Active Case Detection with Pooled Real-Time PCR to Eliminate Malaria in Trat Province, Thailand

Abstract

Abstract. We conducted contact tracing and high-risk group screening using pooled real-time polymerase chain reaction (PCR) to support malaria elimination in Thailand. PCR detected more Plasmodium infections than the local and expert microscopists. High-throughput pooling technique reduced costs and allowed prompt reporting of results.Thailand's National Malaria Control and Elimination Strategy aims to free 80% of the country from locally acquired malaria by the year 2020 (Bureau of Vector-Borne Diseases, Ministry of Public Health, Thailand, unpublished data). However, the elimination of local transmission requires rapid detection and treatment of all infections, including those infections in asymptomatic individuals who may serve as important reservoirs.1-3 Currently, malaria case detection for surveillance depends on microscopy or rapid diagnostic tests, but both methods miss low parasite densities on the order of 10 parasites/μL. Such submicroscopic infections are detectable by polymerase chain reaction (PCR) and are common in areas with low and unstable malaria. [4][5][6][7] Efforts to control and eliminate malaria from Trat province on the border with Cambodia are intensifying because of the potential spread of artemisinin resistance. The detection of submicroscopic cases may facilitate containment efforts and help preserve artemisinin-based combination therapies for effective malaria treatment (Bureau of Vector-Borne Diseases, Ministry of Public Health, Thailand, unpublished data).Real-time PCR is a highly sensitive tool for detecting and speciating Plasmodia. Pooling samples before analysis facilitates the large-scale application of this technique for surveillance by reducing cost and analysis time. 7,8 As Thailand aims for malaria elimination, including elimination of artemisininresistant parasites, improvements in case detection are necessary. We aimed to determine if pooled real-time PCR could be integrated with the existing active case detection systems in Thailand and if so, if it would be more effective than microscopy for identifying low-density parasitemias.A single index case, with mixed P. falciparum-P. vivax infection, was identified during hospitalization for severe malaria in July of 2011 through passive case detection. This infection was likely acquired during frequent forest exposure. Two weeks after this identification, 187 residents in Bo Rai district, Trat province, Thailand (Figure 1) were contacted over 3 days according to the policies of the National Malaria Control Program of Thailand, which includes contact tracing (Case Investigation Survey) and high-risk group screening (Special Case Detection). For contact tracing, we screened neighbors within 1 km of the index case. For high-risk group screening, we screened soldiers from Khao Lan and Ban Sapanhin army camps and residents of Takang and Ban Samoh villages, which have a high proportion of Burmese Mon migrants.We administered a questionnaire to collect demographic information and risk factors for malaria, such as history of fever a...

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