Exploring the utility of phylogenetic analysis of cytochrome oxidase gene subunit I as a complementary tool to classical taxonomical identification of phlebotomine sand fly species (Diptera, Psychodidae) from southern Europe

Identification of wild-caught phlebotomine sand flies from Crete and Cyprus using DNA barcoding

Background

Phlebotomine sand flies (Diptera: Psychodidae) are vectors of Leishmania spp., protozoan parasites responsible for a group of neglected diseases called leishmaniases. Two sand fly genera, Phlebotomus and Sergentomyia, contain species that are present in the Mediterranean islands of Crete and Cyprus where the visceral (VL), cutaneous (CL) and canine (CanLei) leishmaniases are a public health concern. The risk of transmission of different Leishmania species can be studied in an area by monitoring their vectors. Sand fly species are traditionally identified using morphological characteristics but minute differences between individuals or populations could be overlooked leading to wrong epidemiological predictions. Molecular identification of these important vectors has become, therefore, an essential tool for research tasks concerning their geographical distribution which directly relates to leishmaniasis control efforts. DNA barcoding is a widely used molecular identification method for cataloguing animal species by sequencing a fragment of the mitochondrial gene encoding cytochrome oxidase I.

Results

DNA barcoding was used to identify individuals of five sand fly species (Phlebotomus papatasi, P. similis, P. killicki, Sergentomyia minuta, S. dentata) circulating in the islands of Crete and Cyprus during the years 2011–2014. Phlebotomus papatasi is a known vector of zoonotic CL in the Middle East and it is found in both islands. Phlebotomus similis is the suspected vector of Leishmania tropica in Greece causing anthroponotic CL. Phlebotomus killicki was collected in Cyprus for the first time. Sergentomyia minuta, found to present intraspecific diversity, is discussed for its potential as a Leishmania vector. Molecular identification was consistent with the morphological identification. It successfully identified males and females, which is difficult when using only morphological characters. A phylogenetic tree was constructed based on the barcodes acquired, representing their genetic relationships along with other species from the area studied. All individuals identified were clustered according to their species and subgenus.

Conclusions

Molecular identification of sand flies via DNA barcoding can accurately identify these medically important insects assisting traditional morphological tools, thus helping to assess their implication in Leishmania transmission.

DNA sequencing confirms PCR-RFLP identification of wild caught Larroussius sand flies from Crete and Cyprus

Many Phlebotomine sand fly species (Diptera, Psychodidae) are vectors of the protozoan parasite Leishmania causing a group of diseases called the leishmaniases. The subgenus Larroussius includes sand fly vectors found in South East Mediterranean Basin responsible for Visceral (VL) and Cutaneous human leishmaniasis (CL). It is important to monitor these medically important insects in order to safely predict possible Leishmania transmission cycles. Leishmania infantum is endemic in the islands of Crete and Cyprus with increasing VL cases in humans and dogs and in Cyprus the newly introduced Leishmania donovani causes both VL and CL in humans. The morphological identification of the females of the subgenus Larroussius often presents difficulties. Morphology and COI PCR - RFLP were used to identify wild caught Larroussius sand flies belonging to Phlebotomus tobbi, P. perfiliewi, and P. neglectus species from Crete and Cyprus. The identification results were further confirmed by sequencing (DNA barcoding) and Bayesian phylogenetic analysis. COI PCR - RFLP, when correctly optimized and with respect to geographical origin, can serve as an initial patterning identification tool when large sand fly numbers need to be identified. It could accurately assign Larroussius females and males to their taxa overcoming the difficulties of morphological identification. Finally, DNA barcoding will contribute to a molecular identification database to be used for in-depth species studies.

Vector soup: high-throughput identification of Neotropical phlebotomine sand flies using metabarcoding

Phlebotomine sand flies are haematophagous 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. Here, we assessed the reliability of a short insect metabarcode located in the mitochondrial 16S rRNA for the identification of Neotropical sand flies, and constructed a reference database for 40 species found in French Guiana. Then, we conducted a metabarcoding experiment on sand flies mixtures of known content and showed that the method allows an accurate identification of specimens in pools. Finally, we applied metabarcoding to field samples caught in a 1-ha forest plot in French Guiana. Besides providing reliable molecular data for species-level assignations of phlebotomine sand flies, our study proves the efficiency of metabarcoding based on the mitochondrial 16S rRNA for studying sand fly diversity from bulk samples. The application of this high-throughput identification procedure to field samples can provide great opportunities for vector monitoring and eco-epidemiological studies.

Species composition, activity patterns and blood meal analysis of sand fly populations (Diptera: Psychodidae) in the metropolitan region of Thessaloniki, an endemic focus of canine leishmaniasis

Species composition, activity patterns and blood meal analysis of sand fly populations were investigated in the metropolitan region of Thessaloniki, North Greece from May to October 2011. Sampling was conducted weekly in 3 different environments (animal facilities, open fields, residential areas) along the outskirts of the city in areas of increased canine leishmania transmission. Six sand fly species (Phlebotomus perfiliewi, Phlebotomus tobbi, Phlebotomus simici, Plebotomus papatasi, Sergentomya minuta and Sergentomya dentata) were identified using both classical and molecular techniques. DNA barcodes were characterized for the first time for two (P. simici and S. dentata) of the six recorded species. Phylogenetic analysis based on the COI gene sequences confirmed the grouping of P. tobbi, P. perniciosus and P. perfiliewi (subgenus Larrousius) and the monophyly of P. simici (subgenus Adlerius). By far the most prevalent species was P. perfiliewi, followed by P. simici and P. tobbi. The largest populations of sand flies were collected from animal facilities, followed by residential areas and open agricultural fields. Peak activity of sand flies overall occurred mid-August to mid-September and then declined sharply in October. Blood meal analysis showed that P. perfiliewi and P. simici feed preferentially on humans (88% & 95%, respectively) but also feed on chickens and goats. When designing a control strategy to alleviate sand fly nuisance in the region of Thessaloniki the following conclusions can be reached from this study: a) August and September are high risk months due to increased sand fly activity levels, b) animal facilities within or adjacent to urban settlements are high risk areas and may act as a maintenance and amplification foci for the vector as well as the parasite, and c) the abundance, ubiquity and feeding behavior of P. perfiliewi and P. simici establishes them as potentially important vectors of Leishmania in the region.

Mild-Vectolysis: A Nondestructive DNA Extraction Method for Vouchering Sand Flies and Mosquitoes

Nondestructive techniques allow the isolation of genomic DNA, without damaging the morphological features of the specimens. Though such techniques are available for numerous insect groups, they have not been applied to any member of the medically important families of mosquitoes (Diptera: Culicidae) and phlebotomine sand flies (Diptera: Psychodidae). This study presents Mild-Vectolysis, the first nondestructive DNA extraction methodology for vouchering taxa of mosquitoes and sand flies, which provided sufficient amounts of DNA, tested in a verified barcode (cytochrome oxidase I gene), while preserving their morphological integrity. Application of the method to sand flies allowed successful insect identification post DNA extraction, as all basic taxonomical structures necessary for identification (pharynx, cybarium, and genitalia) remained intact. The development of the methodology was more challenging in mosquitoes, due to the fragility of key morphological characters (scales and color). A small modification of the lysis buffer concentration, in combination with the adjustment of the incubation time, a postlysis freezing stage, and the avoidance of ethanol, achieved the extraction of sufficient DNA quantity, while preserving the integument of the mosquitoes, although a small proportion of the scales and the color still appeared to have been lost. In addition to the practicality and efficiency of our methodology, preserving of the original insect specimen post DNA extraction is highly advantageous, as it allows for 1) utilization of the specimen for further analysis and 2) storage for vouchering.