Genetic diversity and molecular evolution of the internal transcribed spacer regions (ITS1–5.8S–ITS2) of Babesia vogeli

Abstract

Canine babesiosis, a severe haemoparasitic disease caused by Babesia species, has a significant global presence and can be fatal if left untreated. The current study was aimed to perform the population genetic characterization of B. vogeli on the basis of the internal transcribed spacer regions (ITS1–5.8S–ITS2). A maximum likelihood tree constructed with the Hasegawa-Kishino-Yano model grouped all sequences into a single major clade (BvG1), with the exception of a Taiwanese isolate (EF186914), which branched separately. This Taiwanese isolate represented a novel genotype (BvG2) identified in the present study. Nucleotide sequences (n = 62) exhibited 92.5–100 % nucleotide identity among themselves. However, the BvG1 and BvG2 genotypes shared a lower identity of 92.5–93.8 % between them. Notably, the newly generated Indian sequences (n = 21) demonstrated a high degree of homology, with 98.3–100 % identity. Alignment of the nucleotide sequences revealed 58 variations across the dataset. Additionally, 32 sites exhibited variation within the BvG1 genotype, while 56 sites differed between BvG1 and BvG2 genotypes. Within different B. vogeli populations, the nucleotide diversity (π) was low, but the haplotype diversity (Hd) was high. The haplotype diversity of the Indian population, BvG1 genotype, and the combined dataset was ∼0.8 suggesting a high haplotype diversity. The median-joining haplotype network displayed a total of 21 haplotypes, out of which six haplotypes consisted of more than one sequence (2–25 sequences). Haplotype distribution showed significant geographical structuring, with most haplotypes confined to a single country. Only two haplotypes (9.52 %; Hap_1 and Hap_4) were shared between countries, whereas 19 haplotypes (90.48 %) were country-specific. Hap_1, Hap_6, and Hap_4 were the most representative haplotypes, comprising 25, 10, and four sequences, respectively. India exhibited the highest number of haplotypes (h = 13) followed by China (h = 4), the United States of America (h = 3), Taiwan and Tunisia (h = 2), and Thailand (h = 1). Both location-wise and genotype-wise median joining haplotype networks clustered the haplotypes in two groups, representing two distinct genotypes (BvG1 and BvG2). The B. vogeli populations between Thailand and Tunisia exhibited the highest genetic differentiation (FST = 0.80) with a low gene flow (Nm = 0.125) between them. Results of AMOVA revealed a higher genetic variation within populations (69.43 %) as compared to the variation between them (30.57 %). Neutrality indices and the mismatch distributions of the Indian population and the overall dataset of B. vogeli indicated a constant population size to population expansion and population expansion, respectively, with the presence of two distinct genotypes. These data provide information about parasite population genetics and highlight the importance of starting a long-term molecular surveillance program. In conclusion, a high genetic diversity along with the presence of two distinct genotypes of B. vogeli were observed on the basis of internal transcribed spacer regions (ITS1–5.8S–ITS2).