# The first mitogenome of Petrovinema skrjabini from Equus ferus przewalskii: a phylogenetic analysis within the Strongylidae family

## TL;DR

This study reports the first complete mitochondrial genome of Petrovinema skrjabini, a parasitic nematode in horses, and uses it to clarify its evolutionary relationships within the Strongylidae family.

## Contribution

The first complete mitogenome of Petrovinema skrjabini is sequenced and used to revise phylogenetic relationships in Strongylidae.

## Key findings

- The P. skrjabini mitogenome is 13,885 base pairs with a high AT content of 75.4%.
- Phylogenetic analysis suggests Triodontophorus should be reclassified into the subfamily Cyathostominae.
- The study provides genetic markers for improved identification and taxonomy of P. skrjabini.

## Abstract

Petrovinema skrjabini (Nematoda: Strongylidae, Cyathostominae) is a parasitic nematode colonizing the cecum and colon of equids. Like other cyathostomins, its larvae (L3) invade the intestinal mucosa, forming encysted nodules that may remain dormant for years. Mass larval emergence triggers larval cyathostominosis—a severe syndrome characterized by hemorrhagic typhlocolitis and diarrhea, with mortality rates exceeding 50%. However, owing to the morphological indistinguishability of cyathostomin and frequent mixed infections in natural settings, species-specific contributions to pathogenesis remain unresolved. Previous studies on P. skrjabini have predominantly focused on its morphology, with limited molecular information available.

The complete mitogenome of Petrovinema skrjabini was sequenced using the Illumina NovaSeq 6000 platform, followed by assembly and annotation. We performed a phylogenetic analysis using Bayesian inference (BI) and maximum likelihood (ML) methods, based on 12 protein-coding genes from mitogenomes, to assess the evolutionary relationships of 34 Strongylidae species.

The complete mitogenome of P. skrjabini comprises 13,885 base pairs with 12 protein-coding genes, two ribosomal-RNA genes, 22 transfer-RNA genes, and two non-coding regions. The gene arrangement of the P. skrjabini mitogenome was consistent with the GA3 arrangement found in other Strongylidae species. The mitogenome exhibited a high AT bias (75.4%), which is consistent with other species in other Strongylidae species. Phylogenetic analysis showed that two Strongylus species (belonging to subfamily Strongylinae) formed a clade and located in the base of Strongylidae, while three Triodontophorus (belonging to subfamily Strongylinae) species and P. skrjabini formed another clade within in subfamily Cyathostominae within Strongylidae, based on 12 protein-coding genes from mitogenomes, suggesting that the genus Triodontophorus should transfer to the subfamily Cyathostominae.

The characterization of the complete mitochondrial genomes of P. skrjabini is reported for the first time. This study provided helpful genetic markers for P. skrjabini identification and taxonomy, facilitating early nematode diagnosis and treatment to decrease equine parasitic nematode burdens. Our mitochondrial phylogeny analyses further corroborate the hypothesis that the genus Triodontophorus belongs to Cyathostominae. The present study enriches the database of strongylids mitogenomes and provides a new insight into the systematics of the family Strongylidae.