Tuesday, June 21, 2016

Phlebotomine sand fly identification using HTS

Lutzomyia longipalpis
Phlebotomine sand flies are hematophagous dipterans of primary medical importance. They
represent the only proven vectors of leishmaniasis worldwide and are involved in the transmission of various other pathogens. Studying the ecology of sand flies is crucial to understand the epidemiology of leishmaniasis and further control this disease. A major limitation in this regard is that traditional morphological-based methods for sand fly species identifications are time-consuming and require taxonomic expertise. DNA metabarcoding holds great promise in overcoming this issue by allowing the identification of multiple species from a single bulk sample. 

According to the WHO about 12 million people worldwide are currently infected with Leishmania. Each year about 20000 - 50000 people die from the disease and 2 million new cases are reported annually. About 200 million people live in areas where the disease is common. The disease is transmitted by the bite of infected female phlebotomine sandflies which can transmit the protozoan.

The sandfly genus Lutzomyia genus currently includes 477 described species, among which 56 are proven or suspected vectors of Leishmania. A new study of colleagues from France and French Guiana now assessed the reliability of mitochondrial 16S rRNA sequences using paired-end sequencing on a MiSeq platform. They call their approach metabarcoding but I beg to differ as 16S is not a barcode marker for animals. Not sure what to call it and I also disagree with their assessment that  the standard COI barcode is however not well suited for metabarcoding applications. There are a number of good studies that show that this claim is rather premature. The authors actually suggest the construction of a further reference library for 16S rRNA. 

Nevertheless, the study as such is very good. It is based on a newly constructed reference database for 40 species found in French Guiana. The colleagues successfully experimented with sand flies mixtures of known content and with field samples caught in a 1 ha forest plot in French Guiana. Given the serious basis for the study every progress in species identification should first and foremost be considered a very positive development and disagreement on markers is rather a question of efficiency and community standards but one that should be discussed further.

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