Plasmodium vivax accounts for about 40% of all malaria infection in Ethiopia. Chloroquine (CQ) is the first line treatment for confirmed P. vivax malaria in the country. The first report of CQ treatment failure in P. vivax was from Debre Zeit, which suggested the presence of chloroquine resistance. METHODS: An in vivo drug efficacy study was conducted in Debre Zeit from June to August 2006. Eighty-seven patients with microscopically confirmed P. vivax malaria, aged between 8 months and 52 years, were recruited and treated under supervision with CQ (25 mg/kg over three days). Clinical and parasitological parameters were assessed during the 28 day follow-up period. CQ and desethylchloroquine (DCQ) blood and serum concentrations were determined with high performance liquid chromatography (HPLC) in patients who showed recurrent parasitaemia.

CONCLUSION: Chloroquine-resistant P. vivax parasites are emerging in Debre Zeit, Ethiopia. A multi-centre national survey is needed to better understand the extent of P. vivax resistance to CQ in Ethiopia BACKGROUND: Plasmodium vivax malaria is the most geographically widespread and the second prevalent cause of malaria globally. Among 2.6 billion people at risk of malaria infection, annual estimates of P. vivax cases range from 130 to 435 million [1], 90% of these infections occur outside Africa [2]. Ethiopia has the highest proportion of P. vivax malaria on the continent, accounting for approximately 40% of all infection in the country [3]. Chloroquine (CQ) is the first line treatment for P. vivax malaria in most parts of the world. However, CQ resistance in P. vivax has compromised its use since the first reported cases from Papua New Guinea in 1989 [4]. Since then, cases of resistance have been reported from places such as Indonesia, island of Nias, in Papua and Irian Jaya in 1991 [5], Myanmar in 1993 and 1995 [6,7], India in 1995 [8], Borneo in 1996 [9], and in south America; Guyana in 1996 [10], and parts of the Amazon Brazil [11-13], Columbia in 2001 [14], Vietnam in 2002 [15], and Peru in 2003 [16]. Resistance has also been reported from two areas in Turkey in 2004 [17]. To date prevalence as high as 84% of CQ-resistant P. vivax has been reported from the north-eastern coast of Indonesian Papua in 2003 [18]. CQ has also been the first line drug in Ethiopia for uncomplicated malaria since 1950. Following the findings of CQ treatment failure as high as 65% for P. falciparum in studies conducted at 18 sites between 1997/98 [19], sulphadoxine/pyrimethamine (SP) was introduced as a first line drug treatment for uncomplicated falciparum malaria in 1999 [20]. SP was replaced by artemether/lumefantrine (AL) five years later after a study conducted in 2003 in 11 sites showed 35.9% treatment failure at day 7 and 71.7% on day 28. The efficacy of AL was reported to be 99.1% in 2004, when it replaced SP [21]. However, CQ continued to be in use as first line drug for vivax malaria. The first report of P. falciparun and P. vivax CQ treatment failure in Debre Zeit, was in 1995, when only 4 of 29 (14%) P. falciparum patients cleared their asexual parasites by day 7 and 2% of 225 P. vivax patients who were followed for seven days failed to respond to CQ treatment [22]. Malaria is one of the most frequently diagnosed acute illnesses and a principal cause of morbidity affecting all age groups in Debre Zeit. Transmission occurs throughout the year with P. vivax being more prevalent (70%) than P. falciparum (30%). Malaria transmission is generally more intense following the main rainy season, which occurs from September to December. The aim of the present study was to determine the rate of CQ treatment failure in P. vivax and confirm whether treatment failure is due to drug resistance or sub-therapeutic antimalarial drug concentrations.