Similar Prevalence of Plasmodium falciparum and Non-P. falciparum Malaria Infections among Schoolchildren, Tanzania1

Abstract

Achieving malaria elimination requires considering both Plasmodium falciparum and non-P. falciparum infections. We determined prevalence and geographic distribution of 4 Plasmodium spp. by performing PCR on dried blood spots collected within 8 regions of Tanzania during 2017. Among 3,456 schoolchildren, 22% had P. falciparum, 24% had P. ovale spp., 4% had P. malariae, and 0.3% had P. vivax infections. Most (91%) schoolchildren with P. ovale infections had low parasite densities; 64% of P. ovale infections were single-species infections, and 35% of those were detected in low malaria endemic regions. P. malariae infections were predominantly (73%) co-infections with P. falciparum. P. vivax was detected mostly in northern and eastern regions. Co-infections with >1 non-P. falciparum species occurred in 43% of P. falciparum infections. A high prevalence of P. ovale infections exists among schoolchildren in Tanzania, underscoring the need for detection and treatment strategies that target non-P. falciparum species.

Keywords: PCR; Plasmodium falciparum; Plasmodium malariae; Plasmodium ovale; Plasmodium vivax; Tanzania; children; epidemiology; malaria; parasites; school survey; vector-borne infections; zoonoses.

Figure 6

Equation.

Figure 1

Distribution of Plasmodium spp. infections among schoolchildren, Tanzania. Prevalence estimates according to species: P. falciparum, 21.8% (95% CI 20.5%–23.3%, n = 755); P. ovale, 23.6% (95% CI 22.2%–25.0%, n = 814); P. malariae, 3.9% (95% CI 3.3%–4.6%, n = 136); P. vivax: 0.3% (95% CI 0.2%–0.6%, n = 11). P. vivax + P. malariae co-infection (n = 1) is not shown.

Figure 2

Estimated parasite density distributions according to malaria species in study of similar prevalence of Plasmodium falciparum and non–P. falciparum malaria infections among schoolchildren, Tanzania. We estimated Plasmodium spp. parasite densities for single infections and co-infections (mixed) by using semiquantitative PCR and species-specific primers (Appendix Table 1). Mixed infections included P. falciparum and nonfalciparum co-infections. Number of samples varied by species. P. ovale and P. vivax parasite densities were detected by using 45 PCR cycles; other species were determined by using 40 PCR cycles. A) P. falciparum: median (IQR) density was 11.4 (2.5–54.7) parasites/µL for single-species infections (n = 429) and 16.5 (3.5–56.9) parasites/µL for mixed-species infections (n = 326) (p = 0.117). B) P. ovale: median (IQR) density was 13.5 (1.3–30.1) parasites/µL for single-species infections (n = 519) and 3.1 (1.2–11.4) parasites/µL for mixed-species infections (n = 295) (p<0.001). C) P. malariae: median (IQR) density was 16.1 (3.8–164.0) parasites/µL for single-species infections (n = 24) and 11.2 (2.6–53.9) parasites/µL for mixed-species infections ([n = 112) (p = 0.169). D) P. vivax: median (IQR) density was 0.4 (0.2–0.9) parasites/µL for single-species infections (n = 4) and 0.7 (0.5–0.8) parasites/µL for mixed-species infections (n = 7) (p = 0.571). IQR, interquartile range.

Figure 3

Locations of 8 survey regions within mainland Tanzania (dark gray shading) in study of similar prevalence of Plasmodium falciparum and non–P. falciparum malaria infections among schoolchildren, Tanzania.

Figure 4

Spatial distribution of regional and school council–level malaria prevalence by species in study of similar prevalence of Plasmodium falciparum and non–P. falciparum malaria infections among schoolchildren, Tanzania. A) P. falciparum; B) P. ovale; C) P. malariae; D) P. vivax.

Figure 5

Differential scaled prevalences between Plasmodium malariae or P. ovale and P. falciparum at the school council level in study of similar prevalence of Plasmodium falciparum and non–P. falciparum malaria infections among schoolchildren, Tanzania. A) Blue shading indicates councils where P. falciparum scaled prevalence is greater (indicated by + in key) than P. malariae scaled prevalence; gold indicates regions where P. malariae scaled prevalence is greater. B) Light blue shading indicates councils where P. falciparum scaled prevalence is greater than P. ovale spp. scaled prevalence; green indicates regions where P. ovale scaled prevalence is greater. Comparison of scaled prevalences for P. falciparum and P. vivax is not depicted because the low number of P. vivax infections biased the scaled measurement.