EAGER: Viruses of the Protozoan Parasites Perkinsus spp.: Isolation and Characterization

Bigelow Laboratory For Ocean Sciences, East Boothbay ME

Investigators

Abstract

Oysters and clams are often challenged by parasites, including Perkinsus species. Perkinsus spp., causative of Dermo disease, can lead to mass mortalities of farmed and wild bivalve populations and hence have important detrimental ecological and economic consequences. Perkinsus is on the World Organization for Animal Health's list of reportable diseases. Most of the studies aimed to understand and intervene against Dermo have centered in a game of two: parasite and host. However, previous ultrastructural studies have shown the presence of virus-like particles in the nucleus of the parasite. Yet, nothing is known about these viruses' genetics, mechanism of infection, or consequences on Perkinsus ecology. Research on other parasitic protozoa (including some with human hosts) has revealed many interesting biological phenomena that suggest that there is every reason to expect that viruses have a profound effect on the propagation, life style and virulence of Perkinsus spp. Proving viral infection of Perkinsus spp. and understanding the host's functional responses to infections will represent a paradigm shift in our thinking about Perkinsus spp. ecology and virulence toward their bivalve hosts. Furthermore, it will open the door to new approaches for intervention against the disease-causing agent. This project is considered high risk-high payoff since, thus far, compelling evidence of viruses infectious to Perkinsus is based on ultrastructural studies using electron microscopy, but information to assess ease of virus isolation is lacking. This project focuses on isolating and characterizing viruses that infect Perkinsus spp. This is a necessary first step toward understanding the dynamics of viral infection of Perkinsus spp. cells and the effects of viruses on the propagation and virulence of this protozoan parasite. In this study, work will focus on the three Perkinsus spp. (P. marinus, P. chesapeaki, and P. olseni) for which there is previous evidence of viral infection. The investigators will isolate viruses specific to several Perkinsus strains already in culture as well as from new Perkinsus spp. isolates. Effort will be put in establishing cultures from those isolates and to optimize propagation and maintenance of the viruses in the laboratory. They will also conduct growth curve experiments, and investigate the effect of viral infection on Perkinsus physiology and as a potential trigger for cell differentiation. Having well characterized model virus-host systems in culture is essential to investigate the environmental parameters that affect viral replication success and specificity. It will also aid in understanding the mechanisms of virus-host interactions and their ecological and physiological consequences through hypothesis driven experimental manipulation. Overall, this project will help to evaluate the ubiquity of viruses that infect Perkinsus spp. and the roles they play in shaping the life cycle and the virulence of these parasites of bivalves.