Impact of the National Malaria Control Program and an Interventional trial with topical repellents on the burden of malaria disease in Ratanakiri province, Cambodia

Date: 27 April 2017

Venue: UAntwerp, Campus Drie Eiken, Building Q, Promotiezaal - Universiteitsplein 1 - 2610 Wilrijk (route: UAntwerpen, Campus Drie Eiken)

Time: 4:00 PM - 6:00 PM

PhD candidate: Somony Heng

Principal investigator: Marc Coosemans

Short description: PhD defence Somony Heng - Department of Biomedical Sciences

Malaria heterogeneity and early/outdoor biting vectors are the great challenges to Cambodian malaria elimination goal. Adding efficacious intervention tools to current ones could synergize effectiveness on malaria prevention. Success of an intervention tool does not depend on its intrinsic efficacy only, but also on its implementation ease and achieved coverage. This thesis explores the malaria heterogeneity and its implications for adapting the malaria elimination strategy. The thesis evaluates also the impact of mass-use of topical repellents (picaridin) in addition to long lasting insecticidal nets (LLINs) on the incidence of malaria in Ratanakiri Province (part a cluster randomized trial).

Provincial malaria incidence trends were estimated (2010-2014). Spatial clustering analysis of malaria cases and malaria infections was performed. Malaria risk factors were explored. The distribution of repellents in terms of contact with the households and product consumption was evaluated and their determinants were explored. To assess the safety of repellents reported side effects and individual adverse events (AEs) through home visits were recorded. Comparison of incidence between treatment arms (repellents+ LLINs versus LLINs alone) was performed to evaluate additional value of mass-use of mosquito repellent.

Malaria incidence per 1000 inhabitants decreased from 86 in 2010 to 30 in 2014. Significant and stable clusters were found along Cambodian-Vietnamese border and Sesan River. Overnight stay in plot hut was the main risk factors of malaria infection. Distributor-household contact increased by four and repellent consumption rates tripled in 2013 compared to 2012. District, commune and knowing distributor were determinants of contact; while district and household head occupation were determinants of consumption. Of 41 AEs, 22 were moderate adverse reactions (ARs), 11 repellent abuses and eight non-related events. Of abuse cases, three had moderate severity and two were life-threatening. All cases recovered completely. Annual malaria incidence rates did not differ between the two arms of the cluster randomized trial.

The decline of malaria incidence can be attributed to national intensive control activities. Malaria elimination programs should implement additional interventions targeting households in the clusters with higher malaria and people staying overnight in the plot hut. With programmatic and logistic support, the distribution of repellent was successful. ARs and abuse cases during picaridin mass use were uncommon and generally mild. Adding mass-use of picaridin to LLIN induced no additional community protection in controlling malaria incidence and this despite high repellent efficacy and excellent accessibility. Daily use compliance was too low to synergize the impact of LLINs on malaria reduction.