A saliva-based rapid test to quantify the infectious subclinical malaria parasite reservoir.

Dingyin Tao,Bruce Shull,Andrew Walzer,Timothy Hamerly,Paul D Slowey,Andrew Holtz,Prachi Khare,Rashid Ansumana,David J Sullivan,Rhoel R Dinglasan,Sadie J Ryan,Amanda Dziedzic,Isabelle Morlais,Mike Chaponda,David A Stenger,Sandrine E Nsango,Modest Mulenga,Kathryn H Jacobsen,Brent Mcgill,Christopher C Slowey,William J Moss,Kunihiko Tamaki ,Anne Jedlicka ,Tomasz A Łęski

doi:10.1126/scitranslmed.aan4479

Abstract

A large proportion of ongoing malaria parasite transmission is attributed to low-density subclinical infections not readily detected by available rapid diagnostic tests (RDTs) or microscopy. Plasmodium falciparum gametocyte carriage is subclinical, but gametocytemic individuals comprise the parasite reservoir that leads to infection of mosquitoes and local transmission. Effective detection and quantification of these carriers can help advance malaria elimination strategies. However, no point-of-need (PON) RDTs for gametocyte detection exist, much less one that can perform noninvasive sampling of saliva outside a clinical setting. Here, we report on the discovery of 35 parasite markers from which we selected a single candidate for use in a PON RDT. We performed a cross-sectional, multi-omics study of saliva from 364 children with subclinical infection in Cameroon and Zambia and produced a prototype saliva-based PON lateral flow immunoassay test for P. falciparum gametocyte carriers. The test is capable of identifying submicroscopic carriage in both clinical and nonclinical settings and is compatible with archived saliva samples.

Highlights

Malaria kills ~500,000 children each year, mostly children under the age of 5 in sub-Saharan Africa [1]
The proteins can be divided into several classes, including cytosolic “housekeeping” proteins that are conserved between asexual and gametocyte stages of P. falciparum [20], and those that are specific to asexual stages alone [21, 22]
Of the 35 proteins that we detected in pooled saliva from the children, PF3D7_1218800 was the most abundant in individual saliva samples from children who were found to be gametocyte positive by blood film microscopy (Mascot ions scores; Table 1 and table S2)

Summary

Introduction

Malaria kills ~500,000 children each year, mostly children under the age of 5 in sub-Saharan Africa [1]. Low-density subclinical infection with Plasmodium falciparum among defined population subsets has been shown to be an important but cryptic facet of malaria transmission These individuals are not readily detected by currently available point-of-need (PON) rapid diagnostic tests (RDTs) or microscopy [2,3,4,5], and molecular methods not readily available to hospitals, clinics, or other PON sites such as households, schools, or apothecaries are required for detection and quantification of parasite carriage. In response to the growing concern that parasites lacking the pfhrp2/pfhrp genes are resulting in false-negative HRP2-RDT results and children being left untreated, the World Health Organization (WHO) has encouraged the scientific community to identify new target biomarkers of the parasite that allow for the sensitive detection of carriage [12] To address this critical scientific gap and obstacle to malaria elimination and eradication, we developed a noninvasive diagnostic amenable for epidemiological surveillance programs and mass screening campaigns, both of which go beyond the limitation of a clinical setting

Objectives

Methods

Results

Conclusion