Chloroquine resistance status a decade after: Re-emergence of sensitive Plasmodium falciparum strains in malaria endemic and epidemic areas in Kenya

Development and spread of chloroquine (CQ) resistance led to its withdrawal in most malaria endemic countries. In Kenya, this occurred in 1998 when clinical efficacy dropped below 50%. Less than a decade after CQ was removed from routine use in Malawi, the drug has reversed to activity and is again effective for first-line treatment of uncomplicated malaria. There is a probability of a similar reversed activity in Kenya for more 10 years of its absence in uncomplicated Plasmodium falciparum malaria treatment. The present study was aimed at establishing the CQ resistance status in the country, 10 years after its withdrawal, by looking at high malaria transmission zone, Mbita, a malaria endemic area and some malaria epidemic areas of the Kenyan highlands. The prevalence of T76 and Y86 P. falciparum molecular markers for CQ resistance in Pfcrt and Pfmdr1 genes were investigated by PCR-RFLP and dot blot analysis in 64 samples collected in March to May 2007 in the endemic area and 38 samples collected in April to July the same year in the epidemics. The study shows that 67.3% of field isolates from the endemic site still harbor Y86 mutation in Pfmdr1 while 32.7% have the wild type allele N86 compared to the 94% and 6 % prevalence observed in Mwea, an endemic area, in 2004 (χ 2 =10.08, P=0.00015, 95% CI=2.085-27.8). In the epidemics 75% of field isolates from the epidemic sites still harbor Y86 mutation in Pfmdr1 while 25% have the wild type allele N86 compared to the 91.6% and 8.4% prevalence observed in an epidemic area in 1997 (χ 2 =1.585, P=0.208, 95% CI=0.701-19.176). From the study there is a significant change in the proportions of the resistant genotypes in the endemic areas while in the epidemics, there was also a noticeable shift though not significant. This therefore indicates a slow but steady re-emergence of P. falciparum CQ sensitive strains in the country. Though does not warrant the reintroduction of CQ for malaria treatment.