Malaria Parasite Evades Rapid Test Detection in Children

Rapid diagnostic tests account for more than 70% of diagnostic testing for malaria in Africa and most rapid test diagnostics rely on the detection an antigen specific to Plasmodium falciparum malaria.

The Democratic Republic of the Congo (DRC) has one of the highest rates of people living with malaria. Most rapid test diagnostics (RDT) rely on the detection of histidine-rich protein 2 (HRP2), an antigen specific to P. falciparum malaria. However, one of every 15 children infected with P. falciparum malaria parasites in the DRC is infected by a pfhrp2-deleted mutant, producing a false-negative result when an RDT is used.

An international team of scientists led by those at University of North Carolina Health Care System (Chapel Hill, NC, USA) collected samples from children under five years of age as part of the 2013- 2014 DRC Demographic and Health Survey. The majority of children were asymptomatic at the time of sample collection. Heel- or finger-prick blood from each participant was analyzed by light microscopy for parasites, applied to an RDT targeting the P. falciparum HRP2 antigen.

The samples were applied to an RDT targeting the P. falciparum HRP2 antigen (SD BIOLINE Malaria Ag P.f., Standard Diagnostics, Gyeonggi-do, Republic of Korea), and used to prepare dried blood spots (DBS). Three diagnostic methods were performed for each child: RDT, microscopy, and polymerase chain reaction (PCR). The real-time PCR assay with a limit of detection of 100 parasites/μL was employed to identify P. falciparum infection by amplifying a region of the single-copy pfldh gene.

The team focused on 783 samples with opposing rapid test diagnostic test and polymerase chain reaction (PCR) results. PCR testing showed positive results for malaria where rapid diagnostic testing did not. They identified 149 pfhrp2-deleted parasites, representing 6.4% of all P. falciparum infections country-wide among the 2,752 children diagnosed with P. falciparum infection by real-time PCR and 19.0 % of the 783 RDT-/PCR+ parasites tested.

Jonathan Parr, MD. MPH. the study's lead author, said, “This is the first nationwide study to demonstrate the presence and estimate the prevalence of malaria caused by pfhrp2-deleted P. falciparum in asymptomatic children. Because most rapid diagnostic tests in the DRC are HRP2-based, they will fail to detect these parasites. Their spread would represent a serious threat to malaria elimination efforts.” The study was published on November 14, 2016, in the Journal of Infectious Diseases.

Related Links:
University of North Carolina Health Care System
Standard Diagnostics