Frequent and genetically diverse Plasmodium vivax relapses contribute to malaria transmission in Cambodia

Frequent and genetically diverse Plasmodium vivax relapses contribute to malaria transmission in Cambodia | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Frequent and genetically diverse Plasmodium vivax relapses contribute to malaria transmission in Cambodia Jean Popovici, Dynang Seng, Katie Ko, Agnes Orban, Sokleap Heng, and 11 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9199901/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract A unique feature of Plasmodium vivax is the presence of dormant hypnozoites that cause relapses weeks after the initial infection. While relapses may account for the majority of vivax malaria cases, the determinants of relapse periodicity, the genetic relationships between parasites, and the transmission potential of relapsing parasites in endemic populations remain poorly understood. We characterized P. vivax relapses in a cohort of 59 Cambodian patients treated with artesunate and relocated to a malaria-free area to prevent reinfection. Participants were followed every two days for 90 days using qPCR and microscopy. Genomes of blood stage parasites were sequenced to determine clonality and genetic relatedness between initial and relapsing infections. Membrane-feeding assays using Anopheles dirus mosquitoes were performed to evaluate the transmission potential of relapse infections. Relapses occurred frequently, with 81% of the patients experiencing at least one relapse within 90 days, with up to four consecutive relapses per individual and a median time to first relapse of 20 days. Genome sequencing revealed that relapsing parasites in monoclonal infections could be genetically identical, siblings of, or unrelated to the parasites present at enrollment. Patients with polyclonal infections at enrollment experienced significantly more relapses than those with monoclonal infections, suggesting that infection complexity may reflect the heterogeneity of the hypnozoite reservoir. Parasite growth rates during relapses varied widely among individuals but were associated with the degree of relatedness to those present in the initial infection. Despite low parasitemia and the absence of symptoms in most cases, relapse infections were frequently infectious to mosquitoes in membrane-feeding assays. Our findings show that P. vivax relapses occur commonly and frequently, and often involve genetically distinct parasites, reflecting complex hypnozoite reservoirs. Importantly, even low-density relapse infections can transmit efficiently to mosquitoes, highlighting the critical role of hypnozoites in sustaining malaria transmission and the importance of radical cure strategies for vivax malaria elimination. Biological sciences/Microbiology/Parasitology/Parasite biology Biological sciences/Microbiology/Parasitology/Parasite genomics Plasmodium vivax malaria relapses hypnozoites transmission complexity of infection Full Text Additional Declarations There is NO Competing Interest. Supplementary Files Supplementalinfo06March2026acfinal.docx Supp. Info Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9199901","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":611378989,"identity":"75c7670b-6b24-45c0-8137-1c0052b5be7b","order_by":0,"name":"Jean 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While relapses may account for the majority of vivax malaria cases, the determinants of relapse periodicity, the genetic relationships between parasites, and the transmission potential of relapsing parasites in endemic populations remain poorly understood. \r\nWe characterized P. vivax relapses in a cohort of 59 Cambodian patients treated with artesunate and relocated to a malaria-free area to prevent reinfection. Participants were followed every two days for 90 days using qPCR and microscopy. Genomes of blood stage parasites were sequenced to determine clonality and genetic relatedness between initial and relapsing infections. Membrane-feeding assays using Anopheles dirus mosquitoes were performed to evaluate the transmission potential of relapse infections.\r\nRelapses occurred frequently, with 81% of the patients experiencing at least one relapse within 90 days, with up to four consecutive relapses per individual and a median time to first relapse of 20 days. 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