Publications & Reports

Molecular and immunofluorescence-based quantification of male and female gametocytes in low-density P. falciparum infections and their relevance for transmission.

Gruenberg M, Hofmann NE, Nate E, Karl S, Robinson LJ, Lanke K, Smith TA, Bousema T, Felger I
Swiss Tropical and Public Health Institute, Basel, Switzerland.

Abstract

BACKGROUND: Accurate quantification of female and male gametocytes and sex-ratios in low-density malaria infections are important for assessing the transmission potential of asymptomatic infections. Gametocytes often escape detection even by molecular methods, therefore ultra-low gametocyte densities were quantified in large blood volumes. METHODS: Female and male gametocytes were quantified in 161 PCR-positive Plasmodium falciparum (Pf) infections from a cross-sectional survey in Papua New Guinea. Ten-fold concentrated RNA from 800microL blood was analysed using female-specific pfs25 and male-specific pfmget or mssp qRT-PCR. Gametocyte sex-ratios by qRT-PCR were compared with those obtained from immunofluorescence assays (IFA). RESULTS: Gametocytes were identified in 58% (93/161) Pf-positive individuals. Mean gametocyte densities were frequently below 1 female and 1 male gametocyte/microL by qRT-PCR. The mean proportion of males was 0.39 [95%CI: 0.33; 0.44] by pfs25/pfmget. The proportion of males correlated well between IFA and qRT-PCR (Pearsons r2=0.91; p<0.001). A Poisson model fitted to our data predicted 16% Pf-positive individuals that are likely to transmit, assuming at least 1 female and 1 male gametocyte per 2.5microL average volume of a mosquito bloodmeal. CONCLUSIONS: Based on model estimates of female and male gametocytes per 2.5microL blood, Pf-positive individuals, detected exclusively by ultra-sensitive diagnostics, are negligible for human-to-mosquito transmission.

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Publication

  • Journal: The Journal of Infectious Diseases
  • Published: 01/01/2020
  • Volume: Epub ahead of print

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