Trichinella spiralis secretes abundant unencapsulated small RNAs with potential effects on host gene expression

Many organisms, including parasitic nematodes, secrete small RNAs into the extracellular environment largely encapsulated within small vesicles. Parasite secreted material often contains microRNAs (miRNAs), raising the possibility that they might contribute to pathology by regulating host genes in target cells. Here we characterise material from the parasitic nematode Trichinella spiralis at two different life stages. We show that adult T. spiralis, which inhabit intestinal mucosa, secrete miRNAs within vesicles. Unexpectedly however, T. spiralis muscle stage larvae (MSL), which live intracellularly within skeletal muscle cells, secrete miRNAs that appear not to be encapsulated. Notably, secreted miRNAs include a homologue of mammalian miRNA-31, which has an important role in muscle development. Our work therefore suggests a new potential mechanism of RNA secretion with implications for the pathology of T. spiralis infection.