Why Can Shellfish Cause Food Poisoning?

Shellfish are very high in protein and low in fat and as such they are very good for humans, but they do carry a risk of food poisoning.  This is because they can be contaminated by protozoa, which are microscopic sea animals, bacteria, viruses and toxic algae.  
Molluscs, such as oysters, muscles and scallops are fliter feeders and gallons of water pass through them every day which means that they can easily accumulate harmful levels of bacteria and viruses if the water is polluted by sewage or toxins.  Crustaceans such as lobsters and prawns are usually not such a high risk because we don't eat the organs which filter food in either of these two types of shellfish.
However, within the European Union, there are now very tight criteria surrounding catching shellfish and the waters where they can be caught, so the risk is low.  If you are generally in good health then the body can usually combat small levels of bacteria, so just enjoy !

Shell fish in general are "Mother Natures" vacuum cleaners! So if the bottom gets churned up a lot then the bacteria count rises!

It's that simple!