Uneven Plasmodium falciparum transmission and cryptic ovale transmission from the asymptomatic reservoir in Bagamoyo, Tanzania

Jessica T Lin; Derrick K Mathias; Guozheng Yang; Mwajabu Loya; Meredith S Muller; Christopher Basham; Vincent Nyasembe; Kano Amagai; Isaack Rutha; Claudia Gaither; Mwanaidi Nyange; Hamza Said; Srijana B Chhetri; Brian Swinehart; Feng-Chang Lin; Rhoel R Dinglasan; Jonathan J Juliano; Brian Tarimo; Billy Ngasala

doi:10.1093/infdis/jiaf634

Uneven Plasmodium falciparum transmission and cryptic ovale transmission from the asymptomatic reservoir in Bagamoyo, Tanzania

J Infect Dis. 2025 Dec 13:jiaf634. doi: 10.1093/infdis/jiaf634. Online ahead of print.

Authors

Jessica T Lin^{1

2}, Derrick K Mathias³, Guozheng Yang¹, Mwajabu Loya⁴, Meredith S Muller¹, Christopher Basham¹, Vincent Nyasembe⁵, Kano Amagai¹, Isaack Rutha⁴, Claudia Gaither⁶, Mwanaidi Nyange⁴, Hamza Said⁴, Srijana B Chhetri¹, Brian Swinehart¹, Feng-Chang Lin⁵, Rhoel R Dinglasan⁶, Jonathan J Juliano^{1

6}, Brian Tarimo⁷, Billy Ngasala⁴

Affiliations

¹ Institute of Global Health and Infectious Diseases, University of North Carolina, Chapel Hill, NC, USA.
² Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC, USA.
³ Florida Medical Entomology Laboratory, Institute of Food & Agricultural Sciences, University of Florida, Vero Beach, FL, USA.
⁴ Department of Parasitology and Medical Entomology, Muhimbili University of Health and Allied Sciences, Dar es Salaam, Tanzania.
⁵ Gillings School of Global Public Health, University of North Carolina, Chapel Hill, NC, USA.
⁶ Department of Infectious Diseases & Immunology and Emerging Pathogens Institute, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA.
⁷ Vector Immunity and Transmission Biology Unit, Department of Environmental Health and Ecological Sciences, Ifakara Health Institute-Bagamoyo Office, Bagamoyo, Tanzania.

PMID: 41386967
DOI: 10.1093/infdis/jiaf634

Abstract

Background: Asymptomatic malaria carriers often harbor low parasite densities missed by rapid diagnostic tests (RDTs), yet they contribute to transmission. Direct skin feeding assays (DSFs) can sensitively measure their infectiousness to mosquitoes.

Methods: To characterize human-to-mosquito transmission from the asymptomatic reservoir in Bagamoyo, Tanzania, DSFs were performed in persons >5 years of age positive for P. falciparum by RDT or real-time PCR. Fifty colony-reared Anopheles gambiae were fed on the posterior calves. Successful mosquito infection was defined as ≥1 oocyst-positive mosquito midgut among 25 dissected eight days post-skin feeding.

Results: Among 491 participants with median parasite density of 5.1 parasites/uL who underwent DSF, 22% were infectious to mosquitoes. RDT-positive participants infected roughly twice as many mosquitoes compared to RDT-negative/PCR-positive persons. However, up to 21% of infectious carriers were PCR-negative at the time of skin feeding, after screening PCR-positive a few days earlier. Overall, 9.1% (342/3,741) of mosquitoes fed on infectious carriers were parasite-positive at dissection. Half of infectious individuals infected a single mosquito, while the top 16 transmitters (3% of those undergoing DSF) cumulatively infected 57% of infected mosquitoes. RDT-positive school-age children (6-15yo), 27% of the DSF cohort, contributed to 58% of infected mosquitoes. Unexpectedly, mosquito midguts from 39 DSFs (44% of oocyst-positive feeds analyzed) tested positive for Plasmodium ovale.

Conclusions: Parasites circulating at the limit of PCR detection commonly infect mosquitoes. However, a small proportion of highly infectious carriers contribute disproportionately to transmission, offering potential for targeted interventions. Plasmodium ovale was frequently co-transmitted with P. falciparum to mosquitoes.

Keywords: Anopheles gambiae; Plasmodium falciparum; Plasmodium ovale; Tanzania; asymptomatic malaria; infectious reservoir; infectiousness; malaria transmission; mosquito feeding assay; skin feeding.

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