Recent studies have shown that Plasmodium falciparum malaria parasites in Pailin province, along the border between Thailand and Cambodia, have become resistant to artemisinin derivatives. To better define the epidemiology of P. falciparum populations and to assess the risk of the possible spread of these parasites outside Pailin, a new epidemiological tool named “Focused Screening and Treatment” (FSAT), based on active molecular detection of asymptomatic parasite carriers was introduced in 2010. Cross-sectional malariometric surveys using PCR were carried out in 20 out of 109 villages in Pailin province. Individuals detected as P. falciparum carriers were treated with atovaquone-proguanil combination plus a single dose of primaquine if the patient was non-G6PD deficient. Interviews were conducted to elicit history of cross-border travel that might contribute to the spread of artemisinin-resistant parasites. After directly observed treatment, patients were followed up and re-examined on day 7 and day 28. Among 6931 individuals screened, prevalence of P. falciparum carriers was less than 1%, of whom 96% were asymptomatic. Only 1.6% of the individuals had a travel history or plans to go outside Cambodia, with none of those tested being positive for P. falciparum. Retrospective analysis, using 2010 routine surveillance data, showed significant differences in the prevalence of asymptomatic carriers discovered by FSAT between villages classified as “high risk” and “low risk” based on malaria incidence data. All positive individuals treated and followed-up until day 28 were cured. No mutant-type allele related to atovaquone resistance was found. FSAT is a potentially useful tool to detect, treat and track clusters of asymptomatic carriers of P. falciparum along with providing valuable epidemiological information regarding cross-border movements of potential malaria parasite carriers and parasite gene flow.

BackgroundIn December 2005 free long lasting insecticidal nets were distributed to mothers of children under five in a nation-wide scheme in Niger. More than 2 million bed nets were distributed, increasing the ownership of insecticide treated bed nets more than tenfold. Materials and methodsOur team was in charge of the malaria survey. The malaria cases were reported through a network of 44 sites across the country. Malaria transmission was surveyed in 12 villages in the Sahel, as it was deemed the most variable zone. Results and discussionDuring the first year of follow-up, vector dynamics showed an overall decrease in malaria transmission, but this was highly variable from village to village. Indeed, the second year of survey showed a return to transmission levels close to the pre-intervention period. A study of microsatellite markers showed no modification of the genetic structure in the two malaria vectors An. gambiae and An. arabiensis. However, a clear increase of the resistant allele of the kdr gene -resistence to the pyrethroid insecticide used in the bed nets -was observed. This clearly demonstrated that the main target vectors were reached. As measured by ovarian tracheoles observation, the parity rate of vectors was not significantly decreased. However, the index sporozoite decreased in the first year and remained low in the second year. Indeed, the parasite prevalence and the gametocyte carriage were shown decreasing in the children under five. This continued in 2007 as the National Malaria Control Program provided free artemisinin-based combination therapies as first line treatment for malaria in children under five. The national survey network showed a decrease in malaria cases, as confirmed in our sentinelle sites. However the biological confirmation of cases by HRP2 plasmodial antigen research has increased during the two years of follow-up. This could be explained by the more accurate diagnosis by peripheral health personal with the help of rapid diagnostic tests. ConclusionOur survey system allowed the report of the malaria evolution during that important period of control reinforcement in Niger. The causative impact was difficult to confirm because several lines of malaria control have been successively implemented. Moreover, the high climatic variability in this zone needs to be taken in account in the analysis. Despite these difficulties our data reinforce the importance of malaria monitoring through multidisciplinary studies to the benefit of control operations. AcknowledgementsFunded by the Global Fund and the World Health Organization.