Helminth parasites secrete extracellular vesicles (EVs) that can be internalised by host immune cells resulting in modulation of host immunity. While the molecular cargo of EVs have been characterised in many parasites, little is known about the surface-exposed molecules that participate in ligand-receptor interactions with the host cell surface to initiate vesicle docking and subsequent internalisation. Using a membrane-impermeable biotin reagent to capture proteins displayed on the outer membrane surface of two EV sub-populations (termed 15k and 120k EVs) released by adult F. hepatica, we describe 380 surface proteins including an array of virulence factors, membrane transport proteins and molecules involved in EV biogenesis/trafficking. Proteomics and immunohistochemical analysis show that the 120k EVs have an endosomal origin and may be released from the parasite via the protonephridial (excretory) system whilst the larger 15k EVs are released from the gastrodermal epithelial cells that line the fluke gut. A parallel lectin microarray strategy was used to profile the topology of major surface oligosaccharides of intact fluorogenically-labelled EVs as they would be displayed to the host. Lectin profiles corresponding to glycoconjugates exposed on the surface of the 15 K and 120K EV sub-populations are practically identical but are distinct from those of the parasite surface tegument, although all are predominated by high mannose sugars. We found that while the F. hepatica EVs were resistant to exo- and endo-glycosidases, the glyco-amidase PNGase F drastically remodelled the surface oligosaccharides and blocked the uptake of EVs by host macrophages. In contrast, pre-treatment with antibodies obtained from infected hosts, or purified antibodies raised against the extracellular domains of specific EV surface proteins (DM9-containing protein, CD63 receptor and myoferlin), significantly enhanced their cellular internalisation. This work highlights the diversity of EV biogenesis and trafficking pathways used by F. hepatica and sheds light on the molecular interaction between parasite EVs and host cells.

Whilst historically regarded as being of minor importance in European livestock, recent evidence suggests that the prevalence of paramphistomosis is greater than that of fasciolosis in parts of the UK. In order to address this emerging threat to ruminant farming systems, and associated risks for food security posed by rumen fluke infection, it is imperative that we develop a better understanding of the basic biology of this parasite and how it interacts with its ruminant host. In this Opinion article we review recent progress in tracking the spread of rumen fluke infection in Europe, and propose some research questions that should be addressed if we are to develop tools to diagnose and treat paramphistomosis more effectively in the future.

This study aimed to determine the microbial composition of faeces from two groups of caecotrophagic animals; rabbits and guinea pigs. In addition the study aimed to determine the community present in the different organs in the rabbit. DNA was extracted from seven of the organs in wild rabbits (n = 5) and from faecal samples from domesticated rabbits (n = 6) and guinea pigs (n = 6). Partial regions of the small ribosomal sub-unit were amplified by PCR and then the sequences present in each sample were determined by next generation sequencing. Differences were detected between samples from rabbit and guinea pig faeces, suggesting that there is not a microbial community common to caecotrophagic animals. Differences were also detected in the different regions of the rabbits’ digestive tracts. As with previous work, many of the organisms detected were Firmicutes or unclassified species and there was a lack of Fibrobacteres, but for the first time we observed a high number of Bacteroidetes in rabbit samples. This work re-iterates high levels of Firmicutes and unclassified species are present in the rabbit gut, together with low number of Fibrobacteres. This suggests that in the rabbit gut, organisms other than the Fibrobacteres must be responsible for fibre digestion. However observation of high numbers of Bacteroidetes suggests that this phylum may indeed have a role to play in digestion in the rabbit gut.

Parasitic helminths secrete extracellular vesicles (EVs) which have potent immunomodulatory effects. Whilst the cargo of EVs has been characterised for many species, we know little about the mechanisms that govern their biogenesis and release. Using antibodies raised against a panel of Fasciola hepatica EV (FhEV) marker proteins, we have identified multiple sites of EV production in the parasite. Discrete immunofluorescence patterns were observed within the gastrodermal cells and tegumental syncytium for different marker proteins whilst the protonephridial (excretory) system and parenchymal-type 2 cells were identified as additional sites of production (or transit) of FhEVs. Ligation was used to mechanically block the oral sucker, excretory pore, or both, to determine the effect on FhEV release from live adult flukes in vitro. This revealed that FhEVs are predominately derived from the gut, whilst the tegument releases EVs to a lesser extent. The data also suggest that the protonephridial system contributes to the small (120K) EV sub-population. Sphingomyelinase (SMase) activity is a key driver of EV biogenesis in mammalian cells and we have previously identified SMases in FhEVs by mass spectrometry. SMase activity associated with isolated FhEVs was susceptible to the chemical inhibitor GW4869 and treatment of adult flukes with GW4869 led to a significant reduction in 120K EV release in vitro suggesting that a ceramidedependent mechanism could drive 120K EV formation. In contrast, the release of the larger 15K EVs was only moderately impacted, indicating that they form independently of SMase activity.Ultrastructural observation of GW4869-treated F. hepatica tissue showed severe disruption to the parenchyma and vacuolation of the tegument, gastrodermal cells and epithelial lining of the excretory ducts. This work establishes that targeted disruption of EV biogenesis and release in helminths is possible and provides proof-of-concept for future studies investigating EV secretion as a target for parasite control.

For ruminants, grazing and ruminating activities are essential in nutrient capture and ultimately animal performance however these activities can demand significant time and energy. This study evaluated the effect of three different pasture allocation frequencies (PAF’s; 12, 24 and 36 h) on the feeding behaviour of grazing dairy cows. Eighty-seven spring calving dairy cows were divided into three treatments. Animals were rotationally grazed with fixed paddock sizes of 0.14 ha, 0.28 ha and 0.42 ha paddocks for the 12 h, 24 h and 36 h treatments, respectively. Animals (14 per treatment) were fitted with behaviour halters that monitored feeding activity. Diurnal feeding patterns were evident for all animals irrespective of PAF, concentrating the majority of grazing during daytime (90%) and ruminating activity during night (73%). Treatment significantly affected feeding behavior patterns. Peak grazing activity coincided with fresh pasture allocation in the 12 h and 24 h treatments. In the 36 h treatment, grazing was more evenly distributed over each 24 h period with peak grazing activity witnessed daily between 17:00 and 19:00 regardless of fresh pasture allocation, suggesting lack of anticipation of fresh feed delivery. In the 12 h treatment primiparous animals exhibited greater grazing and ruminating activity relative to multiparous animals in the 12 h treatment highlighting the impact of competition for resources within each feed on lower dominance animals.