrine fulfill the WHO efficacy requirements for antimalarials about to be adopted as treatment policy.