Ethiopia comprises regions of largely differing malaria endemicity and transmission. Considering the substantial burden of disease in this country, there is a remarkable shortage on country-wide data on the efficacy of antimalarial drugs. A failure rate of 88% within two weeks following CQ treatment was reported from central Ethiopia already in 1999 . A recent multi-site survey demonstrated mean SP treatment failure rates of 36% and 72% within two and four weeks of follow-up, respectively . AL, in contrast, was reported to achieve adequate clinical and parasitological response in 99% .
In line with reports on high clinical failure rates of CQ and SP, the obtained data shows that in an area of seasonal transmission in southern Ethiopia, P. falciparum mutations conferring resistance to these drugs are abundant. In particular, pfcrt T76 and the pfdhfr triple mutation occurred in 100% and almost 90%, respectively. Also, pfdhfr G437 and E540 considered to confer high grade SP resistance in the presence of the pfdhfr triple mutant  were seen in all but two P. falciparum isolates. In addition, with the exception of pfmdr1, mixed alleles comprising both wildtype and mutation, were absent. Although only approximative evidence, this suggests a rather low multiplicity of infection according with the seasonal nature of malaria transmission in the study area.
The prevalence of pfdhfr triple and pfdhfr/pfdhps quintuple (86%) mutations found in this study is extraordinarily high. In Malawi, roughly three out of four patients infected with parasites exhibiting quintuple mutations have been reported to suffer SP treatment failure . So far, the predictive value of these markers for SP treatment failure has neither been established in Ethiopia nor in the study area. Though this predictive value may show some variation between different locations [10, 11], however, overall and considering respective studies in East Africa [23, 10] these findings match with the extremely poor SP efficacy rates seen in this country . In Jima, southern Ethiopia and some 200 km West of Dilla, 54% of P. falciparum isolates have recently been reported to carry the pfdhfr/pfdhps quintuple mutation  highlighting the uneven distribution of drug resistance in the country. Furthermore, the prevalence of quintuple mutants in the present study exceeds respective numbers in other African countries where SP had been used for a longer period of time [23, 25]. The reason for the abundance of mutations conferring SP resistance in the study area of Dilla remains obscure but the findings definitely supports usage of an alternative first-line drug, e.g. AL.
Pfcrt T76, and to a lesser extent pfmdr1 Y86, are useful markers of CQ resistance in areas where it is low to moderate [20, 26]. In the present study, the high prevalence of pfcrt and pfmdr1 mutations match the known poor efficacy of CQ in Ethiopia . However, considering the retraction of the drug at least from official first-line treatment, perpetuation of resistant strains in the parasite population due to ongoing CQ usage also seems possible. Unfortunately, pre-treatment drug levels could not be assessed in the present study. Nevertheless, the obtained results on CQ resistance markers may have importance for subsequent monitoring: In areas where CQ was abandoned as first-line antimalarial, a recovery of CQ sensitivity and a decrease of pfcrt mutations have been demonstrated [27, 28].
For P. vivax, high frequencies of pvdhfr N117 (94%) and N117-R58 (74%) variations but no T117, triple or quadruple mutations were observed. Although these multiple mutations seem to be necessary for in vivo resistance [13, 14], this finding suggests widespread SP use since the former arise first under drug pressure [13, 14]. Higher frequencies of pvdhr mutations are only found in Thailand where double and triple mutations were detected in 99% of isolates . P. vivax substantially contributes to morbidity in Ethiopia and differentiating P. falciparum from P. vivax frequently is hampered by limited or absent microscopic facilities. As this implies SP treatment of P. vivax malaria, monitoring the resistance patterns seems worthwhile.