Importance of household-level risk factors in explaining micro-epidemiology of asymptomatic malaria infections in Ratanakiri Province, Cambodia

Melanie Bannister-Tyrrell,Set Srun,Wim Van Bortel,Vanna Mean,Mao Sokny,Lies Durnez,Vincent Sluydts,Sochantha Tho,Koen Peeters Grietens,Didier Menard,Saorin Kim,Charlotte Gryseels,Marc Coosemans

doi:10.1038/s41598-018-30193-3

Abstract

Heterogeneity in malaria risk is considered a challenge for malaria elimination. A cross-sectional study was conducted to describe and explain micro-epidemiological variation in Plasmodium infection prevalence at household and village level in three villages in Ratanakiri Province, Cambodia. A two-level logistic regression model with a random intercept fitted for each household was used to model the odds of Plasmodium infection, with sequential adjustment for individual-level then household-level risk factors. Individual-level risk factors for Plasmodium infection included hammock net use and frequency of evening outdoor farm gatherings in adults, and older age in children. Household-level risk factors included house wall material, crop types, and satellite dish and farm machine ownership. Individual-level risk factors did not explain differences in odds of Plasmodium infection between households or between villages. In contrast, once household-level risk factors were taken into account, there was no significant difference in odds of Plasmodium infection between households and between villages. This study shows the importance of ongoing indoor and peridomestic transmission in a region where forest workers and mobile populations have previously been the focus of attention. Interventions targeting malaria risk at household level should be further explored.

Highlights

Heterogeneity in malaria risk is considered a challenge for malaria elimination
Though it remains unclear the extent to which asymptomatic infections contribute to malaria transmission[7], achieving malaria elimination will likely require reduction of the prevalence of Plasmodium infection to zero for sustained interruption of transmission[5]
The Greater Mekong Sub region (GMS) is a global priority region for malaria elimination, due to the multiple emergence and spread of P. falciparum strains that are resistant to artemisinin-based combination therapies, the current first-line treatments for P. falciparum worldwide[16]

Summary

Introduction

Heterogeneity in malaria risk is considered a challenge for malaria elimination. A cross-sectional study was conducted to describe and explain micro-epidemiological variation in Plasmodium infection prevalence at household and village level in three villages in Ratanakiri Province, Cambodia. The assumption behind identifying and targeting malaria hotspots is that infections within hotspots contribute to maintaining the parasite reservoir in a way that infections outside the hotspots do not, and that eliminating malaria from hotspots would lead to interruption of transmission in adjoining areas[11]. Evidence for this premise remains scant; the first trial of its kind showed no effectiveness of hotspot targeting on community-wide malaria prevalence in Kenya[15]. Sleeping overnight at farms was previously shown to increase risk of Plasmodium infection[27], and outdoor evening activities have been postulated as increasing risk of infection through exposure to early evening, outdoor biting vectors[20,29]

Methods

Results

Discussion

Conclusion