Blood Clams
Cultured from South Africa to northern Japan, blood clams live in low-oxygen environments and filter up to 40 liters of seawater per day, making them more likely to absorb harmful bacteria and viruses including hepatitis, typhoid, and dysentery.
The common Chinese preparation of boiling the clams very briefly leaves these viruses intact. Unsurprisingly, they were banned in Shanghai following a hepatitis A outbreak in 1988.