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The prevalence and density of asymptomatic Plasmodium falciparum infections among children and adults in three communities of western Kenya.

Publication ,  Journal Article
Salgado, C; Ayodo, G; Macklin, MD; Gould, MP; Nallandhighal, S; Odhiambo, EO; Obala, A; O'Meara, WP; John, CC; Tran, TM
Published in: Malar J
September 17, 2021

BACKGROUND: Further reductions in malaria incidence as more countries approach malaria elimination require the identification and treatment of asymptomatic individuals who carry mosquito-infective Plasmodium gametocytes that are responsible for furthering malaria transmission. Assessing the relationship between total parasitaemia and gametocytaemia in field surveys can provide insight as to whether detection of low-density, asymptomatic Plasmodium falciparum infections with sensitive molecular methods can adequately detect the majority of infected individuals who are potentially capable of onward transmission. METHODS: In a cross-sectional survey of 1354 healthy children and adults in three communities in western Kenya across a gradient of malaria transmission (Ajigo, Webuye, and Kapsisywa-Kipsamoite), asymptomatic P. falciparum infections were screened by rapid diagnostic tests, blood smear, and quantitative PCR of dried blood spots targeting the varATS gene in genomic DNA. A multiplex quantitative reverse-transcriptase PCR assay targeting female and male gametocyte genes (pfs25, pfs230p), a gene with a transcriptional pattern restricted to asexual blood stages (piesp2), and human GAPDH was also developed to determine total parasite and gametocyte densities among parasitaemic individuals. RESULTS: The prevalence of varATS-detectable asymptomatic infections was greatest in Ajigo (42%), followed by Webuye (10%). Only two infections were detected in Kapsisywa. No infections were detected in Kipsamoite. Across all communities, children aged 11-15 years account for the greatest proportion total and sub-microscopic asymptomatic infections. In younger age groups, the majority of infections were detectable by microscopy, while 68% of asymptomatically infected adults (> 21 years old) had sub-microscopic parasitaemia. Piesp2-derived parasite densities correlated poorly with microscopy-determined parasite densities in patent infections relative to varATS-based detection. In general, both male and female gametocytaemia increased with increasing varATS-derived total parasitaemia. A substantial proportion (41.7%) of individuals with potential for onward transmission had qPCR-estimated parasite densities below the limit of microscopic detection, but above the detectable limit of varATS qPCR. CONCLUSIONS: This assessment of parasitaemia and gametocytaemia in three communities with different transmission intensities revealed evidence of a substantial sub-patent infectious reservoir among asymptomatic carriers of P. falciparum. Experimental studies are needed to definitively determine whether the low-density infections in communities such as Ajigo and Webuye contribute significantly to malaria transmission.

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Published In

Malar J

DOI

EISSN

1475-2875

Publication Date

September 17, 2021

Volume

20

Issue

1

Start / End Page

371

Location

England

Related Subject Headings

  • Young Adult
  • Tropical Medicine
  • Rural Population
  • Prevalence
  • Middle Aged
  • Male
  • Malaria, Falciparum
  • Kenya
  • Infant
  • Humans
 

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Salgado, C., Ayodo, G., Macklin, M. D., Gould, M. P., Nallandhighal, S., Odhiambo, E. O., … Tran, T. M. (2021). The prevalence and density of asymptomatic Plasmodium falciparum infections among children and adults in three communities of western Kenya. Malar J, 20(1), 371. https://doi.org/10.1186/s12936-021-03905-w
Salgado, Christina, George Ayodo, Michael D. Macklin, Meetha P. Gould, Srinivas Nallandhighal, Eliud O. Odhiambo, Andrew Obala, Wendy Prudhomme O’Meara, Chandy C. John, and Tuan M. Tran. “The prevalence and density of asymptomatic Plasmodium falciparum infections among children and adults in three communities of western Kenya.Malar J 20, no. 1 (September 17, 2021): 371. https://doi.org/10.1186/s12936-021-03905-w.
Salgado C, Ayodo G, Macklin MD, Gould MP, Nallandhighal S, Odhiambo EO, et al. The prevalence and density of asymptomatic Plasmodium falciparum infections among children and adults in three communities of western Kenya. Malar J. 2021 Sep 17;20(1):371.
Salgado, Christina, et al. “The prevalence and density of asymptomatic Plasmodium falciparum infections among children and adults in three communities of western Kenya.Malar J, vol. 20, no. 1, Sept. 2021, p. 371. Pubmed, doi:10.1186/s12936-021-03905-w.
Salgado C, Ayodo G, Macklin MD, Gould MP, Nallandhighal S, Odhiambo EO, Obala A, O’Meara WP, John CC, Tran TM. The prevalence and density of asymptomatic Plasmodium falciparum infections among children and adults in three communities of western Kenya. Malar J. 2021 Sep 17;20(1):371.
Journal cover image

Published In

Malar J

DOI

EISSN

1475-2875

Publication Date

September 17, 2021

Volume

20

Issue

1

Start / End Page

371

Location

England

Related Subject Headings

  • Young Adult
  • Tropical Medicine
  • Rural Population
  • Prevalence
  • Middle Aged
  • Male
  • Malaria, Falciparum
  • Kenya
  • Infant
  • Humans