Trichuris WAP and CAP proteins: Potential whipworm vaccine candidates?

Trichuris trichiura and T. suis are gastrointestinal dwelling roundworms that infect humans and pigs, respectively. Heavy infections cause gastrointestinal symptoms and impaired growth and development. Vaccination has the potential to reduce the disease burden of whipworm infection; however, there are currently no commercially available vaccines against these parasites and very few against other gastrointestinal-dwelling nematodes of medical and agricultural importance. The naturally occurring mouse whipworm, T. muris, has been used for decades to model human trichuriasis, and the immunogenic potential of the excretory/secretory material (E/S, which can be collected following ex vivo culture of worms) has been studied in the context of vaccine candidate identification. Despite this, researchers are yet to progress an effective vaccine candidate to clinical trials. The T. muris, T. trichiura, and T. suis genomes each encode between 10 and 27 whey acidic protein (WAP) domain-containing proteins and 15 to 34 cysteine-rich secretory protein/antigen 5/pathogenesis related-1 (CAP) family members. WAP and CAP proteins have been postulated to play key roles in host-parasite interactions and may possess immunomodulatory functions. In addition, both protein families have been explored in the context of helminth vaccines. Here, we use phylogenetic and functional analysis to investigate the evolutionary relationship between WAP and CAP proteins encoded by T. muris, T. trichiura, and T. suis. We highlight several WAP and CAP proteins that warrant further study to understand their biological function and as possible vaccine candidates against T. trichiura and/or T. suis, based on the close evolutionary relationship with WAP or CAP proteins identified within T. muris E/S products.

Consistency of Bacterial Communities in a Parasitic Worm: Variation Throughout the Life Cycle and Across Geographic Space.

Microbial communities within metazoans are increasingly linked with development, health and behaviour, possibly functioning as integrated evolutionary units with the animal in which they live. This would require microbial communities to show some consistency both ontogenetically (across life stages) and geographically (among populations). We characterise the bacteriome of the parasitic trematode Philophthalmus attenuatus, which undergoes major life cycle transitions, and test whether its bacteriome remains consistent on developmental and spatial scales. Based on sequencing the prokaryotic 16S SSU rRNA gene, we compared the parasite bacteriome (i) across three life stages (rediae in snails, cercariae exiting snails, adults in birds) in one locality and (ii) among three geographic localities for rediae only. We found that each life stage harbours a bacteriome different from that of its host (except the adult stage) and the external environment. Very few bacterial taxa were shared among life stages, suggesting substantial ontogenetic turnover in bacteriome composition. Rediae from the three different localities also had different bacteriomes, with dissimilarities increasing with geographical distance. However, rediae from different localities nevertheless shared more bacterial taxa than did different life stages from the same locality. Changes in the bacteriome along the parasite's developmental history but some degree of geographical stability within a given life stage point toward non-random, stage-specific acquisition, selection and/or propagation of bacteria.

Parasitological research in the molecular age.

New technological methods, such as rapidly developing molecular approaches, often provide new tools for scientific advances. However, these new tools are often not utilized equally across different research areas, possibly leading to disparities in progress between these areas. Here, we use empirical evidence from the scientific literature to test for potential discrepancies in the use of genetic tools to study parasitic vs non-parasitic organisms across three distinguishable molecular periods, the allozyme, nucleotide and genomics periods. Publications on parasites constitute only a fraction (<5%) of the total research output across all molecular periods and are dominated by medically relevant parasites (especially protists), particularly during the early phase of each period. Our analysis suggests an increasing complexity of topics and research questions being addressed with the development of more sophisticated molecular tools, with the research focus between the periods shifting from predominantly species discovery to broader theory-focused questions. We conclude that both new and older molecular methods offer powerful tools for research on parasites, including their diverse roles in ecosystems and their relevance as human pathogens. While older methods, such as barcoding approaches, will continue to feature in the molecular toolbox of parasitologists for years to come, we encourage parasitologists to be more responsive to new approaches that provide the tools to address broader questions.