Eating raw seafood carries some measure of risk. Parasites such as worms often infect fish and other types of seafood including clams. When people consume infected seafood without properly cooking it, the parasites inside the seafood will transfer to the human being. Worms may infect clams by penetrating the tissue of the clams and living there as parasites. Carnivorous worms usually attach themselves to the clams as they consume them.
Roundworms or nematodes are cylindrical worms that infest seafood like mollusks, including clams. When infested hosts pass their feces in the waters, the eggs of the worms will hatch and develop into larvae. The larvae will infect crustaceans and small invertebrates, such as clams and shellfish, or larger invertebrates like squid. They infect people who eat undercooked or raw infested clams. Roundworms cause anisakiasis, a condition that is characterized by nausea and abdominal pain. Roundworm larvae cannot survive for long in human hosts. Usually, they die off after a week or two. However, in severe cases, the nematodes may have to be surgically removed to provide relief for the infected person.
Trematodes are also known as flukes. They affect a wide variety of hosts, including mollusks such as clams, oysters, mussels, scallops and cockles. Infestation of clams by trematodes leads to poor growth, weakness and death. When people eat uncooked clams, the trematodes in the infected clams will reproduce in their digestive tracts. When infected waste is discharged into bodies of water, the trematode's eggs inside the waste will hatch into larvae and penetrate the tissue of their primary hosts -- water snails. The trematodes develop inside the body of the snails, after which they will be discharged into the water. At this stage, they will penetrate the tissue of their second host, which could be clams, or any other animal that happens to be around.
Ribbon worms look for openings into the body cavity of clams. This is usually through the opening at the foot of the clam. Once inside the body cavity, ribbon worms inject a paralyzing toxin into the clams. The toxin paralyzes the clams, allowing the ribbon worm to secrete part of its digestive enzymes on its prey and suck up the victim's juices. Ribbon worms attach themselves to clams until they completely digest the clam, leaving empty shells. They also deliver painful bites to people trying to dig up clams.
Bloodworms burrow beneath clams and attach themselves to the clam, using their large proboscis. The proboscis has four poisonous jaws with which they kill their prey. The jaws also deliver painful bites to those trying to dig up the clams. Bloodworms have a creamy pink color, and female worms can produce up to 10 million eggs, which quickly develop into larvae.
- Alaska Department of Fish and Game: Trematode Metacercarie and Sporocycts
- Maine Department of Marine Resources: Soft-Shell Clams
- Skylark Medical Clinic: A la Carte - Other Food Born Diseases (A-Z)
- Baby Center: Is It Safe to Eat Seafood During Pregnancy?
- Wild Singapore: Ribbon worms
- AMSCO School Publications: Marine Worms
- Journal of Invertebrate Pathology: Infestation of the Clam Chione fluctifraga by the Burrowing Worm