New insights into the Manila clam - Perkinsus olseni interaction based on gene expression analysis of clam hemocytes and parasite trophozoites through in vitro challenges

Perkinsus spp. Occurrence in South America: A review

Marine mollusk production is increasing worldwide, and this trend is being evidenced in South American countries, where several species of bivalves are produced, exploited, and traded. This activity brings benefits either for the ecosystem, as it is a less impactful and polluting than other aquaculture practices, and to coastal human communities, as it provides food and income. However, emergence of outbreaks by pathogens is a major concern and can put an entire developing sector at risk. Perkinsosis is a disease caused by Perkinsus spp. protozoans that affect mollusks worldwide. In this review we provide information on Perkinsus spp. among bivalves from South America. Infections by these parasites were only reported to date among coastal Atlantic bivalves of Argentina, Uruguay, and Brazil. The vast majority of cases and studies are reported from Brazil. We comprehensively review those results here. Finally, we suggest some considerations for future investigations that may expand our knowledge of these parasites.

Characterisation of common hypothetical surface peptides between protozoan parasites (Perkinsus olseni) originating from different geographical locations

Perkinsus olseni and P. marinus are classified as notifiable pathogens by the World Organisation for Animal Health and are known to cause perkinsosis in a variety of molluscs globally. Mass mortalities due to these parasites in farms and in the wild have been a recurrent issue. Diagnosis for these protozoans is currently done using Ray's fluid thioglycollate medium method followed by optical microscopy or molecular assays. Both require a high level of skill and are time-consuming. An immunoassay method would make the diagnosis of perkinsosis quicker and cheaper. The present study used mass spectrometry-based proteomics to investigate common hypothetical surface peptides between different geographical isolates of P. olseni, which could be used to develop immunoassays in the future. Two peptides were identified: POLS_08089, which is a 42.7 kDa peptide corresponding to the 60S ribosomal subunit protein L4; and POLS_15916, which is a conserved hypothetical protein of 55.6 kDa. The identification of peptides may allow the development of immunoassays through a more targeted approach.

Search for new biomarkers of tolerance to Perkinsus olseni parasite infection in Ruditapes decussatus clams

The grooved carpet shell (Ruditapes decussatus) is a clam species with high economic and social importance in several European and Mediterranean countries. Production of this species suffered a decline caused by biotic (parasite infection) and abiotic factors (environmental factors, stress, poor management methods and intensive culture of the introduced species Ruditapes philippinarum). The protozoan parasite Perkinsus olseni is also responsible for the decline of production, being nowadays one of the major issues for clam culture. Molecular biomarkers that might represent tolerance of R. decussatus to P. olseni have already been uncovered, shedding light in a possible production improvement by selecting those clams with a strongest immune response. In the present study, new tolerance biomarkers to P. olseni infection in R. decussatus were identified. The haemolymph proteomic profiles of naturally non/low-infected (tolerant) and highly-infected (susceptible) clams by the parasite across several heavy affected areas of Europe were characterized through a shotgun proteomics approach. Also, the mechanisms that might be involved in the responses against the disease in chronic infections were explored. Proteins related to energy restoration and balance, metabolic regulation, energy accumulation, ROS production, lysosomal activity, amino acid synthesis, proteolytic activity, iron regulation, iron withholding, and immune response modulation were significantly regulated in susceptible clams. In the tolerant group, proteins related to phagocytosis regulation, control of cell growth and proliferation, gonadal maturation, regulation of apoptosis, growth modulation, response to oxidative stress, iron regulation, shell development and metabolic regulation were significantly expressed. In summary, the protein expression profile of tolerant individuals suggests that an efficient pathogen elimination mechanism coupled to a better metabolic regulation leads to a tolerance to the parasite infection by limiting the spread through the tissues.