Cladistics of Echinococcus granulosus Sensu Stricto Genotypes Infecting the Slaughtered Pigs

Echinococcus granulosus sensu stricto (s. s.) consists of the most widespread genotypes (G1, G3) implicated in human cystic echinococcosis worldwide. The present study aimed to evaluate the role of pigs in the transmission dynamics of E. granulosus s. s. genotypes, including the phylogenetics, evolutionary divergence and haplotype network analyses of north Indian pig isolates along with GenBank^™ archived sequences.

In totality, 223 slaughtered pigs were thoroughly screened for the presence of hydatid cysts. The amplification of the partial mitochondrial cytochrome C oxidase subunit 1 gene was performed for the molecular confirmation and phylogenetics of the retrieved metacestodes.

The molecularly confirmed and sequenced present study isolates (n = 2) clustered with the E. granulosus genotype G3. The very low evolutionary divergence values (< 0.0027) of the present study isolates with E. ganulosus genotype G3 indicated the absence of diverged lineages. The significantly negative values of Tajima's D (- 2.598) and Fu and Li's D (- 4.054) of the overall dataset and for the Asian sequences signified an expansion of population size. The overall dataset exhibited low nucleotide (0.067 ± 0.055) and high haplotype (0.574 ± 0.015) diversities, also alluding to demographic expansion. The haplotype network showed that the pig isolates from South America and Europe constituted the predominant haplotype, Hap_2 along with Hap_3 and Hap_6, primarily associated to E. granulosus genotype G1; whereas, the Indian isolates formed different haplotypes (Hap_1 and Hap_5) belonging to genotype G3.

The present study highlighted the important role of pigs in the transmission of E. granulosus s. s., which is of paramount significance given the public health and economic impact of cystic echinococcosis.