Prevalence of Clinical and Subclinical Plasmodium falciparum and Plasmodium vivax Malaria in Two Remote Rural Communities on the Myanmar-China Border

Abstract

Malaria infections may be symptomatic, leading to treatment, or "asymptomatic," typically detected through active surveillance, and not leading to treatment. Malaria elimination may require purging both types of infection. Using detection methods with different sensitivities, we conducted a cross-sectional study in two rural communities located along the border between China's Yunnan Province and Myanmar's Shan and Kachin States, to estimate the prevalence of asymptomatic and symptomatic malaria. In Mong Pawk, all infections detected were asymptomatic, and the prevalence of Plasmodium falciparum was 0.3%, 4.3%, 4.0%, and 7.8% by light microscopy, rapid diagnostic test (RDT), conventional polymerase chain reaction (cPCR), and multiplexed real-time PCR (RT-PCR), respectively, and Plasmodium vivax prevalence was 0% by all detection methods. In Laiza, of 385 asymptomatic participants, 2.3%, 4.4%, and 12.2% were positive for P. vivax by microscopy, cPCR, and RT-PCR, respectively, and 2.3% were P. falciparum-positive only by RT-PCR. Of 34 symptomatic participants in Laiza, 32.4% were P. vivax-positive by all detection methods. Factors associated with infection included gender (males higher than females, P = 0.014), and young age group (5-17 age group compared with others, P = 0.0024). Although the sensitivity of microscopy was adequate to detect symptomatic infections, it missed the vast majority (86.5%) of asymptomatic infections. Although molecular detection methods had no advantage over standard microscopy or RDT diagnosis for clinically apparent infections, malaria elimination along the Myanmar-China border will likely require highly sensitive surveillance tools to identify asymptomatic infections and guide targeted screen-and-treat interventions.

Figure 1.

Web-based map of malaria prevalence in study sites. In the inserts showing Mong Pawk and Laiza sites, the white, blue, and purple color in the pie chart represents the proportion of study participants with no, Plasmodium vivax, and Plasmodium falciparum malaria, respectively. This figure appears in color at www.ajtmh.org.

Figure 2.

Prevalence of asymptomatic and symptomatic Plasmodium falciparum and Plasmodium vivax infection detected by microscopy, conventional nested polymerase chain reaction (PCR), and multiplex real-time PCR in study sites. Rapid diagnostic test (RDT) kits were available, and this test was conducted only in Mong Pawk. This figure appears in color at www.ajtmh.org.

Figure 3.

Prevalence of malaria by age group in two study sites. This figure appears in color at www.ajtmh.org.