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New rapid molecular tool reveals parasites that escape malaria tests

A new study conducted by researchers from the London School of Hygiene & Tropical Medicine, in collaboration with international partners, shows the development of a rapid quantitative PCR to detect Plasmodium falciparum parasites – the deadliest form of parasites causing malaria, that evade rapid diagnostic tests (RDT). The new molecular tool, described in EBioMedicine, a journal published by The Lancet, could significantly improve the surveillance efforts of such parasites to guide RDT procurement and avert a serious public health threat.

Current detection methods require several individual PCR reactions to detect the parasites that evade RDTs. The new rapid quantitative test is a multiplex assay, which targets three parasite genes and one human beta tubulin gene (HumTuBB) in a sole PCR reaction. This will save time for researchers.

The three parasite genes are Plasmodium falciaprum lactate dehydrogenase (pfldh) as well as P. falciparum histidien-rich protein 2 and 3 (pfhrp2 and pfhrp3). Pfhrp2 and pfhrp3 are genes that encode the protein antigens commonly recognised by the RDTs. Plasmodium parasites that evade RDTs have been reported in South America, Africa and India. The emergence of such parasites threatens the utility of hrp2-based RDTs as a diagnostic test and impacts control and elimination programs, if malaria is undetectable. 

The study, which analysed blood samples from 462 malaria patients in three different studies (including 113 from UK travellers obtained from the Malaria Reference Laboratory) found that the new tool can rapidly and accurately detect the deletions. The study reports, for the first time, the presence of such parasites in UK travellers from Somalia and South Sudan, and it also confirms the presence of the deletion in Eritrea, Ethiopia, Kenya, Sudan and Uganda. The findings have implication for malaria diagnosis in the UK.

Dr. Khalid Beshir, Assistant Professor in the Faculty of Infectious and Tropical Diseases (ITD) at LSHTM, said “The existing genetic tools employed to identify the parasites with the deletions are time-consuming and often not reliable. We hope that this new quantitative molecular tool will overcome the limitations and provide accurate and rapid support for surveillance of malaria parasites with the gene deletions”.

Dr. Lynn Grignard, Research Fellow in the Faculty of ITD at LSHTM, added “Having a single, multi-target assay at our disposal reduces the time required to get results from days to hours”.

Read the full paper here.

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