Malaria species positivity rates among symptomatic individuals across regions of differing transmission intensities in Mainland Tanzania

Abstract

Recent data indicate that non-Plasmodium falciparum species may be more prevalent than previously realized in sub-Saharan Africa, the region where 95% of the world's malaria cases occur. Although Plasmodium malariae, Plasmodium ovale spp., and Plasmodium vivax are generally less severe than P. falciparum, treatment and control are more challenging, and their geographic distributions are not well characterized. In order to characterize the distribution of malaria species in Mainland Tanzania (which has a high burden and geographically heterogeneous transmission levels), we randomly selected 3,284 samples from 12,845 samples to determine presence and parasitemia of different malaria species. The samples were collected from cross-sectional surveys in 100 health facilities across ten regions and analyzed via quantitative real-time PCR to characterize regional positivity rates for each species. P. falciparum was most prevalent, but P. malariae and P. ovale were found in all regions except Dar es Salaam, with high levels (>5%) of P. ovale in seven regions (70%). The highest positivity rate of P. malariae was 4.5% in Mara region and eight regions (80%) had positivity rates ≥1%. We also detected three P. vivax infections in the very low-transmission Kilimanjaro region. While most samples that tested positive for non-falciparum malaria were co-infected with P. falciparum, 23.6% (n = 13/55) of P. malariae and 14.7% (n = 24/163) of P. ovale spp. samples were mono-infections. P. falciparum remains by far the largest threat, but our data indicate that malaria elimination efforts in Tanzania will require increased surveillance and improved understanding of the biology of non-falciparum species.

Malaria species prevalence among asymptomatic individuals in four regions of Mainland Tanzania

“…prevalence (24%) was similar to that of P. falciparum (22%) [6], while in symptomatic patients, P. falciparum was much more abundant than non-falciparum malaria, although P. ovale spp. positivity rates surpassed 5% in seven of ten regions [12]. In both studies, P. malariae was less common than either P. falciparum or P. ovale spp., and P. vivax was rare [6,12].…”

“…positivity rates surpassed 5% in seven of ten regions [12]. In both studies, P. malariae was less common than either P. falciparum or P. ovale spp., and P. vivax was rare [6,12]. In this study, we characterize the prevalence of all malaria species among asymptomatic individuals across all ages in three regions with moderate and high malaria transmission intensity, and in children under five in one region with high transmission.…”

“…Previous work in Mainland Tanzania has characterized non-falciparum prevalence in schoolchildren (5-16 years) [6] and non-falciparum positivity rates among symptomatic patients [12]. In schoolchildren, P. ovale spp.…”

“…The molecular analyses used to detect Plasmodium spp. in each sample are described in detail elsewhere [12]. Briefly, we performed a separate 18S qPCR assay for each species, which allows for both the detection of each species as well as a semi-quantitative parasitemia estimate.…”

“…Variation in species-specific prevalence by region and age group (young children <5 years, school-aged children 5-16 years, and adults >16 years, as previously described [12]) was assessed for significance with generalized linear models or ANOVA, as appropriate, in R.…”