The European flat oyster (Ostrea edulis) was once widespread in the North Sea. However, overfishing, habitat destruction and infectious diseases pushed the species to the brink of extinction in some regions nearly one hundred years ago. In particular, infections with the pathogen Bonamia ostreae have caused repeated major losses since the 1970s. The parasite infects the oysters' immune cells and initially causes no symptoms, but after several months the infection can become systemic—a condition known as bonamiosis—ultimately leading to the oyster's death.