Seroprevalence and Parasite Rates of Plasmodium malariae in a High Malaria Transmission Setting of Southern Nigeria

Abstract

Although Plasmodium falciparum continues to be the main target for malaria elimination, other Plasmodium species persist in Africa. Their clinical diagnosis is uncommon, whereas rapid diagnostic tests (RDTs), the most widely used malaria diagnostic tools, are only able to distinguish between P. falciparum and non-falciparum species, the latter as "pan-species." Blood samples from health facilities were collected in southern Nigeria (Lagos and Calabar) in 2017 (October-December) and Calabar only in 2018 (October-November), and analyzed by several methods, namely, microscopy, quantitative real-time PCR (qPCR), and peptide serology targeting candidate antigens (Plasmodium malariae apical membrane antigen, P. malariae lactose dehydrogenase, and P. malariae circumsporozoite surface protein). Both microscopy and qPCR diagnostic approaches detected comparable proportions (∼80%) of all RDT-positive samples infected with the dominant P. falciparum malaria parasite. However, higher proportions of non-falciparum species were detected by qPCR than microscopy, 10% against 3% infections for P. malariae and 3% against 0% for Plasmodium ovale, respectively. No Plasmodium vivax infection was detected. Infection rates for P. malariae varied between age-groups, with the highest rates in individuals aged > 5 years. Plasmodium malariae-specific seroprevalence rates fluctuated in those aged < 10 years but generally reached the peak around 20 years of age for all peptides. The heterogeneity and rates of these non-falciparum species call for increased specific diagnosis and targeting by elimination strategies.

Figure 1.

Map of study sites in Nigeria showing (A) Lagos (southwest zone) and Cross River (south–south zone) states; and (B) health facilities in Cross River state, where participants were recruited. This figure appears in color at www.ajtmh.org.

Figure 2.

Summary of diagnostic results. (A) Prevalence of malaria in both surveys by RDTs. (B) Proportion of Plasmodium species detected by qPCR and microscopy in RDT-positive samples from the first survey. Mx_Pf = P. falciparum detected by microscopy; Mx_Pm = P. malariae detected by microscopy; qPCR = quantitative real-time PCR; qPCR_Pf = P. falciparum detected by qPCR; qPCR_Pm = P. malariae detected by qPCR; qPCR_Po = P. ovale detected by qPCR; qPCR_Pv = P. vivax detected by qPCR. RDT = rapid diagnostic test. This figure appears in color at www.ajtmh.org.

Figure 3.

Proportion of Plasmodium species detected in the four villages in southeastern Nigeria, detected by quantitative real-time PCR (qPCR) (qPCR_Pf = P. falciparum; qPCR_Pm = P. malariae; qPCR_Po = P. ovale). This figure appears in color at www.ajtmh.org.

Figure 4.

Area under the receiver operator curve (ROC) showing comparison of fold over the negative control for each of the peptides with rapid diagnostic test (RDT) and microscopy results. This figure appears in color at www.ajtmh.org.

Figure 5.

Seroprevalence rates of the different species-specific peptides in different age-groups; the slope is the estimated change of rate over age-group. This figure appears in color at www.ajtmh.org.