Abstract
Ascaridoid nematodes are widespread in marine fishes. Despite their major socioeconomic importance, mechanisms associated to the fish-borne zoonotic disease anisakiasis are still obscure. RNA-Seq and de-novo assembly were herein applied to RNA extracted from larvae and dissected pharynx of Hysterothylacium aduncum (HA), a non-pathogenic nematode. Assembled transcripts in HA were annotated and compared to the transcriptomes of the zoonotic species Anisakis simplex sensu stricto (AS) and Anisakis pegreffii (AP). Approximately 60,000,000 single-end reads were generated for HA, AS and AP. Transcripts in HA encoded for 30,254 putative peptides while AS and AP encoded for 20,574 and 20,840 putative peptides, respectively. Differential gene expression analyses yielded 471, 612 and 526 transcripts up regulated in the pharynx of HA, AS and AP. The transcriptomes of larvae and pharynx of HA were enriched in transcripts encoding collagen, peptidases, ribosomal proteins and in heat-shock motifs. Transcripts encoding proteolytic enzymes, anesthetics, inhibitors of primary hemostasis and virulence factors, anticoagulants and immunomodulatory peptides were up-regulated in AS and AP pharynx. This study represents the first transcriptomic characterization of a marine parasitic nematode commonly recovered in fish and probably of negligible concern for public health.
Highlights
Nematodes belonging to the genera Hysterothylacium (Ascaridoidea: Raphidascarididae) and Anisakis (Ascaridoidea: Anisakidae) are heteroxenous parasites widely found in several marine aquatic organisms [1,2,3,4]
Some attempts have been made to clarify some aspect of infection using in-vivo tests with animal models [19] or to explore human immune responses using in-vitro systems [33], suggesting a general strong induction of immune reaction
We provide the first characterization of the entire set of molecules transcribed by the whole larva and pharyngeal tissue of Hysterothylacium aduncum, an ascaridoid nematode species related to anisakids, widely distributed in fishes
Summary
Nematodes belonging to the genera Hysterothylacium (Ascaridoidea: Raphidascarididae) and Anisakis (Ascaridoidea: Anisakidae) are heteroxenous parasites widely found in several marine aquatic organisms [1,2,3,4]. Their life cycles are indirect and complex, based on prey-predator relations. Adults of the genus Hysterothylacium are common parasites of predatory teleosts, whilst various species of marine fishes act as intermediate hosts by harboring larval stages that are infective to their definitive hosts [5]. Definitive and intermediate hosts of Anisakis are marine mammals and crustaceans, respectively, while fishes and squids can act as paratenic hosts [2]. The majority of the larvae are located in the visceral body cavity of infected fish; seldom larvae may migrate to the flesh fillets, sometimes before the death of the host [6].
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