Evolution of Spatial Risk of Malaria Infection After a Pragmatic Chemoprevention Program in Response to Severe Flooding in Rural Western Uganda.

BACKGROUND: Malaria epidemics result from extreme precipitation and flooding, which are increasing with global climate change. Local adaptation and mitigation strategies will be essential to prevent excess morbidity and mortality. METHODS: We investigated the spatial risk of malaria infection at multiple timepoints after severe flooding in rural western Uganda employing longitudinal household surveys measuring parasite prevalence and leveraging remotely sensed information to inform spatial models of malaria risk in the 3 months after flooding. RESULTS: We identified clusters of malaria risk emerging in areas (1) that showed the greatest changes in Normalized Difference Vegetation Index from pre- to postflood and (2) where residents were displaced for longer periods of time and had lower access to long-lasting insecticidal nets, both of which were associated with a positive malaria rapid diagnostic test result. The disproportionate risk persisted despite a concurrent chemoprevention program that achieved high coverage. CONCLUSIONS: The findings enhance our understanding not only of the spatial evolution of malaria risk after flooding, but also in the context of an effective intervention. The results provide a "proof of concept" for programs aiming to prevent malaria outbreaks after flooding using a combination of interventions. Further study of mitigation strategies-and particularly studies of implementation-is urgently needed.

Adjuvant therapy may improve overall survival in high-risk periampullary adenocarcinomas patients - A match-pair analysis from a multi-institutional cohort study (The MIPPAP study).

BACKGROUND: The role of adjuvant therapy in resected periampullary adenocarcinomas is equivocal due to contrasting data and limited prospective trials. METHODS: The Multicentre Indian Pancreatic & Periampullary Adenocarcinoma Project (MIPPAP), included data from 8 institutions across India. Of the 1679 pancreatic resections, 736 patients with T3/T4 and/or Node positive adenocarcinomas (considered as high risk for recurrence) were included for analysis. Three (adjuvant): one (observation) matching, using T3/T4 T staging, nodal positivity and ampullary subtype was performed by using the nearest neighbour matching method. RESULTS: Of 736 patients eligible for inclusion, 621 patients were matched of which 458 patients received adjuvant therapy (AT) (predominantly gemcitabine-based) and 163 patients were observed (O). With a median follow-up of 42 months, there was a statistical difference in overall survival in favour of patients receiving AT as compared to those on observation [68.7 months vs. 61.1 months, Hazard ratio: 0.73 (95% CI: 0.54-0.97); p = 0.03]. Besides AT, presence of nodal involvement (median OS: 65.4 months vs not reached; p = 0.04) predicted for inferior OS. CONCLUSIONS: The results of the match-pair analysis suggest that adjuvant therapy improves overall survival in periampullary adenocarcinomas at high risk of recurrence with a greater benefit in T3/T4, node-positive and ampullary subtypes.

Background malaria incidence and parasitemia during the three-dose RTS,S/AS01 vaccination series do not reduce magnitude of antibody response nor efficacy against the first case of malaria.

BACKGROUND: RTS,S/AS01 has been recommended by WHO for widespread implementation in medium to high malaria transmission settings. Previous analyses have noted lower vaccine efficacies in higher transmission settings, possibly due to the more rapid development of naturally acquired immunity in the control group. METHODS: To investigate a reduced immune response to vaccination as a potential mechanism behind lower efficacy in high transmission areas, we examine initial vaccine antibody (anti-CSP IgG) response and vaccine efficacy against the first case of malaria (to exclude the effect of naturally acquired immunity) using data from three study areas (Kintampo, Ghana; Lilongwe, Malawi; Lambaréné, Gabon) from the 2009-2014 phase III trial (NCT00866619). Our key exposures are parasitemia during the vaccination series and background malaria incidence. We calculate vaccine efficacy (one minus hazard ratio) using a cox-proportional hazards model and allowing for the time-varying effect of RTS,S/AS01. RESULTS: We find that antibody responses to the primary three-dose vaccination series were higher in Ghana than in Malawi and Gabon, but that neither antibody levels nor vaccine efficacy against the first case of malaria varied by background incidence or parasitemia during the primary vaccination series. CONCLUSIONS: We find that vaccine efficacy is unrelated to infections during vaccination. Contributing to a conflicting literature, our results suggest that vaccine efficacy is also unrelated to infections before vaccination, meaning that control-group immunity is likely a major reason for lower efficacy in high transmission settings, not reduced immune responses to RTS,S/AS01. This may be reassuring for implementation in high transmission settings, though further studies are needed.

An artificial intelligence model that automatically labels roux-en-Y gastric bypasses, a comparison to trained surgeon annotators.

INTRODUCTION: Artificial intelligence (AI) can automate certain tasks to improve data collection. Models have been created to annotate the steps of Roux-en-Y Gastric Bypass (RYGB). However, model performance has not been compared with individual surgeon annotator performance. We developed a model that automatically labels RYGB steps and compares its performance to surgeons. METHODS AND PROCEDURES: 545 videos (17 surgeons) of laparoscopic RYGB procedures were collected. An annotation guide (12 steps, 52 tasks) was developed. Steps were annotated by 11 surgeons. Each video was annotated by two surgeons and a third reconciled the differences. A convolutional AI model was trained to identify steps and compared with manual annotation. For modeling, we used 390 videos for training, 95 for validation, and 60 for testing. The performance comparison between AI model versus manual annotation was performed using ANOVA (Analysis of Variance) in a subset of 60 testing videos. We assessed the performance of the model at each step and poor performance was defined (F1-score < 80%). RESULTS: The convolutional model identified 12 steps in the RYGB architecture. Model performance varied at each step [F1 > 90% for 7, and > 80% for 2]. The reconciled manual annotation data (F1 > 80% for > 5 steps) performed better than trainee's (F1 > 80% for 2-5 steps for 4 annotators, and < 2 steps for 4 annotators). In testing subset, certain steps had low performance, indicating potential ambiguities in surgical landmarks. Additionally, some videos were easier to annotate than others, suggesting variability. After controlling for variability, the AI algorithm was comparable to the manual (p < 0.0001). CONCLUSION: AI can be used to identify surgical landmarks in RYGB comparable to the manual process. AI was more accurate to recognize some landmarks more accurately than surgeons. This technology has the potential to improve surgical training by assessing the learning curves of surgeons at scale.

Malaria Transmission Intensity Likely Modifies RTS, S/AS01 Efficacy Due to a Rebound Effect in Ghana, Malawi, and Gabon.

BACKGROUND: RTS,S/AS01 is the first malaria vaccine to be approved and recommended for widespread implementation by the World Health Organization (WHO). Trials reported lower vaccine efficacies in higher-incidence sites, potentially due to a "rebound" in malaria cases in vaccinated children. When naturally acquired protection in the control group rises and vaccine protection in the vaccinated wanes concurrently, malaria incidence can become greater in the vaccinated than in the control group, resulting in negative vaccine efficacies. METHODS: Using data from the 2009-2014 phase III trial (NCT00866619) in Lilongwe, Malawi; Kintampo, Ghana; and Lambaréné, Gabon, we evaluate this hypothesis by estimating malaria incidence in each vaccine group over time and in varying transmission settings. After estimating transmission intensities using ecological variables, we fit models with 3-way interactions between vaccination, time, and transmission intensity. RESULTS: Over time, incidence decreased in the control group and increased in the vaccine group. Three-dose efficacy in the lowest-transmission-intensity group (0.25 cases per person-year [CPPY]) decreased from 88.2% to 15.0% over 4.5 years, compared with 81.6% to -27.7% in the highest-transmission-intensity group (3 CPPY). CONCLUSIONS: These findings suggest that interventions, including the fourth RTS,S dose, that protect vaccinated individuals during the potential rebound period should be implemented for high-transmission settings.

Dihydroartemisinin-Piperaquine Chemoprevention and Malaria Incidence After Severe Flooding: Evaluation of a Pragmatic Intervention in Rural Uganda.

BACKGROUND: Malaria epidemics are a well-described phenomenon after extreme precipitation and flooding. Yet, few studies have examined mitigation measures to prevent post-flood malaria epidemics. METHODS: We evaluated a malaria chemoprevention program implemented in response to severe flooding in western Uganda. Children aged ≤12 years from 1 village were eligible to receive 3 monthly rounds of dihydroartemisinin-piperaquine (DP). Two neighboring villages served as controls. Malaria cases were defined as individuals with a positive rapid diagnostic test result as recorded in health center registers. We performed a difference-in-differences analysis to estimate changes in the incidence and test positivity of malaria between intervention and control villages. RESULTS: A total of 554 children received at least 1 round of chemoprevention, with 75% participating in at least 2 rounds. Compared with control villages, we estimated a 53.4% reduction (adjusted rate ratio [aRR], 0.47; 95% confidence interval [CI]: .34-.62; P < .01) in malaria incidence and a 30% decrease in the test positivity rate (aRR, 0.70; 95% CI: .50-.97; P = .03) in the intervention village in the 6 months post-intervention. The impact was greatest among children who received the intervention, but decreased incidence was also observed in older children and adults (aRR, 0.57; 95% CI: .38-.84; P < .01). CONCLUSIONS: Three rounds of chemoprevention with DP delivered under pragmatic conditions reduced the incidence of malaria after severe flooding in western Uganda. These findings provide a proof-of-concept for the use of malaria chemoprevention to reduce excess disease burden associated with severe flooding.

The Nonclinical Disposition and Pharmacokinetic/Pharmacodynamic Properties of N-Acetylgalactosamine-Conjugated Small Interfering RNA Are Highly Predictable and Build Confidence in Translation to Human.

Conjugation of oligonucleotide therapeutics, including small interfering RNAs (siRNAs) or antisense oligonucleotides, to N-acetylgalactosamine (GalNAc) ligands has become the primary strategy for hepatocyte-targeted delivery, and with the recent approvals of GIVLAARI (givosiran) for the treatment of acute hepatic porphyria, OXLUMO (lumasiran) for the treatment of primary hyperoxaluria, and Leqvio (inclisiran) for the treatment of hypercholesterolemia, the technology has been well validated clinically. Although much knowledge has been gained over decades of development, there is a paucity of published literature on the drug metabolism and pharmacokinetic properties of GalNAc-siRNA. With this in mind, the goals of this minireview are to provide an aggregate analysis of these nonclinical absorption, distribution, metabolism, and excretion (ADME) data to build confidence on the translation of these properties to human. Upon subcutaneous administration, GalNAc-conjugated siRNAs are quickly distributed to the liver, resulting in plasma pharmacokinetic (PK) properties that reflect rapid elimination through asialoglycoprotein receptor-mediated uptake from circulation into hepatocytes. These studies confirm that liver PK, including half-life and, most importantly, siRNA levels in RNA-induced silencing complex in hepatocytes, are better predictors of pharmacodynamics (PD) than plasma PK. Several in vitro and in vivo nonclinical studies were conducted to characterize the ADME properties of GalNAc-conjugated siRNAs. These studies demonstrate that the PK/PD and ADME properties of GalNAc-conjugated siRNAs are highly conserved across species, are largely predictable, and can be accurately scaled to human, allowing us to identify efficacious and safe clinical dosing regimens in the absence of human liver PK profiles. SIGNIFICANCE STATEMENT: Several nonclinical ADME studies have been conducted in order to provide a comprehensive overview of the disposition and elimination of GalNAc-conjugated siRNAs and the pharmacokinetic/pharmacodynamic translation between species. These studies demonstrate that the ADME properties of GalNAc-conjugated siRNAs are well correlated and predictable across species, building confidence in the ability to extrapolate to human.

Investigating the pharmacodynamic durability of GalNAc-siRNA conjugates.

One hallmark of trivalent N-acetylgalactosamine (GalNAc)-conjugated siRNAs is the remarkable durability of silencing that can persist for months in preclinical species and humans. Here, we investigated the underlying biology supporting this extended duration of pharmacological activity. We found that siRNA accumulation and stability in acidic intracellular compartments is critical for long-term activity. We show that functional siRNA can be liberated from these compartments and loaded into newly generated Argonaute 2 protein complexes weeks after dosing, enabling continuous RNAi activity over time. Identical siRNAs delivered in lipid nanoparticles or as GalNAc conjugates were dose-adjusted to achieve similar knockdown, but only GalNAc-siRNAs supported an extended duration of activity, illustrating the importance of receptor-mediated siRNA trafficking in the process. Taken together, we provide several lines of evidence that acidic intracellular compartments serve as a long-term depot for GalNAc-siRNA conjugates and are the major contributor to the extended duration of activity observed in vivo.

The Burden of Malaria in the Democratic Republic of the Congo.

Despite evidence that older children and adolescents bear the highest burden of malaria, large malaria surveys focus on younger children. We used polymerase chain reaction data from the 2013-2014 Demographic and Health Survey in the Democratic Republic of Congo (including children aged <5 years and adults aged ≥15 years) and a longitudinal study in Kinshasa Province (participants aged 6 months to 98 years) to estimate malaria prevalence across age strata. We fit linear models and estimated prevalences for each age category; adolescents aged 10-14 years had the highest prevalence. We estimate approximately 26 million polymerase chain reaction-detectable infections nationally. Adolescents and older children should be included in surveillance studies.

Malaria prevalence and long-lasting insecticidal net use in rural western Uganda: results of a cross-sectional survey conducted in an area of highly variable malaria transmission intensity.

BACKGROUND: Long-lasting insecticidal nets (LLINs) remain a cornerstone of malaria control, but strategies to sustain universal coverage and high rates of use are not well-defined. A more complete understanding of context-specific factors, including transmission intensity and access to health facilities, may inform sub-district distribution approaches and tailored messaging campaigns. METHODS: A cross-sectional survey of 2190 households was conducted in a single sub-county of western Uganda that experiences highly variable malaria transmission intensity. The survey was carried out approximately 3 years after the most recent mass distribution campaign. At each household, study staff documented reported LLIN use and source among children 2 to 10 years of age and performed a malaria rapid diagnostic test. Elevation and distance to the nearest health facility was estimated for each household. Associations between parasite prevalence and LLIN use were estimated from log binomial regression models with elevation and distance to clinic being the primary variables of interest. RESULTS: Overall, 6.8% (148 of 2170) of children age 2-10 years of age had a positive RDT result, yielding a weighted estimate of 5.8% (95% confidence interval [CI] 5.4-6.2%). There was substantial variability in the positivity rates among villages, with the highest elevation villages having lower prevalence than lowest-elevation villages (p < .001). Only 64.7% (95% CI 64.0-65.5%) of children were reported to have slept under a LLIN the previous night. Compared to those living < 1 km from a health centre, households at ≥ 2 km were less likely to report the child sleeping under a LLIN (RR 0.86, 95% CI 0.83-0.89, p < .001). Households located farther from a health centre received a higher proportion of LLINs from government distributions compared to households living closer to health centres. CONCLUSIONS: LLIN use and sourcing was correlated with household elevation and estimated distance to the nearest health facility. The findings suggest that current facility-based distribution strategies are limited in their reach. More frequent mass distribution campaigns and complementary approaches are likely required to maintain universal LLIN coverage and high rates of use among children in rural Uganda.

Nab-paclitaxel: An effective third-line chemotherapy in patients with advanced, unresectable gallbladder cancer.

BACKGROUND & OBJECTIVES: Gallbladder (GBC) is an aggressive form of cancer and most patients present with advanced unresectable disease due to lack of early signs and symptoms. This retrospective study was conducted to present the treatment outcomes with three lines of chemotherapies in a subset of patients with advanced, unresectable GBC with the primary objective to determine the response rates with nab-paclitaxel as the third-line chemotherapy after failure of the first-line gemcitabine and platinum and the second-line FOLFOX-4 (oxaliplatin, leucovorin and 5-FU) therapy. Another objective was to evaluate the toxicity, progression-free survival (PFS) and overall survival (OS). METHODS: Treatment-naive patients with histologically proven inoperable GBC treated with gemcitabine/platinum, FOLFOX-4 and nab-paclitaxel as the first-, second- and third-line chemotherapy were included in this study. The dose of gemcitabine and cisplatin or carboplatin was 1 g/m[2] on days 1 and 8 and 75 mg/m[2] (or target AUC of 5) on day 1, in a 21-day cycle. FOLFOX-4 was administered every two weeks and nab-paclitaxel was administered as 125 mg/m[2] on days 1, 8 and 15 in a 28-day cycle. RESULTS: There were eight men and 13 women with a median age of 57 yr who received nab-paclitaxel therapy. The overall response rate of the first-, second- and third-line chemotherapy was 61.9, 57.1 and 52.4 per cent, respectively. The median PFS for the gemcitabine/platinum, FOLFOX-4 and nab-paclitaxel therapy was 5.5, 5.4 and 2.9 months, respectively. The median OS with three lines of therapies was 14.0 months. Common Terminology Criteria (CTC) grade 3 or 4 haematological toxicities were observed in 28.6, 38.1 and 23.8 per cent of patients on gemcitabine/platinum, FOLFOX-4 and nab-paclitaxel therapy, respectively. INTERPRETATION & CONCLUSIONS: Our study suggests the clinical benefit of nab-paclitaxel chemotherapy in prolonging OS in a selected subgroup of advanced, unresectable GBC patients after failure of the first-line gemcitabine and platinum and the second-line FOLFOX-4 therapy.

Correction to: Individual and household characteristics of persons with Plasmodium falciparum malaria in sites with varying endemicities in Kinshasa Province, Democratic Republic of the Congo.

Unfortunately after publication of the original article [1], it came to the author's attention that there is an error in the caption of Fig. 2.

Individual and household characteristics of persons with Plasmodium falciparum malaria in sites with varying endemicities in Kinshasa Province, Democratic Republic of the Congo.

BACKGROUND: The Democratic Republic of the Congo (DRC) bears a large share of global malaria burden despite efforts to control and eliminate the disease. More detailed understanding of individual and household level characteristics associated with malaria are needed, as is an understanding of how these characteristics vary spatiotemporally and across different community-level malaria endemicities. An ongoing study in Kinshasa Province is designed to address gaps in prior malaria surveillance in the DRC by monitoring malaria across seasons, age groups and in high and low malaria sites. Across seven sites, 242 households and 1591 individuals are participating in the study. Results of the enrollment questionnaire, rapid diagnostic tests and PCR testing of dried blood spots are presented. RESULTS: Overall malaria prevalence in the study cohort is high, 27% by rapid diagnostic test and 31% by polymerase chain reaction, and malaria prevalence is highly varied across very small geographic distances. Malaria prevalence is highest in children aged 6-15. While the majority of households own bed nets, bed net usage is less than 50%. CONCLUSIONS: The study cohort will provide an understanding of how malaria persists in populations that have varying environmental exposures, varying community-level malaria, and varying access to malaria control efforts.

FOLFOX-4 as second-line therapy after failure of gemcitabine and platinum combination in advanced gall bladder cancer patients.

OBJECTIVE: There is no standard second-line chemotherapy after progression on first-line therapy including gemcitabine and platinum combination in advanced gall bladder cancer patients. So this study was undertaken to assess the efficacy and safety of FOLFOX-4 regimen in this setting. METHODS: In this observational study, patients with performance status ≤2, who progressed on first-line therapy, were enrolled from May 2010 to June 2014. FOLFOX-4 based treatment was administered until progression, unacceptable toxicity or up to 12 cycles. RESULTS: A total of 66 patients were enrolled in this study. The median age of patients was 52.5 years (32-66 years),of which 24 (36.36%) were males and 42 (63.63%) were females. The median number of cycles could be given were 9.5 (2-12). Only 43.93% patients in this study completed full 12 cycles of chemotherapy. Sixteen patients (24.24%) in this study required the dose reduction at least in one cycle of chemotherapy due to toxicities. Disease control rate was seen in 39 (59.09%) patients, with complete response in none, partial response in 16 (24.24%), stable disease in 23 (34.84%) and progressive disease in 27 (40.90%) patients. The median progression free survival was 3.9 months; median overall survival was 7.6 months. The main Grade 3/4 side effects seen were hematological in 31.81% (n = 21) and gastrointestinal in 25.75% (n = 17) patients. Majority of patients (46%) had Grade 1/2 peripheral neuropathy. CONCLUSIONS: FOLFOX-4 is an effective and well-tolerated regimen as a second-line treatment in advanced gall bladder cancer patients. Further studies are required, especially in the Indian subcontinent.

Synchronous Triple Malignancy of Esophagus, Pancreas, and Pyriform Sinus: A Prima Facie Report.

The occurrence of triple synchronous primary malignant neoplasms is very rare. With improved cancer detection rates, widespread screening techniques and their availability, and improved general awareness, there has been a rise in the detection rate of patients with multiple primaries. Most of these cases consist of dual synchronous malignancies. However, triple synchronous malignancies have been reported and are extremely rare in literature. In such cases, the etiology is unknown most of the time, and management of such a situation remains challenging. We report such a case in a 71-year-old male with no genetic predisposition or family history of malignancy, presenting with three primary malignancies of the buccal mucosa, esophagus, and pancreas. Investigations revealed three histologically separate tumors in the buccal mucosa, esophagus, and pancreas. The patient was treated initially with a first-line combination of chemotherapy and later with a 2nd-line palliative chemotherapy. The prognosis of such patients is poor. Our patient is still on 2nd-line palliative chemotherapy without any major complications.

Self-powered photodetectors: a device engineering perspective.

Nanoscale self-powered photodetectors that can work without any external source of energy are required for future applications. There is potential demand for these devices in areas like wireless surveillance, weather forecasting, remote monitoring, and places where the availability of power is scarce. This study provides an overview of state of the art research trends and improvements in self-powered photodetectors. A device engineering perspective for improvement in the figures of merit has been presented along with a description of additional effects like pyro-phototronic, piezo-phototronic, and surface plasmonics.

Provisional Entrants, Exemptions, and Kindergarteners Up-to-Date on Vaccination Before and After a Regulatory Change in Pennsylvania, 2015-2019.

OBJECTIVES: Before the 2017-2018 school year, Pennsylvania shortened the grace period for provisional entrants-kindergarteners who are not up-to-date on vaccination and do not have medical or nonmedical exemption-from 8 months to 5 days. We analyzed the impact of this change on school-entry vaccination status. METHODS: Using data from the Pennsylvania Department of Health for school years 2015-2016 through 2018-2019, we examined state-level trends in Pennsylvania kindergarteners' vaccination status, including the percentage who were up-to-date on each required vaccine, provisionally enrolled, medically exempted from vaccination, and nonmedically exempted from vaccination. Using the Spearman correlation coefficient, we assessed associations at the school level among changes in kindergarteners' vaccination status after the grace period was shortened. RESULTS: From 2016-2017 to 2017-2018, the provisional entrance rate of kindergarteners in Pennsylvania decreased substantially after the change in the grace period (from 8.1% to 2.2%), the medical exemption rate remained stable, and the nonmedical exemption rate increased slightly (from 1.8% to 2.5%). The percentage of kindergarteners up-to-date on required vaccines increased or remained stable across the study period except for polio, which decreased from 97.9% in 2015-2016 to 96.2% in 2018-2019. The change in provisional entrance rate was negatively associated with change in kindergarteners up-to-date on required vaccines (ρ range, -0.30 to -0.70) but not with change in medical or nonmedical exemptions (ρ range, -0.01 to -0.08). CONCLUSIONS: Efforts to reduce provisional entrants may increase the percentage of kindergarteners up-to-date on vaccinations at school entry without a corresponding increase in exemptions.

Spatial patterns of influenza A virus spread across compartments in commercial swine farms in the United States.

Multiple genetic variants of H1 and H3 influenza A viruses (IAVs) circulate concurrently in US swine farms. Understanding the spatial transmission patterns of IAVs among these farms is crucial for developing effective control strategies and mitigating the emergence of novel IAVs. In this study, we analysed 1909 IAV genomic sequences from 785 US swine farms, representing 33 farming systems across 12 states, primarily in the Midwest from 2004 to 2023. Bayesian phylogeographic analyses were performed to identify the dispersal patterns of both H1 and H3 virus genetic lineages and to elucidate their spatial migration patterns within and between different systems. Our results showed that both intra-system and inter-system migrations occurred between the swine farms, with intra-system migrations being more frequent. However, migration rates for H1 and H3 IAVs were similar between intra-system and inter-system migration events. Spatial migration patterns aligned with expected pig movement across different compartments of swine farming systems. Sow-Farms were identified as key sources of viruses, with bi-directional migration observed between these farms and other parts of the system, including Wean-to-Finish and Gilt-Development-Units. High intra-system migration was detected across farms in the same region, while spread to geographically distant intra- and inter-system farms was less frequent. These findings suggest that prioritizing resources towards systems frequently confronting influenza problems and targeting pivotal source farms, such as sow farms, could be an effective strategy for controlling influenza in US commercial swine operations.

Strong isolation by distance and evidence of population microstructure reflect ongoing Plasmodium falciparum transmission in Zanzibar.

The Zanzibar archipelago of Tanzania has become a low-transmission area for Plasmodium falciparum. Despite being considered an area of pre-elimination for years, achieving elimination has been difficult, likely due to a combination of imported infections from mainland Tanzania, and continued local transmission. To shed light on these sources of transmission, we applied highly multiplexed genotyping utilizing molecular inversion probes to characterize the genetic relatedness of 282 P. falciparum isolates collected across Zanzibar and in Bagamoyo District on the coastal mainland from 2016-2018. Overall, parasite populations on the coastal mainland and Zanzibar archipelago remain highly related. However, parasite isolates from Zanzibar exhibit population microstructure due to rapid decay of parasite relatedness over very short distances. This, along with highly related pairs within shehias, suggests ongoing low level local transmission. We also identified highly related parasites across shehias that reflect human mobility on the main island of Unguja and identified a cluster of highly related parasites, suggestive of an outbreak, in the Micheweni district on Pemba island. Parasites in asymptomatic infections demonstrated higher complexity of infection than those in symptomatic infections, but have similar core genomes. Our data support importation as a main source of genetic diversity and contribution to the parasite population on Zanzibar, but they also show local outbreak clusters where targeted interventions are essential to block local transmission. These results highlight the need for preventive measures against imported malaria and enhanced control measures in areas that remain receptive for malaria reemergence due to susceptible hosts and competent vectors.

Strong isolation by distance and evidence of population microstructure reflect ongoing Plasmodium falciparum transmission in Zanzibar.

Background: The Zanzibar archipelago of Tanzania has become a low-transmission area for Plasmodium falciparum. Despite being considered an area of pre-elimination for years, achieving elimination has been difficult, likely due to a combination of imported infections from mainland Tanzania and continued local transmission. Methods: To shed light on these sources of transmission, we applied highly multiplexed genotyping utilizing molecular inversion probes to characterize the genetic relatedness of 282 P. falciparum isolates collected across Zanzibar and in Bagamoyo district on the coastal mainland from 2016 to 2018. Results: Overall, parasite populations on the coastal mainland and Zanzibar archipelago remain highly related. However, parasite isolates from Zanzibar exhibit population microstructure due to the rapid decay of parasite relatedness over very short distances. This, along with highly related pairs within shehias, suggests ongoing low-level local transmission. We also identified highly related parasites across shehias that reflect human mobility on the main island of Unguja and identified a cluster of highly related parasites, suggestive of an outbreak, in the Micheweni district on Pemba island. Parasites in asymptomatic infections demonstrated higher complexity of infection than those in symptomatic infections, but have similar core genomes. Conclusions: Our data support importation as a main source of genetic diversity and contribution to the parasite population in Zanzibar, but they also show local outbreak clusters where targeted interventions are essential to block local transmission. These results highlight the need for preventive measures against imported malaria and enhanced control measures in areas that remain receptive to malaria reemergence due to susceptible hosts and competent vectors. Funding: This research was funded by the National Institutes of Health, grants R01AI121558, R01AI137395, R01AI155730, F30AI143172, and K24AI134990. Funding was also contributed from the Swedish Research Council, Erling-Persson Family Foundation, and the Yang Fund. RV acknowledges funding from the MRC Centre for Global Infectious Disease Analysis (reference MR/R015600/1), jointly funded by the UK Medical Research Council (MRC) and the UK Foreign, Commonwealth & Development Office (FCDO), under the MRC/FCDO Concordat agreement and is also part of the EDCTP2 program supported by the European Union. RV also acknowledges funding by Community Jameel.