Highly heterogeneous residual malaria risk in western Thailand

Nguitragool, Wang, Karl, Stephan, White, Michael, Koepfli, Cristian, Felger, Ingrid, Singhasivanon, Pratap, Mueller, Ivo, and Sattabongkot, Jetsumon (2019) Highly heterogeneous residual malaria risk in western Thailand. International Journal for Parasitology. (In Press)

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Abstract

Over the past decades, the malaria burden in Thailand has substantially declined. Most infections now originate from the national border regions. In these areas, the prevalence of asymptomatic infections is still substantial and poses a challenge for the national malaria elimination program. To determine epidemiological parameters as well as risk factors for malaria infection in western Thailand, we carried out a cohort study in Kanchanaburi and Ratchaburi provinces on the Thailand-Myanmar border. Blood samples from 999 local participants were examined for malaria infection every 4 weeks between May 2013 and Jun 2014. Prevalence of Plasmodium falciparum and Plasmodium vivax was determined by quantitative PCR (qPCR) and showed a seasonal variation with values fluctuating from 1.7% to 4.2% for P. vivax and 0% to 1.3% for P. falciparum. Ninety percent of infections were asymptomatic. The annual molecular force of blood-stage infection (molFOB) was estimated by microsatellite genotyping to be 0.24 new infections per person-year for P. vivax and 0.02 new infections per person-year for P. falciparum. The distribution of infections was heterogenous, that is, the vast majority of infections (>80%) were found in a small number of individuals (<8% of the study population) who tested positive at multiple timepoints. Significant risk factors were detected for P. vivax infections, including previous clinical malaria, occupation in agriculture and travel to Myanmar. In contrast, indoor residual spraying was associated with a protection from infection. These findings provide a recent landscape of malaria epidemiology and emphasize the importance of novel strategies to target asymptomatic and imported infections.

Item ID: 58121
Item Type: Article (Research - C1)
ISSN: 1879-0135
Keywords: malaria, epidemiology, Plasmodium vivax, Plasmodium falciparum, force of infection, prevalence, incidence, Thailand
Copyright Information: © 2019 Published by Elsevier Ltd on behalf of Australian Society for Parasitology.
Funders: Bill and Melinda Gates Foundation (BMGF), National Health and Medical Research Council (NHMRC), Swiss National Science Foundation (SNSF), Wellcome Trust (WT), National Institutes of Health (NIH)
Projects and Grants: NHMRC Project Grant 1021455, SNSF Grant 310030_159580, WT 101073/Z/13Z, NHMRC Senior Research Fellowship 1043345, NIH 5R01 AI 104822
Date Deposited: 22 Apr 2019 23:43
FoR Codes: 11 MEDICAL AND HEALTH SCIENCES > 1117 Public Health and Health Services > 111706 Epidemiology @ 60%
11 MEDICAL AND HEALTH SCIENCES > 1108 Medical Microbiology > 110803 Medical Parasitology @ 40%
SEO Codes: 92 HEALTH > 9204 Public Health (excl. Specific Population Health) > 920404 Disease Distribution and Transmission (incl. Surveillance and Response) @ 100%
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