[Population genetic structure of sandflies in China based on mitochondrial DNA].

Abstract

Objective: To investigate the genetic diversity of sandfly populations in endemic areas of visceral leishmaniasis in China, so as to provide references insights into management of visceral leishmaniasis and the vector sandflies.

Methods: Sixteen sampling sites were selected from main endemic foci of visceral leishmaniasis in China from June to September 2024, including Shanxi Province, Shaanxi Province, Henan Province, Gansu Province, Sichuan Province, and Xinjiang Uygur Autonomous Region. Sandflies were captured using light traps and manual aspirators from sheep pens, chicken coops, cave dwellings, bovinesheds, and pig pens at each sampling site. A single sandfly sample was washed in phosphate-buffered saline (PBS), and genomic DNA was extracted from sandfly samples. Cytochrome oxidase subunit 1 (COI) gene was amplified using PCR assay with universal primers, and analyzed and retrieved with the nucleotide sequence analysis tool (BLAST) software, and the sequence of COI gene was aligned with the ClustalX 1.83 and MEGA 7.0 software. The base composition and variation site of the COI gene sequence were analyzed using the software MEGA 7.0, and the number of haplotypes, total number of segregating sites, haplotype diversity, nucleotide diversity, and average nucleotide differences were calculated in the COI gene sequence using the software DnaSP 5.10, followed by Tajima's D test for neutrality. Haplotypes were screened using the software DnaSP 5.10, and the haplotype network map of sandfly samples was plotted using the software Network 5.0. MEGA 7.0 software was employed for gene sequence editing and alignment, and calculation of genetic distances among sandfly species sampled from different regions, and a phylogenetic tree was built with a neighbor-joining method.

Results: A total of 466 sandflies were captured from 16 sampling sites in China from June to September 2024, and 430 gene sequences were yielded following PCR amplification and sequencing of the COI gene, with 652 to 688 bp in the length of amplification fragments. The captured sandfly samples were characterized as Phlebotomus chinensis, Sergentomyia squamirostris, Se. koloshanensis, Ph. sichuanensis, and Ph. longiductus following the COI gene sequence alignment in BLAST. A total of 251 haplotypes were identified in the 430 gene sequences from sandfly samples (50.5%), and the average haplotype diversity, nucleotide diversity and average number of nucleotide difference were 0.885, 0.257 and 160.761, respectively. The Tajima's D values were -0.92 for sandfly populations from Yangquan City, Shanxi Province and -1.73 for sandfly populations from Sanmenxia City, Henan Province, and were all more than 0 for sandfly populations from other sampling sites. Haplotype analysis identified 50 haplotypes, which were classified into two haplogroups. Heplogroup 1 included 29 haplotypes, which had a high homology, and heplogroup 2 included 21 haplotypes. The average genetic distance was 0.000 to 0.604 among sandfly samples from different sampling sites, and phylogenetic analysis revealed that the five sandfly species were clustered into distinct clades, all with 100% clade confidence.

Conclusions: There is a high genetic polymorphism in the COI gene from five sandfly populations in main endemic foci of visceral leishmaniasis in China, and COI gene may serve as a marker gene for analysis of the genetic structure of sandfly populations.