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This project provides a definitive statement on the susceptibility of ecologically and economically important European crustacean species to White Spot Syndrome Virus (WSSV). Exposure trials revealed universal susceptibility to WSSV infection in seven hosts, and that relative susceptibility varies significantly between species. To determine whether WSSV infection would remain in the tissues of crabs as persistent infections (or whether these crabs would clear the viral infection from their systems over time) crabs were fed with WSSV-infected tissues and then observed in tanks for 3 months. Results suggested that the carcasses of infected (but not diseased) shore and edible crab crabs appear to pose a limited risk of transmission to susceptible hosts within the 3 month timeframe of the study. The European shore crab (Carcinus maenas) was shown to display a lower suscept ibility to White Spot Syndrome Virus (WSSV) when compared to other European decapod species. Despite showing signs of infection with WSSV, the shore crab appeared resistant to the development of disease and was highlighted as a possible asymptomatic carrier of the virus. Carcinus maenas individuals which had been injected with WSSV and then exposed to varying temperature stress conditions were compared. This suggested that crabs could be divided into two groups (high and low responders) according to differences in pathogenesis and viral replication. The response was not dependent on the presence or absence of an external stressor but was more likely an inherent capacity within individual crabs. A small scale survey of supermarket commodity shrimp confirmed the presence of WSSV-contaminated products within shrimp imported for human consumpt ion, demonstrating that frozen commodity shrimp is a route of entry for WSSV into Europe. Experimental trials showed that this virus is viable and that the commodity products were infective and could passage the infection to naive crustaceans that are known to be susceptible to the virus, highlighting this practice needs to be considered and controlled in risk assessments . Analysis of WSSV Variable Nucleotide Tandem Repeats (VNTR) within ORF 94 following passage through different hosts revealed subtle differences in WSSV VNTR types present in crab and crayfish tissues suggesting that the host may influence which viral type propagates during infections. These studies also identified and described two novel virus infections. The viral infections mimic the appearance of WSSV and highlight the importance of being able to fully characterise virus infections when they are first identified.