Stone et al. Malar J (2015) 14:451 DOI 10.1186/s12936-015-0954-2RESEARCHA comparison of Plasmodium falciparum circumsporozoite protein-based slot blot and ELISA immuno-assays for oocyst detection in mosquito homogenatesWill Stone 1 , Bryan Grabias 2 , Kjerstin Lanke 1 , Hong Zheng 2 , Emily Locke 3 , Diadier Diallo 3 , Ashley Birkett 3 , Merribeth Morin 3 , Teun Bousema 1,4* and Sanjai Kumar 2Abstract Background: The infectivity of Plasmodium gametocytes is typically determined by microscopically examining the midguts of mosquitoes that have taken a blood meal containing potentially infectious parasites. Such assessments are required for the development and evaluation of transmission-reducing interventions (TRI), but are limited by subjectivity, technical complexity and throughput. The detection of circumsporozoite protein (CSP) by enzyme-linked immunosorbent assay (ELISA) and enhanced chemiluminescent slot-blot (ECL-SB) may be used as objective, scalable alternatives to microscopy for the determination of infection prevalence.Methods: To compare the performance of the CSP ELISA and ECL-SB for the detection of mosquito infection, four groups of Anopheles stephensi mosquitoes were infected with cultured Plasmodium falciparum gametocytes. At day-8 post-infection (PI), parasite status was determined by microscopy for a sample of mosquitoes from each group. At days 8 and 10 PI, the parasite status of separate mosquito samples was analysed by both CSP ELISA and ECL-SB.Results: When mosquito samples were analysed 8 days PI, the ECL-SB determined similar infection prevalence to microscopy; CSP ELISA lacked the sensitivity to detect CSP in all infected mosquitoes at this early time point. When mosquitoes were analysed 48 h later (10 days PI) both assays performed as well as microscopy for infection detection.Conclusions: Whilst microscopical examination of mosquito guts is of great value when quantif i cation of para-site burden is required, ECL-SB and CSP ELISA are suitable alternatives at day 10 PI when infection prevalence is the desired endpoint, although CSP ELISA is not suitable at day 8 PI. These results are important to groups considering large-scale implementation of TRI.Keywords: Plasmodium falciparum, Anopheles, Sporozoite, Oocyst, Circumsporozoite protein, ELISA, Slot-blot, Immuno-assay, Mosquito infection© 2015 Stone et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.BackgroundTransmission-reducing interventions (TRIs) that spe-cif i cally aim to interrupt the transmission of malaria from man to mosquito form important components of malaria control and elimination strategies [1, 2]. Th e development, targeting and evaluation of TRIs requires robust assessments of the infectivity of human malaria infections to mosquitoes [3, 4]. Mosquito infection sta-tus is typically determined by microscopy following the observation of Plasmodium oocysts in the midgut or sporozoites in the salivary glands [5, 6]. Oocysts develop on the basal lamina of the mosquito midgut approxi-mately 2 days after the ingestion of a blood meal contain-ing infectious gametocytes, and can be visually detected by microscopy approximately 6 days post infection (PI) Open Access*Correspondence: teun.bousema@radboudumc.nl 1 Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Nijmegen, The NetherlandsFull list of author information is available at the end of the article
