Erschienen:
Springer Science and Business Media LLC, 2021
Erschienen in:Malaria Journal
Sprache:
Englisch
DOI:
10.1186/s12936-021-03905-w
ISSN:
1475-2875
Entstehung:
Anmerkungen:
Beschreibung:
<jats:title>Abstract</jats:title><jats:sec>
<jats:title>Background</jats:title>
<jats:p>Further reductions in malaria incidence as more countries approach malaria elimination require the identification and treatment of asymptomatic individuals who carry mosquito-infective <jats:italic>Plasmodium</jats:italic> 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 <jats:italic>Plasmodium falciparum</jats:italic> infections with sensitive molecular methods can adequately detect the majority of infected individuals who are potentially capable of onward transmission.</jats:p>
</jats:sec><jats:sec>
<jats:title>Methods</jats:title>
<jats:p>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 <jats:italic>P. falciparum</jats:italic> infections were screened by rapid diagnostic tests, blood smear, and quantitative PCR of dried blood spots targeting the <jats:italic>varATS</jats:italic> gene in genomic DNA. A multiplex quantitative reverse-transcriptase PCR assay targeting female and male gametocyte genes (<jats:italic>pfs25</jats:italic>, <jats:italic>pfs230p</jats:italic>), a gene with a transcriptional pattern restricted to asexual blood stages (<jats:italic>piesp2</jats:italic>), and human <jats:italic>GAPDH</jats:italic> was also developed to determine total parasite and gametocyte densities among parasitaemic individuals.</jats:p>
</jats:sec><jats:sec>
<jats:title>Results</jats:title>
<jats:p>The prevalence of <jats:italic>varATS</jats:italic>-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. <jats:italic>Piesp2</jats:italic>-derived parasite densities correlated poorly with microscopy-determined parasite densities in patent infections relative to <jats:italic>varATS</jats:italic>-based detection. In general, both male and female gametocytaemia increased with increasing <jats:italic>varATS</jats:italic>-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 <jats:italic>varATS</jats:italic> qPCR.</jats:p>
</jats:sec><jats:sec>
<jats:title>Conclusions</jats:title>
<jats:p>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 <jats:italic>P. falciparum</jats:italic>. Experimental studies are needed to definitively determine whether the low-density infections in communities such as Ajigo and Webuye contribute significantly to malaria transmission.</jats:p>
</jats:sec>