Molecular typing exposes a hidden non-falciparum malaria burden in Chad
In the Sudano-Sahelian region of Chad, malaria did not present as a single-pathogen story. A community-based survey using rapid diagnostic testing, microscopy, and PCR found a much wider spectrum of infection than routine field methods were able to capture, with Plasmodium detected in 57.6% of 601 blood samples by PCR, compared with 28.1% by microscopy and 23.6% by rapid diagnostic testing. The gap between molecular detection and conventional diagnosis was large enough to matter clinically and operationally. It means a substantial reservoir of infections can remain invisible in asymptomatic people while transmission continues.
The cohort was collected between November 2024 and January 2025, a period that fits the seasonal transmission profile of the region. Among PCR-positive infections, P. falciparum mono-infection remained the dominant pattern at 58.1% of 346 infected samples. Even so, non-falciparum species were clearly present, including sub-patent P. malariae mono-infection in 2.6% and P. ovale species in 2.0%. Mixed infections were common enough to reshape the local epidemiology: P. falciparum/P. malariae accounted for 11.3%, P. falciparum/P. ovale for 17.6%, P. malariae/P. ovale for 3.2%, and triple infections involving all three species for 5.2%.
Silent infection is not benign when hemoglobin is falling.
Anemia tracked with parasite detection, not symptoms
The most clinically consequential finding was the hemoglobin gradient. People with PCR-detected malaria had a mean hemoglobin of 9.58 ± 1.40 g/dL, compared with 12.6 ± 1.29 g/dL in those without detectable infection. The mean difference was −2.29 g/dL, with a 95% confidence interval from −2.51 to −2.08 and a p value below 0.001. In practical terms, a community sample that appeared largely asymptomatic still carried a measurable burden of anemia.
This pattern fits malaria biology. Even in the absence of fever or overt illness, chronic or repeated parasitemia can impair red cell survival, suppress erythropoiesis, and contribute to iron-restricted hematologic recovery. Non-falciparum infections deserve particular attention here because they are easy to miss and can persist at low density. When they circulate alongside P. falciparum, they may extend the duration of exposure rather than announcing themselves with acute illness.
A separate analysis linked non-falciparum infections, including P. malariae and P. ovale mono-infections and P. malariae plus P. ovale co-infections, with moderate anemia. The reported hemoglobin level in that group was 9.3 g/dL, and the odds ratio for moderate anemia was 3.4, with a 95% confidence interval of 1.6 to 7.2 and a p value of 0.03. Even though these species often receive less clinical attention than P. falciparum, the hematologic signal suggests they carry real morbidity in endemic communities.
Age patterns point to missed exposure in school-age children and older adults
Mixed-species infections were concentrated in the 6–15 year and over-40 age groups, with an odds ratio of 7.3 and a 95% confidence interval of 4.1 to 11.5; the p value was 0.004. This age clustering is important because it points to population segments that may be sustaining transmission outside the most heavily targeted prevention strata. School-age children often sit in the epidemiologic blind spot between routine pediatric care and adult screening. Older adults, meanwhile, may not be prioritized for malaria testing unless they are overtly symptomatic.
The result also suggests that local control programs built around visible illness will miss a substantial part of the reservoir. Asymptomatic carriage in these age bands can preserve transmission despite intensive deployment of malaria control interventions. The study setting already had broad intervention coverage, yet PCR still identified more than half the sampled population as infected. That mismatch between intervention intensity and residual infection burden is a warning sign for elimination campaigns that rely too heavily on symptomatic case detection.
Species typing reveals local transmission of sibling lineages and probable cross-border relatedness
Beyond prevalence and anemia, molecular characterization added another layer to the story. The study identified both P. ovale curtisi and P. ovale wallikeri among local infections, with 36 of 70 typed isolates corresponding to P. ovale curtisi and 19 of 70 to P. ovale wallikeri. These sibling subspecies matter because they are easily overlooked in routine diagnostics and signal that the non-falciparum component of malaria is biologically diverse, not a single residual category.
Sequence analysis of the merozoite surface protein-1 gene from nine local P. malariae isolates suggested low genetic diversity, with nucleotide diversity of π = 0.002 and haplotype diversity of Hd = 0.72. The isolates also appeared phylogenetically close to a historical Cameroon reference strain, implying geographical relatedness with possible implications for cross-border malaria control. In a region where borders are porous and human movement is routine, parasite flow does not stop at administrative lines.
Malaria elimination in Chad will have to reach beyond P. falciparum
The public health message is straightforward even if the biology is not: a malaria program focused almost exclusively on P. falciparum will leave part of the parasite burden untreated and unmeasured. Molecular diagnostics exposed sub-microscopic infections that conventional approaches missed, and those hidden infections were linked to lower hemoglobin and moderate anemia. The burden was not evenly distributed, either. Mixed infections clustered in specific age groups, and non-falciparum parasites carried a measurable hematologic cost.
For the Chad National Malaria Control Programme, the study argues for a broader surveillance strategy that includes all relevant malaria species, not only the dominant one. PCR-based species typing is not likely to become a universal frontline test in every setting, but the data make a strong case for periodic molecular surveillance, especially where elimination goals depend on finding the last reservoirs of transmission. Diagnostic algorithms, treatment policy, and cross-border coordination all become more urgent when silent infections remain common.
The current study was cross-sectional, so it cannot establish how long these infections persisted or how much each species contributed separately to anemia over time. Even so, the hemoglobin deficit, the mixed-species burden, and the species-level diversity together point to a malaria ecology that routine surveillance is still undercounting.