Large differences in variability for genes associated with antimalarial drug resistance between samples from Tanzania and Ethiopia

Background

Changes in antimalarial drug policy lead to selection of the most successful parasite clones. In spite of a change to Artemisinin Combination Therapy (ACT), we have earlier shown a low degree of variability for the chloroquine resistance marker pfcrt in samples of Plasmodium falciparum from Ethiopia with 100% carrying the crucial K76T variant [1].

Materials and methods

The study material was collected in the Shalla district, Oromia, Ethiopia, and in different parts of Tanzania. Genetic polymorphisms in the genes pfmdr1 and pfubp1 were analysed by PCR and nucleotide sequence determinations.

Results

A surprising finding was that a majority of Ethiopian isolates carried the wild type variant of pfmdr1. The majority of samples from different regions of Tanzania were wild type for both pfcrt and pfmdr1. Analysis of a variable linker region in pfmdr1 showed substantial variation in samples from Tanzania, but minimal variation in samples from Ethiopia. The variable part consists of consecutive NDN residues. The dominating variant in Ethiopians was 7/2/9 and 7/2/10 in Tanzania. The same pattern was seen for a variable part of the pfubp1 gene, where all Ethiopian samples were identical to 3D7. In 19 Tanzanian samples only 8 were identical to 3D7 with 5 other variants. A polymorphism at codon 1528, detected previously in Kenyan samples [2] was found in 2 Tanzanian samples.

Conclusions

While the presence of the mutant variant of pfcrt in the Ethiopian samples can be explained by continued use of chloroquine in Ethiopia for treatment of P. vivax, the selection of wild type pfmdr1 could be a consequence of using ACT for treatment of P. falciparum. In general, the variability in both studied genes was greater in Tanzania than in Ethiopia. There are no data yet to link the variability in pfubp1 to efficacy of ACT.