The Merits of Malaria Diagnostics during an Ebola Virus Disease Outbreak

Abstract

Malaria is a major public health concern in the countries affected by the Ebola virus disease epidemic in West Africa. We determined the feasibility of using molecular malaria diagnostics during an Ebola virus disease outbreak and report the incidence of Plasmodium spp. parasitemia in persons with suspected Ebola virus infection.

Keywords: Ebola; Ebola virus; Ebola virus disease; Guinea; Liberia; PCR; Plasmodium; Sierra Leone; West Africa; diagnostics; disease outbreak; malaria; public health; viruses.

Figure 1

Prevalence of Ebola virus (EBOV) and Plasmodium spp. RNA in patient samples submitted to the Centers for Disease Control and Prevention–National Institutes of Health diagnostic laboratory at the Eternal Love Winning Africa campus in Monrovia, Liberia, from October 12, 2014 (epidemiologic week 42), through March 28, 2015 (week 13). Whole blood samples were inactivated, and RNA was extracted by using the QIAAmp Viral RNA Mini Kit (QIAGEN, Hilden, Germany). These samples were then tested for the presence of EBOV RNA and Plasmodium spp. RNA by real-time quantitative reverse transcription PCR (qRT-PCR) (13). A) Number of patients, as determined by qRT-PCR, positive for EBOV, Plasmodium spp., both, or neither (i.e., no EBOV and no Plasmodium spp.), by epidemiologic week. B) Total number of patients receiving a laboratory diagnosis of Ebola viremia, Plasmodium spp. parasitemia, both, or neither. C) A subset of 311 Plasmodium spp. qRT-PCR–positive samples that were retested with a qRT-PCR specific for P. falciparum (14).

Figure 2

Inverse parasite load in patients with Plasmodium spp. parasitemia over time by month of sample submission, for samples submitted to the Centers for Disease Control and Prevention–National Institutes of Health diagnostic laboratory at the Eternal Love Winning Africa campus in Monrovia, Liberia, from October 12, 2014, through March 28, 2015. Cycle threshold (C_t) values were detected by using real-time quantitative reverse transcription PCR. Triangles represent parasite loads in parasitemic patients co-infected with Ebola virus; circles represent patients with Plasmodium spp. parasitemia only. In West Africa, similar to other malaria-endemic regions, a large proportion of the population is infected with Plasmodium parasites without developing clinical disease. To compensate for this and the higher sensitivity of the PCR assay compared with light microscopy, we used a cutoff of C_t <30 rather than C_t <40 under the assumption that a 10-C_t difference would compensate for the ≈1,000-fold higher sensitivity of PCR over microscopy. This principle could be carried further to assume that a C_t <25 would be in the range detectable by the rapid diagnostic test. Of note, high C_t values correspond to low parasitemia levels and vice versa.