Molecular Survey and Genetic Characterization of Hard Ticks from Chongming Island of Shanghai, China, Based on Mitochondrial Genome Fragments

Abstract

Abstract Background Ticks have been reported across China, but information on ticks from Chongming Eco-Island of Shanghai is lacking. Understanding the distribution and genetic evolution of ticks on the island is crucial for tick-borne infection control. Methods Ticks were collected from eight towns and four protected areas of Chongming Island during April 2021-March 2022 and were morphologically identified under microscopy. Molecular characterization of the ticks was performed by PCR amplification and sequencing of 12S rRNA and co1 mitochondrial genes. Homology analyses with published sequences obtained from GenBank were conducted for genetic relationships based on neighbor-joining (NJ) analysis of the 12S rRNA and co1 gene loci. To assess genetic evolution, intraspecific and interspecific genetic distances and barcoding gap were assessed based on NJ-K2P analysis of the 12S rRNA locus. Furthermore, genetic diversity and neutrality tests were performed on 12S rRNA sequences. Results A total of 1417/1933 ticks were successfully amplified by PCR of the 12S rRNA and co1 loci. Sequencing and homology analyses revealed four species of ticks, including Haemaphysalis flava (1376/1417 [97.11%], Ha. longicornis (37/1417 [2.61%]), Ha. doenitzi (3/1417 [0.21%]), and Ha. japonica (1/1417 [0.07%]). The intraspecies identity was 100% for Ha. longicornis, 99.11% for doenitzi, and 96.17%, while Ha. japonica had 83.48% intraspecies identity. Phylogenetic analyses showed species specificity, which clustered with homologous sequences. The average K2P distances between and within the species were 0.1351 (range 0.0723–0.1960) and 0.0145 (range 0-0.0946), respectively. The maximum K2P distance within species was in Ha. japonica (0.0946), while the maximum interspecific K2P distance was 0.1960 between Ha. hystricis and Ha. japonica. Genetic diversity indices and neutrality tests revealed that Fu and Li’s D and Tajima’s D values were negative for all species (mean values − 0.9360 and − 1.0310, respectively), suggesting evidence of recent population expansion. Conclusions This study is the first to report the genetic characterization of ticks from Chongming Eco-Island of Shanghai. We identified four species of Haemaphysalis ticks that were genetically similar to other congeners reported in China or worldwide. The knowledge gained from this study serves as a basis to support intervention deployment for effective control of tick-borne infections.