Determining the prevalence and density of asymptomatic Plasmodium falciparum infections in low and high transmission settings in Western Kenya

Authors

  • Christina Salgado Indiana University School of Medicine
  • Erik Gaskin Indiana University School of Medicine
  • Michael Macklin Indiana University School of Medicine
  • Eliud Onyango Indiana University School of Medicine
  • Rachel Surridge Indiana University School of Medicine
  • Srinivas Nallandhighal Michigan Medicine
  • Jyoti Bhardwaj Indiana University School of Medicine
  • Dibyadyuti Datta Indiana University School of Medicine
  • Lindsey Turnbull Indiana University School of Medicine
  • Wendy O'Meara Duke University
  • George Ayodo Kenya Medical Research Institute
  • Chandy John Indiana University School of Medicine
  • Tuan Tran Indiana University School of Medicine

DOI:

https://doi.org/10.18060/24748

Abstract

Background/Objective: Malaria remains a global health burden as 2018 saw 228 million cases worldwide. Pre-elimination efforts aim to decrease disease transmission, which depends on development of asexual parasites to sexual gametocytes within the human host. To better determine the relationship between asexual parasites and gametocytes, we aim to quantify both stages within the same blood sample by developing a multiplex RT-qPCR assay. We hypothesize that gametocytemia decreases linearly with asexual parasitemia at higher parasitemias but increases at lower parasitemia to improve transmission probability.  

 

Methods: We conducted a cross-sectional survey of healthy participants aged 0 to 92 years at four sites in Western Kenya (Ajigo, Webuye, Kipsamoite, Kapsisywa) with varying levels of transmission to determine prevalence of asymptomatic P. falciparum blood-stage infections. Parasite density was quantified by light microscopy and by quantitative PCR of genomic DNA isolated from dried blood spots using varATS primers. For varATS-positive samples, we isolated RNA from whole-blood and performed stage-specific quantification by multiplex Taqman RT-qPCR  targeting PfPIESP2 (asexual), Pfs25 (female), and Pfs230p (male).  

 

Results: Among all participants, 127 of 1355 (9.37%) were positive for asymptomatic P. falciparum infection by varATS-qPCR. Using varATS positivity as the standard, multiplex RT-qPCR  targeting PfPIESP2 yielded a sensitivity of 78%.  Across sites, overall parasite prevalence and gametocyte prevalence were highest in Ajigo (42.1%; 36%) followed by Webuye (10.5%; 9%) and Kipsamoite/Kapsisywa (0.873%; 0.1%). Pfs25-quantified gametocytemia decreased with decreasing varATS-quantified asexual parasitemia; however, the data poorly fit a linear model (R2 = 0.088).   

 

Conclusions: PfPIESP2 detected 78% of varATS-positive samples, suggesting it may be poorly sensitive at detecting low-density blood-stage infections. Assay design may improve with a more sensitive gene target and further optimization. Based on quantification results, the relationship between gametocytemia and asexual parasitemia appears direct but non-linear. Further work is necessary to better model the relationship between stage-specific parasitemia levels. 

Author Biographies

Erik Gaskin, Indiana University School of Medicine

Department of Infectious Disease

Michael Macklin, Indiana University School of Medicine

 Department of Infectious Disease

Eliud Onyango, Indiana University School of Medicine

Department of Infectious Disease

Rachel Surridge, Indiana University School of Medicine

Department of Infectious Disease

Srinivas Nallandhighal, Michigan Medicine

Department of Urology

Jyoti Bhardwaj, Indiana University School of Medicine

Department of Infectious Disease

Dibyadyuti Datta, Indiana University School of Medicine

Department of Infectious Disease

Lindsey Turnbull, Indiana University School of Medicine

Department of Infectious Disease

Wendy O'Meara, Duke University

Duke University, Duke Global Health Institute

Duke University School of Medicine, Division of Infectious Disease

George Ayodo, Kenya Medical Research Institute

Kenya Medical Research Institute, Center for Global Health Research

Jaramogi Oginga Odinga University of Science and Technology

Chandy John, Indiana University School of Medicine

Department of Infectious Disease

Tuan Tran, Indiana University School of Medicine

Department of Infectious Disease

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Published

2020-12-15

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Abstracts