Prevalence of Asymptomatic and Sub-Microscopic Malaria Infection During Non-Transmission Season: A Community Based Cross-Sectional Study in Districts of North-Eastern Region, India

Background: Malaria elimination requires targeting asymptomatic sub-microscopic malaria which largely remained undetected hidden reservoir of infection to sustain malaria transmission. The pre-requisite of malaria elimination programme requires early screening, prompt detection and complete treatment of asymptomatic/ sub-microscopic infection. Thus, the present study was aimed to estimate the prevalence of asymptomatic and sub-microscopic malaria burden in high and low endemic regions in North east India by comparing the sensitivity of diagnostic tools utilized by Government Health Agencies with the molecular technique. Methods: The mass blood surveys were conducted in high and low malaria-endemic areas of two north-eastern districts of India using a probability proportion to size method. All available individuals were screened for malaria irrespective of any clinical sign and symptoms. Finger prick blood was collected for on-spot diagnosis using rapid diagnostic test kit (RDK), thick and thin blood smear for light microscopy and dried blood spot on filter paper for molecular diagnosis. History of fever and other clinical signs and symptoms related to malaria were recorded along with measuring axillary body temperature. Findings: A total of 9118 participants were screened that showed overall malaria prevalence was 6·5%, 2·2% and 11·1% when tested with RDK, microscopy and PCR respectively. Among asymptomatic, malaria prevalence was found to be 6·0%, 1·9% and 11·0% using RDK, microscopy and PCR respectively. In addition, a significant proportion of malaria positive patients were asymptomatic ~82% (using microscopy)–85% (using PCR). The prevalence of sub-microscopic malaria was 57·3%, of which 88·9% were asymptomatic. The geographic differences and age-wise dispersion was observed for the likelihood of malaria infection, the prevalence of asymptomatic and sub-microscopic malaria. Of 8228 participants who underwent haemoglobin testing, 55·2% were anaemic, of which 24·9% were mild, 28·8% moderate and 1·6% were severely anaemic. The diagnostic accuracy of microscopy was lesser than RDK in comparison to PCR, and further much lesser in low compared to high malaria-endemic areas. Interpretation: The result suggests that there is a need to deploy molecular tools even when microscopy/ RDK malaria results indicate low prevalence, to curtail undetected infectious reservoir and accelerate malaria elimination programme. Funding Statement: The study was funded by the Indian Council of Medical Research, New Delhi, India. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: The study was approved by the Institution Ethics Committee of National Institute of Malaria Research (Ref. No.# ECR/NIMR/EC/2015/490).