Molecular identification of the potential fifth species within genus Hydatigera (Cestoda: Taeniidae) in rodents of Guangdong province, China

<i>Hydatigera</i> (Cestoda: Taeniidae) is a recently resurrected genus based on molecular data, comprising only four valid species: <i>Hydatigera taeniaeformis</i>, <i>Hydatigera krepkogorski</i>, <i>Hydatigera parva</i>, and <i>Hydatigera kamiyai</i>. In this study, a total of 479 rodents were collected. In total, 46 livers with visible cysts were observed from five species of rodents collected in three locations of Guangdong province, China, in 2023. Molecular analysis utilizing 18S rRNA sequences indicated that 38 of the 46 liver cysts were infected by <i>Hydatigera</i>, suggesting that this genus represents the predominant tapeworm responsible for the visible liver cysts in rodents. Metagenomic next-generation sequencing (mNGS) was further used to obtain the mitochondrial genomes of these tapeworms. Phylogenetic analyses based on the 12 protein-coding genes (PCGs) and 18S rRNA both demonstrated the formation of two distinct clades: one comprising <i>H. taeniaeformis</i>, and the other representing a novel clade that is positioned as the sister clade to <i>H. kamiyai</i>, exhibiting genetic distance of 11.91 %-12.38 % for the 12 PCGs and 3.22 %-5.25 % for the 18S rRNA. Given the deep inter-species genetic distance, the novel clade identified in this study may be the fifth species within the genus <i>Hydatigera</i>, designated as <i>Hydatigera</i> sp. Both <i>H. taeniaeformis</i> and <i>Hydatigera</i> sp. were found to utilize not only wild rodents (<i>N. huang</i>, <i>N. niviventer</i> and <i>R. andamanensis</i>) but also house rats (<i>R. norvegicus</i> and <i>R. tanezumi</i>) as intermediate hosts. This finding indicates that they may have both sylvatic and synanthropic transmission cycles, raising concerns regarding their potential threat to humans and domestic animals.