more susceptible to Dermo or MSX infections than are the C. gigas species of oyster. Pathogens of O. edulis oysters include Marteilia refringens and Bonamia ostreae. In the north Atlantic Ocean, oyster crabs may live in an endosymbiotic commensal relationship within a host oyster. Since oyster crabs are considered a food delicacy they may not be removed from young farmed oysters, as they can themselves be harvested for sale. Dermo disease is caused by a protozoan parasite that infects the oyster's blood cells: Perkinsus marinus. It is spread when infective stages are released into the water column from an infected oyster and siphoned into a new host. It is most common in water above 77 °F. MSX stands for “Multinucleated Sphere Unknown” and is lethal to C. virginica. It is a single-celled protozoan with an unknown method of transmission between oysters. It does not appear to transfer from oyster-to-oyster like Dermo does. After an outbreak in 1997, a strain of MSX-resistant oysters were developed. MSX can be suppressed by low temperatures and low salinities, but once infected, oysters will die within a month. MSX and Dermo are both considered to be non-harmful to humans. Vibrio, however, is a disease that is carried by oysters and other shellfish and can make people sick, but is not harmful to the oyster itself. Vibrio can only be passed from oysters to humans if they are consumed raw. Vibrio is more common in warmer waters, and all commercial shellfish must be refrigerated before being served in an attempt to kill the vibrio bacterium. Polydorid polychaetes are known as pests of cultured oysters. See also Gathering seafood by hand Oyster pirate Oystering machinery References Further reading External links The History of Oyster Culture in BC. (1985). Malaspina College. The Oystermen Documentary produced by Oregon Public Broadcasting Oysters Aquaculture