New assay detects subclinical infection of malaria parasite

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The gametocyte sexual form of Plasmodium falciparum, a parasite that causes human malaria, is responsible for mosquito-borne transmission of infection. Some individuals carry low concentrations of the parasite (subclinical infection), which makes detection and eradication difficult.

A team of international researchers led by Rhoel R Dinglasan at the Johns Hopkins Bloomberg School of Public Health, the Johns Hopkins Malaria Research Institute and the Emerging Pathogens Institute and department of infectious diseases & immunology, College of Veterinary Medicine, University of Florida, Gainesville developed a rapid lateral flow assay that detects a female gametocyte-specific protein, PSSP17, in saliva.

Compared to standard molecular and microscopic analyses of matched blood samples, the rapid diagnostic assay could detect sub-microscopic parasite carriage in saliva from children and adults in Cameroon, Zambia and Sierra Leone in clinical and nonclinical settings.

The researchers say this assay could help identify individuals with subclinical P. falciparum infections to reduce the infectious reservoir.

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 non-invasive 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 sub-microscopic carriage in both clinical and nonclinical settings and is compatible with archived saliva samples.

Authors
Dingyin Tao, Brent McGill, Timothy Hamerly, Tamaki Kobayashi2, Prachi Khare, Amanda Dziedzic, Tomasz Leski, Andrew Holtz, Bruce Shull, Anne E Jedlicka, Andrew Walzer, Paul D Slowey, Christopher C Slowey, Sandrine E Nsango, David A Stenger, Mike Chaponda, Modest Mulenga, Kathryn H Jacobsen, David J Sullivan, Sadie J Ryan, Rashid Ansumana, William J Moss, Isabelle Morlais, Rhoel R Dinglasan

Science Translational Medicine abstract

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