Background: Malaria is a mosquito borne disease caused by parasites of the genus Plasmodium. In 2023, the United States (US) experienced nine cases of autochthonous Plasmodium vivax malaria transmission; seven in Florida, one in Texas, and another in Arkansas. These were the first autochthonous cases since 2003 when a cluster was identified in Florida. The aim of this study was to genetically characterize the implicated P. vivax isolates in order to complement epidemiologic investigations of these cases. Methods: A custom Illumina AmpliSeq sequencing panel capturing 495 amplicons was designed. This panel was used to ascertain whether these 2023 cases were related, and assess if they were associated with a single or separate introduction events. Sequence data were hierarchically clustered and a Naïve Bayes classification approach was used to assign genotypes to a probable geographic origin based on 113 ‘geo-informative’ SNPs captured by the panel. Genotypes associated with the 2023 Arkansas, Texas, and Florida cases were clustered alongside those sequenced from archived blood samples from the 2003 Florida case-patients, a set of reference strains, and other travel-associated specimens. Microsatellite analysis was performed on a subset of samples from these autochthonous cases to complement the AmpliSeq analysis. Findings: The 2023 autochthonous Florida cases were genetically linked as were the 2003 Florida cases. The 2023 and 2003 Florida clusters were genetically distinct, and the two Florida clusters were distinct from the 2023 Texas and Arkansas cases, which were also distinct from each other. These genotypes classified to the Central or South American region using the Naïve Bayes classifier, including those from the 2003 cluster. Interpretation: These data support that at least three distinct P. vivax introduction events in the US in 2023, involving parasites possessing genetic signatures consistent with Central or South America. Funding: This work was supported by the National Center for Emerging and Zoonotic Infectious Diseases at the US Centers for Disease Control and Prevention. © 2025

BACKGROUND: Artemether-lumefantrine (AL) is the first line anti-malarial drug for the treatment of uncomplicated malaria in Tanzania. The World Health Organization (WHO) recommends regular efficacy monitoring of anti-malarial drugs to inform case management policy decisions. This study assessed the safety and efficacy of AL for treating uncomplicated P. falciparum malaria in Tanzania in 2022. METHODS: Children 6 months to 10 years with uncomplicated P. falciparum malaria were recruited from four sentinel sites and treated with the standard 6 dose, 3-day regimen for AL. Clinical and parasitological responses were monitored for 28 days using the WHO standard protocol. Genotyping based on msp1, msp2 and glurp was used to distinguish recrudescence from reinfection. SANGER sequencing was used to detect K13 mutations. RESULTS: 352 participants, 88 per site, were enrolled. Four withdrew and 55 experienced parasite recurrence. The PCR corrected Kaplan-Meier efficacies were, 89.9% in Pwani, 95.0% in Kigoma, 94.4% in Tanga, and 98.9% in Morogoro. No K13 mutations were found. CONCLUSIONS: Artemether-lumefantrine remains highly efficacious in three regions of Tanzania but the PCR-corrected efficacy in Pwani fell below the WHO-defined 90% threshold at which policy change is recommended. Implementing strategies to diversify ACTs to ensure effective case management in Tanzania is critical.

Naturally occurring human infections by zoonotic Plasmodium species have been documented for P. knowlesi, P. cynomolgi, P. simium, P. simiovale, P. inui, P. inui-like, P. coatneyi, and P. brasilianum. Accurate detection of each species is complicated by their morphological similarities with other Plasmodium species. PCR-based assays offer a solution but require prior knowledge of adequate genomic targets that can distinguish the species. While whole genomes have been published for P. knowlesi, P. cynomolgi, P. simium, and P. inui, no complete genome for P. brasilianum has been available. Previously, we reported a draft genome for P. brasilianum, and here we report the completed genome for P. brasilianum. The genome is 31.4 Mb in size and comprises 14 chromosomes, the mitochondrial genome, the apicoplast genome, and 29 unplaced contigs. The chromosomes consist of 98.4% nucleotide sites that are identical to the P. malariae genome, the closest evolutionarily related species hypothesized to be the same species as P. brasilianum, with 41,125 non-synonymous SNPs (0.0722% of genome) identified between the two genomes. Furthermore, P. brasilianum had 4864 (82.1%) genes that share 80% or higher sequence similarity with 4970 (75.5%) P. malariae genes. This was demonstrated by the nearly identical genomic organization and multiple sequence alignments for the merozoite surface proteins msp3 and msp7. We observed a distinction in the repeat lengths of the circumsporozoite protein (CSP) gene sequences between P. brasilianum and P. malariae. Our results demonstrate a 97.3% pairwise identity between the P. brasilianum and the P. malariae genomes. These findings highlight the phylogenetic proximity of these two species, suggesting that P. malariae and P. brasilianum are strains of the same species, but this could not be fully evaluated with only a single genomic sequence for each species.