Evidence of asymptomatic submicroscopic malaria in low transmission areas in Belaga district, Kapit division, Sarawak, Malaysia

Abstract

Background Malaysia has declared its aim to eliminate malaria with a goal of achieving zero local transmission by the year 2020. However, targeting the human reservoir of infection, including those with asymptomatic infection is required to achieve malaria elimination. Diagnosing asymptomatic malaria is not as straightforward due to the obvious lack of clinical manifestations and often subpatent level of parasites. Accurate diagnosis of malaria is important for providing realistic estimates of malaria burden and preventing misinformed interventions. Low levels of parasitaemia acts as silent reservoir of transmission thus remains infectious to susceptible mosquito vectors. Hence, the aim of this study is to investigate the prevalence of asymptomatic submicroscopic malaria (SMM) in the District of Belaga, Sarawak. Methods In 2013, a total of 1744 dried blood spots (DBS) were obtained from residents of 8 longhouses who appeared healthy. Subsequently, 251 venous blood samples were collected from residents of 2 localities in 2014 based on the highest number of submicroscopic cases from prior findings. Thin and thick blood films were prepared from blood obtained from all participants in this study. Microscopic examination were carried out on all samples and a nested and nested multiplex PCR were performed on samples collected in 2013 and 2014 respectively. Results No malaria parasites were detected in all the Giemsa-stained blood films. However, of the 1744 samples, 29 (1.7%) were positive for Plasmodium vivax by PCR. Additionally, of the 251 samples, the most prevalent mono-infection detected by PCR was Plasmodium falciparum 50 (20%), followed by P. vivax 39 (16%), P. knowlesi 9 (4%), and mixed infections 20 (8%). Conclusions This research findings conclude evidence of Plasmodium by PCR, among samples previously undetectable by routine blood film microscopic examination, in local ethnic minority who are clinically healthy. SMM in Belaga district is attributed not only to P. vivax , but also to P. falciparum and P. knowlesi. In complementing efforts of programme managers, there is a need to increase surveillance for SMM nationwide to estimate the degree of SMM that warrant measures to block new transmission of malaria.

Molecular methods for tracking residual Plasmodium falciparum transmission in a close-to-elimination setting in Zanzibar

“…Meta-analyses comparing prevalence rates determined by PCR versus LM have demonstrated that the proportion of submicroscopic P. falciparum infections in community samples substantially increases with declining malaria transmission intensity [14,15]. This trend was confirmed in the past few years by numerous molecular-epidemiological studies [15][16][17][18][19][20][21].…”

Malaria distribution and performance of malaria diagnostic methods in Malaysia (1980-2019): a systematic review

“…In this review, 12 studies relied solely on microscopy for Plasmodium detection and species differentiation. The use of microscopy as the sole diagnostic method likely leads to an underestimation of the malaria burden in a speci c population (75), particularly in P. knowlesi and P. malariae infections that usually present at densities below the limit for microscopic detection (24). This review also provided insight in the disparity between microscopy and PCR in diagnosing malaria cases.…”

“…namely P. malariae or P. knowlesi. Furthermore, of the 28 studies, ten studies (12,24,25,28,31,34,41,52,61,63) conducted PCR in the whole samples regardless of the microscopy results in order to trace the sub-microscopic infections. In addition, 18 studies utilised only one method of detection for malaria.…”

Malaria distribution and performance of malaria diagnostic methods in Malaysia (1980-2019): a systematic review

“…Of those 18 studies tested for PCR, ten studies (7-9, 36-38, 41, 54, 56, 60) used all the microscopy positive cases, six studies (5,33,47,49,51,52) used more than 70% of the cases, one study (48) used 2.5% randomly selected cases, and one study (39) used 19% of microscopy positive cases for either P. malariae or P. knowlesi. Furthermore, of the 28 studies, ten studies (12,24,25,28,32,35,42,53,63,65) conducted PCR on all samples regardless of the microscopy results in order to trace the sub-microscopic infections. In addition, 18 studies utilised only one method of detection for malaria: 15 (34, 43, 44, 46, 50, 55, 57-59, 61, 62, 64, 66-68) by microscopy and three (27,40,45) by PCR.…”