Abstract
BackgroundAnopheles species identification is essential for an effective malaria vector control programme. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) has been developed to identify adult Anopheles species, using the legs or the cephalothorax. The protein repertoire from arthropods can vary according to compartment, but there is no general consensus regarding the anatomic part to be used.MethodsTo determine the body part of the Anopheles mosquitoes best suited for the identification of field specimens, a mass spectral library was generated with head, thorax with wings and legs of Anopheles gambiae, Anopheles arabiensis and Anopheles funestus obtained from reference centres. The MSL was evaluated using two independent panels of 52 and 40 An. gambiae field-collected in Mali and Guinea, respectively. Geographic variability was also tested using the panel from Mali and several databases containing added specimens from Mali and Senegal.ResultsUsing the head and a database without specimens from the same field collection, the proportion of interpretable and correct identifications was significantly higher than using the other body parts at a threshold value of 1.7 (p < 0.0001). The thorax of engorged specimens was negatively impacted by the blood meal after frozen storage. The addition of specimens from Mali into the database significantly improved the results of Mali panel (p < 0.0001), which became comparable between head and legs. With higher identification scores, the using of the head will allow to decrease the number of technical replicates of protein extract per specimen, which represents a significant improvement for routine use of MALDI-TOF MS.ConclusionsThe using of the head of Anopheles may improve the performance of MALDI-TOF MS. Region-specific mass spectrum databases will have to be produced. Further research is needed to improve the standardization in order to share online spectral databases.
Highlights
Anopheles species identification is essential for an effective malaria vector control programme
The highest correlations between spectra were observed for the heads and thoraces, and the lowest correlations were observed for the legs
The head spectra from field-collected An. gambiae were the most reproducible compared to the thorax and the legs
Summary
Anopheles species identification is essential for an effective malaria vector control programme. Nabet et al Malar J (2021) 20:33 vector species identification [3]. It requires technical skills and comprehensive training. It is difficult for damaged specimens, new species, cryptic species, species with overlapping characteristics and cases of intraspecies morphological variation [4]. To overcome biased interpretations of species distributions and bionomics, molecular identification has been proposed as a complementary tool [5]. The most targeted gene for Anopheles species identification is the rDNA internal transcribed spacer region 2 (rDNA ITS2). Specific primers are often required for species identification, such as that for the Sundaicus complex [6]. Multiple gene sequences are often needed for unambiguous identification, especially due to poor availability of molecular reference databases [3, 7, 8]
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