The presence of P. vivax malaria in sub-Saharan Africa has been largely neglected since it was demonstrated that lack of expression of the Duffy blood-group correlated with the absence of P. vivax infections . Moreover, it has been suggested that P. vivax is of African origin thus driving fixation of the Duffy negative phenotype . Recent evidence, however, has called upon to revise this suggestion as it strongly indicates that P. vivax may instead be of Asian origin [16, 17]. Its increasingly recognized presence in Africa may, therefore, be related to its newly acknowledged capacity of exploiting new alternative invasion pathways among populations in this continent. Regardless of the geographical origin of P. vivax and the pathway for entrance into reticulocytes, it is clear that the presence of P. vivax in Africa is probably underestimated.
A few reports, of variable quality, have described infections by P. vivax in Mali [10–12]. An early indication of its presence came from the description of Russian doctors in the region of Gao in the 1950s (OD, unpublished). Four decades later, a case of P. vivax infection in an eight year-old girl was reported in Kidal during a survey in 1988 in Trans-Sahara . The microscopy diagnosis of this patient was confirmed in two European reference laboratories at Marseille and London. More recently, Koita et al. performed two cross-sectional studies in the North-Eastern region of Mali, reporting over 10% prevalence rates of P. vivax infections as detected by Giemsa-stained smear . However, and noteworthy, with the exception of one single sample, exclusion of the potentially confounding and morphologically similar P. ovale and P. malariae species were not systematically performed using molecular techniques.
Microscopy evaluation of samples examined here similarly suggested the presence of parasite blood stages resembling P. vivax. However, and as an important limitation of only using such diagnostic techniques, it seems difficult to exclude that these stages may not correspond to P. ovale species. P. ovale has been frequently reported in this particular region of Africa and even though distinct ameboid trophozoites and number of nuclei per single schizont can be used as criteria for species-specific diagnostics, this remains very challenging in most thick-blood smears. Thus, nested-PCR and DNA sequence analyses were performed to unambiguously demonstrate P. vivax infections in Mali. Amplified fragments of sizes corresponding to the SSU RNA gene of P. vivax were observed in close to 28% of infections. Moreover, sequence similarity and phylogenetic analyses unequivocally confirmed that these fragments corresponded to P. vivax sequences.
These findings are of important public health relevance. In recent years, the scientific attention of the malaria community has shifted from a focus on malaria control to specific efforts aiming at global malaria eradication . However, it is important to consider that efforts needed to control P. vivax will surely exceed those necessary to control P. falciparum as transmission of this species is possible even before the appearance of clinical symptoms, and can also occur irrespective of adequate asexual parasite clearance as a result of hypnozoite-derived relapses. Indeed, the adequate treatment of P. vivax infections includes the addition of a full 14-day long course of primaquine (PQ), the only to date registered drug that can achieve the radical cure of the hepatic hypnozoites, responsible for unpredictable relapses and subsequent morbidity, and a drug that has potent gametocytocidal activity. Without the radical cure, hepatic hypnozoites will maintain those infected individuals as infectious, and thus prone to maintain transmission and develop new disease episodes. PQ is unfortunately an unsafe drug, and can lead to severe haemolysis when administered blindly to glucose-6-phosphate dehydrogenase (G6PD) deficient patients, a genetic deficiency particularly frequent in sub-Saharan Africa, limiting therefore its widespread use unless guaranteeing prior screening of this deficiency. As no rapid G6PD deficiency diagnostic tests exist to date, dismissing its risks prior to PQ administration appears unfeasible, and adequate treatment of P. vivax episodes unguaranteed, adding further complexity to the control programmes in place in many African settings. In Mali, the spread of P. vivax in the northern part of the country will complicate the possibility of malaria elimination. The current malaria control programme has no reference to vivax malaria. The findings reported here will push further to a revision of the policy document. New tools will be needed (the use of mass drug administration of primaquine for example) and access to the target population is a major public health issue. All the laboratory technicians in this endemic region of P. vivax, should be retrained for microscopic diagnostic.
An important limitation of this work is the inability to link such confirmed P. vivax infections with the Duffy and G6PD phenotypes of the individuals affected. Indeed, the presence of Duffy positive ethnic groups in central and West Africa as in the case of the Moors in Mauritania  or other Ethnic groups that may be present in Mali could entirely account for P. vivax transmission in the area, and would not necessarily imply that this species has found alternative mechanisms to infect Duffy-negative individuals. Prospective studies further investigating the Duffy and G6PD status and its relation to species-specific malaria risk are, therefore, urgently needed.
In Mali, P. vivax infections can no longer be considered rare or anecdotal, and their diagnosis and adequate management need to be included as part of routine surveillance activities. This should be coupled with an adequate knowledge of the Duffy and G6PD status in the population, so as to assess the risks that the introduction of PQ treatment could entail to the population. Malaria control efforts in the area will surely fail unless species-specific measures are put in place.