What is the typical route of human infection with Diphyllobothrium latum?

• A. Ingesting raw or undercooked freshwater fish containing larval plerocercoids
• B. Ingesting contaminated water with eggs
• C. Bites from infected insects
• D. Skin penetration by cercariae

Answer: (A)

Humans acquire Diphyllobothrium latum infection by eating raw or undercooked freshwater fish that harbor the plerocercoid larva. The parasite’s life cycle involves eggs shed in feces reaching freshwater, where they develop through intermediate hosts and end up as plerocercoids in fish; when people eat that infected fish, the plerocercoids are released in the small intestine and mature into adult tapeworms. This route explains why dishes featuring raw fish are a risk and why proper cooking or freezing of fish prevents infection. Other routes, such as ingestion of contaminated water with eggs, insect bites, or skin penetration by cercariae, do not apply to this tapeworm’s transmission.