Trematodes (Flukes)

• Small, flat, leaf-like worms, flattened dorso-ventrally with no body cavity

• Body mass consists of: mesodermal parenchyma, where internal organs are embedded

• Oral and ventral suckers that help attach to the host

• Infest various organs of the human host

  • e.g. intestinal veins, urinary bladder, liver, lung

• Use freshwater snails as an intermediate host

Classification

Domain: Eukaryote

Kingdom: Animalia

Phylum: Platyhelminthes (flatworms)

Class: Trematodes (flukes)

Hermaphroditic Flukes

Hermaphrodite: organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes

Life cycle beginning: hermaphroditic adult fluke produces eggs in the human (definitive host)

• eggs are excreted into the environment

• first larval stage (miracidium) develops inside the eggs

• the larvae seek out and infect suitable snail species (first intermediate host)

• asexual reproduction occurs in the snail

  • several intermediate development forms can be distinguished (sporocyst, redia) and the final larval stage (cercaria)

• leave the snail and seek out second intermediate host

  • a fish or crustacean

• in the second intermediate host, the cercaria form cysts called metacercaria excysts

• if the infected raw or under-cooked fish or crustacean is eaten by a human, the metacercaria excysts, and the fluke invades tissues (such as the lung or liver) and begins producing eggs

Sexual Flukes (Schistosomes)

• called “blood flukes”

• have separate distinct sexes

• similar life cycle to hermaphroditic flukes

• only one intermediate host (snail)

• acquired by: schistosome cercaria directly penetrating the skin in contaminated rivers and lakes

• adult schistosomes take up residence in various abdominal veins

• in fresh water, the organisms infect snails (in which they multiply)

  • cercaria are released into the fresh water

Trematodes Include

• Hepatic/liver flukes

  • Fasciola hepatica

• Intestinal flukes

  • Fasciolopsis buski

  • Heterophyes heterophyes

• Lung flukes

  • Paragonimus westermani

• Blood flukes

  • Schistosoma haematobium

  • Schistosoma mansoni