Time-series transcriptomic profiling of larval exsheathment in a model parasitic nematode of veterinary importance

Haemonchus contortus (barber’s pole worm), is one of the most economically important pathogenic nematodes that attacks small ruminants, such as sheep and goats, representing a global animal health issue through drastic losses in livestock. The life cycle of this nematode is comprised of six stages, namely, eggs, first to fourth stage larvae (L1, L2, L3 and L4) and adults (Veglia, 1915). In Haemonchus contortus and related nematodes, infective L3s are ingested by the host and enter the rumen where larval exsheathment occurs that marks the transition from the free-living to the parasitic stages of these parasites (Rogers, 1960). Molecular and omics driven studies targeting this key transition phase can help us understand the developmental physiology of this model nematode which can be used to develop both biological and biotechnological control strategies in the future.

There have been earlier transcriptomic and expressed sequence tag (EST) studies describing the differences in transcription between free-living infective (iL3) and parasitic (xL3) third-stage larvae of H. contortus (Cantacessi et al., 2010; Laing et al., 2013; Schwarz et al., 2013). However, a major knowledge gap remains amongst the available RNA-seq data sets for this parasitic nematode (Jex et al., 2019). However, all these studies applied the common laboratory practice of the utilization of sodium hypochlorite as the desheathment agent. Recently, a closed in vitro parasite culture system that effectively mimics rumen conditions to effectively stimulate exsheathment without chemical interventions has been reported (Bekelaar et al., 2018; Palevich et al., 2022; Palevich et al., 2023a). Briefly, this system involves an increase to rumen temperature (39°C) and a strictly anaerobic environment of predominantly carbon dioxide (CO2). The larval exsheathment method used in this study for an RNA-seq approach, has recently been validated as an adaptable technique for multi-omic’ applications of H. contortus (Palevich et al., 2022). The aim of our study was to provide the scientific community a detailed time-series transcriptomic description of natural larval exsheathment of H. contortus, a valuable resource for future multiomics functional studies investigating larval exsheathment and parasite development.