Abstract
Vector control is the mainstay of malaria control programmes. Successful vector control profoundly relies on accurate information on the target mosquito populations in order to choose the most appropriate intervention for a given mosquito species and to monitor its impact. An impediment to identify mosquito species is the existence of morphologically identical sibling species that play different roles in the transmission of pathogens and parasites. Currently PCR diagnostics are used to distinguish between sibling species. PCR based methods are, however, expensive, time-consuming and their development requires a priori DNA sequence information. Here, we evaluated an inexpensive molecular proteomics approach for Anopheles species: matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). MALDI-TOF MS is a well developed protein profiling tool for the identification of microorganisms but so far has received little attention as a diagnostic tool in entomology. We measured MS spectra from specimens of 32 laboratory colonies and 2 field populations representing 12 Anopheles species including the A. gambiae species complex. An important step in the study was the advancement and implementation of a bioinformatics approach improving the resolution over previously applied cluster analysis. Borrowing tools for linear discriminant analysis from genomics, MALDI-TOF MS accurately identified taxonomically closely related mosquito species, including the separation between the M and S molecular forms of A. gambiae sensu stricto. The approach also classifies specimens from different laboratory colonies; hence proving also very promising for its use in colony authentication as part of quality assurance in laboratory studies. While being exceptionally accurate and robust, MALDI-TOF MS has several advantages over other typing methods, including simple sample preparation and short processing time. As the method does not require DNA sequence information, data can also be reviewed at any later stage for diagnostic or functional patterns without the need for re-designing and re-processing biological material.
Highlights
Human malaria is exclusively transmitted by Anopheles spp. mosquitoes
We recorded spectra from 320 laboratory specimens, including 32 Anopheles colonies and one Aedes aegypti colony (Table 1), and spectra from 125 field-caught specimens that included a mixture of sibling species and molecular forms from two field populations, ‘‘Soumousso’’ in Burkina Faso
The present study shows that MALDI-TOF mass spectrometry (MS) reliably discriminates between anopheline mosquito species - even at the sub-species level
Summary
Most key malaria mosquito vectors – and many other mosquito species - are members of complexes or groups comprising morphologically indistinguishable sibling species [1]. Fundamental for understanding vector biology; and malaria risk factors and epidemiology. A widely discussed case is the Anopheles gambiae Giles 1902 species complex comprising at least seven morphologically identical sibling species across Africa [2]. Two of the members of this complex, A. gambiae sensu stricto (s.s.) and A. arabiensis, are major malaria vectors in sub-Saharan Africa and are found in sympatry over a large geographical range [3]. For malaria epidemiology and vector control an important aspect is the fact that these species differ in their biology. Sympatric mosquito species may show different levels of susceptibility to available insecticides for mosquito control The M and S forms have been found to display different ecological tolerances and behaviours adding evidence of reproductive isolation between them [14,15,16,17,18]
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