Rickettsial agents detected in the genus Psathyromyia (Diptera:Phlebotominae) from a Biosphere Reserve of Veracruz, Mexico

Assessing Wolbachia circulation in wild populations of phlebotomine sand flies from Spain and Morocco: implications for control of leishmaniasis

BACKGROUND

Vector-borne diseases such as leishmaniasis exert a huge burden of morbidity and mortality that are mainly controlled through vector control. The increasing threat of insecticide-resistant vectors entails incorporating more vector control interventions to eliminate these diseases. Introduction of Wolbachia into wild vector populations has been suggested as a potential vector control measure that would require extensive regional knowledge. The aim of this work is to estimate the prevalence of Wolbachia infection and monitor circulating strains in wild sand fly populations from Spain and Morocco, two countries where leishmaniasis is endemic.

METHODS

Wolbachia was detected using polymerase chain reaction (PCR). Haplotype diversity was performed by sequencing, and phylogenetic relationships were then established. In silico prediction of the Wolbachia surface protein (WSP) structures was performed. To investigate the relationship between epidemiological variables and the presence of Wolbachia, regression analyses were employed.

RESULTS

Wolbachia was detected in 45.8% of the specimens tested (319/697), and similar infection rates were found (P = 0.92) in males (46.1%; 94/204) and females (45.6%; 225/493). Differences in infection were detected among Spanish sand fly species (P < 0.001), being higher for Phlebotomus papatasi (35/52) and Phlebotomus perniciosus (239/384). No infected Phlebotomus sergenti specimens were found in Spain, whereas two different Wolbachia haplotypes were detected in P. sergenti sand flies from Morocco. No significant differences were found between sex, species, or capture sites in specimens captured in Morocco (P > 0.05). Five Wolbachia haplotypes distributed in the known A and B supergroups were identified. Structural analysis showed a nine-amino acid insertion in the fourth loop of a Wolbachia haplotype found in P. sergenti specimens from El Borouj (Morocco).

CONCLUSIONS

We confirmed the circulation of different Wolbachia strains in all sand fly species investigated. All L. infantum proven or suspected vectors shared the same, or a closely related, Wolbachia haplotype. The haplotype bearing the loop insertion was found in the locality undergoing an anthroponotic cutaneous leishmaniasis outbreak. These extracellular loops might have some role in enhancing or inhibiting the development of Leishmania and other pathogens in sand flies. These findings are very promising and highlight the need to further investigate the tripartite interactions between Wolbachia strain, Leishmania species, and sand fly species/lineage.

Interaction and effects of temperature preference under a controlled environment on the diversity and abundance of the microbiome in Lutzomyia longipalpis (Diptera: Psychodidae)

Characterization of the temperature effects on the abundance and richness of the microbiota of Lutzomyia longipalpis, insect vector of Leishmania infantum in America, is an aspect of pivotal importance to understand the interactions between temperature, bacteria, and Leishmania infection. We developed and used a customized device with a temperature gradient (21-34 °C) to assess the temperature preferences of wild females of Lu. longipalpis collected in a rural area (Ricaurte, Cundinamarca, Colombia). Each replicate consisted of 50 females exposed to the gradient for an hour. At the end of the exposure time, insects were collected and separated by the temperature ranges selected varying from 21 °C to 34 °C. They were organized in 17 pools from which total DNA extracts were obtained, and samples were subjected to 16S rRNA amplicon sequencing analyzes. The most abundant phyla across the different temperature ranges were Proteobacteria (17.22-90.73 %), Firmicutes (5.99-77.21 %) and Actinobacteria (1.56-59.85 %). Results also showed an abundance (30 % to 57.36 %) of Pseudomonas (mainly at temperatures of 21-29 °C and 34 °C) that decreased to 6.55 %-13.20 % at temperatures of 31-33 °C, while Bacillus increase its abundance to 67.24 % at 29-33 °C. Serratia also had a greater representation (49.79 %), specifically in sand flies recovered at 25-27 °C. No significant differences were found at α-diversity level when comparing richness using the Shannon-Wiener, Simpson, and Chao1 indices, while β-diversity differences were found using the Bray-Curtis index (F-value of 3.5073, p-value < 0.013, R-squared of 0,4889), especially in the groups of Lu. longipalpis associated at higher temperatures (29-33 °C). It was also possible to detect the presence of endosymbionts such as Spiroplasma and Arsenophonus in the range of 29-33 °C. Rickettsia was only detected in Lu. longipalpis sand flies recovered between 25-27 °C. It was possible to characterize Lu. longipalpis microbiota in response to intraspecific temperature preferences and observe changes in bacterial communities and endosymbionts at different ranges of said environmental variable, which may be important in its vector competence and environmental plasticity to adapt to new climate change scenarios.

New status of Bichromomyia subspecies (Diptera: Psychodidae: Phlebotominae) based on molecular taxonomy

The sand fly of the genus Bichromomyia (Galati, 1995) includes 3 subspecies considered vectors of Leishmania, which share high morphological similarity. Through information from the Cytochrome Oxidase Subunit I (COI) gene, we provide complementary evidence to support that Bichromomyia olmeca olmeca, and Bichromomyia olmeca bicolor, should be raised to nominal species status. We recovered specimens of Bi. o. olmeca from Quintana Roo, Tabasco, and Oaxaca, Mexico, supply 17 new COI sequences, and also incorporate GenBank sequences for other Bichromomyia species. After a Maximum Likelihood (ML) analysis, all Bichromomyia species clustered with a bootstrap of 100%, although sequences of Bichromomyia flaviscutellata were divided into 2 clusters with an interspecific range distance of 11.16% between them, which confirm cryptic species in Brazil. The genetic distance of Bi. o. olmeca compared to related subspecies ranged between 12.59% and 14.64%. A total of 29 haplotypes (Hd = 0.987; π = 0.08783; S = 136) were recovered from the Bichromomyia sequences. Results of the TC network were consistent with the ML analysis, supporting that subspecies of Bichromomyia are genetically distinct and deserve being raised to valid species category: Bichromomyia olmeca (Vargas & Díaz-Nájera) and Bichromomyia bicolor (Fairchild & Theodor).

Species diversity and detection of pathogens in phlebotomine sand flies collected from forest management areas of Quintana Roo, Mexico

Sand flies have expanded their areas of distribution, thereby increasing the risk of pathogen transmission in non-endemic areas. To establish efficient prevention and control strategies for the transmission of vector-borne pathogens, it is important to understand seasonal dynamics of their vectors. In Mexico, there are several areas where the contact between sand flies, hosts and reservoirs favours the transmission of the pathogen. We compared sand fly communities in a forest management area and a conserved area in Noh-Bec, Quintana Roo, Mexico. The analysis included species diversity, activity peaks and molecular detection of pathogens. Sand flies were collected from November to December 2021 and April to May 2022, during 84 night-traps. The conserved area showed higher numbers and greater species heterogeneity of sand flies as compared with the other sites. The β-diversity analysis revealed that sites disturbed by logging (S1, S2, S3) had greater similarity (90%) in their sand fly species composition than a conserved area (S4) (similarity = 36%). Although none of the specimens were infected with Leishmania, we detected Wolbachia (19.4%) in all four sites, as well as Bartonella (3.25%) only in the disturbed sites. Further studies on the dynamics of sand fly populations and their association with pathogens are necessary.

Phylogenetic relations among Mexican phlebotomine sand flies (Diptera: Psychodidae) and their divergence time estimation

Phlebotomine sand flies (Diptera: Psychodidae: Phlebotominae) have biological relevance as vectors of several pathogens. To ensure periodic entomological monitoring it is necessary to have efficient and accurate tools for an adequate taxonomic identification. There are only few studies on phylogenetic analyses of phlebotomine sand flies from Neotropics, based mostly on morphological and/or molecular data, which makes the delimitation of intra- and interspecific variability of species challenging. Here we generated new molecular information on sand fly species distributed in endemic areas of leishmaniasis in Mexico, using mitochondrial and ribosomal genes, and incorporating morphological information available. Specifically, we established their phylogenetic relationships, and estimated their divergence time. Our study provides molecular information for 15 phlebotomine sand fly species from different areas of Mexico, contributing to the genetic inventory and phylogenetic relations among Neotropical species of the subfamily Phlebotominae. Mitochondrial genes proved to be suitable markers for the molecular identification of phlebotomine sand flies. However, the incorporation of additional nuclear gene information could increase the significance of phylogenetic inferences. We also provided evidence about a possible divergence time of phlebotomine sand fly species, supporting their presumable origin in the Cretaceous period.

Detection of Wolbachia and Leishmania DNA in sand flies (Diptera: Psychodidae, Phlebotominae) from a focus of cutaneous leishmaniasis in Tabasco, Mexico

Phlebotomine sand flies are the main vectors of Leishmania genus species worldwide; therefore, the detection of some reproductive parasites, such as Wolbachia, has been considered a possible strategy for biological control. In Mexico, leishmaniasis cases have been recorded in 25 states, yet only two sand fly species have been related to Wolbachia spp. Although the state of Tabasco has a high number of leishmaniasis cases, only few studies have been done on sand fly species. The aim of this study was to analyze the diversity of sand fly species and to detect Wolbachia spp. and/or Leishmania spp. in the captured specimens. Sand flies were collected at the locality of Huimango, Tabasco, Mexico, during October 2019, using nine light traps (CDC) and two Shannon traps per night. The specimens were identified and females were analyzed by PCR for the DNA detection for pathogens. A total of 193 sand fly specimens belonging to five species were morphologically identified. Pintomyia ovallesi was the most abundant species (76.84%), followed by Micropygomyia cayennensis (6.40%). Furthermore, first records of four sand fly species were established for the state of Tabasco, thereby increasing the species richness in the state from four to eight. We observed a natural infection rate of 9.7% (10/103) for Leishmania and 0.91% (1/103) for Wolbachia. The importance of conducting entomological surveys in endemic areas of leishmaniasis in Mexico is highlighted, to determine whether other sand fly species may be potential vectors of Leishmania spp., and if some Wolbachia strains could be relevant for the control of leishmaniasis.