Overview of Common Types of Parasite Life Cycles

Overview of Common Types of Parasite Life Cycles, Host Specificity and Transmission Strategies

Class Trematoda • Digenetic and aspidogastrean flukes: all parasitic. • Body covered by tegument. • Most have complicated life cycles with 2 -3 or 4 hosts (alternation of generations)

Aspidogastrean flukes

Life Cycle

Life Cycle • First Intermediate Host – Mollusk-snail (One Exception)

Life Cycle • First Intermediate Host – Mollusk-snail • Second Intermediate Host (wide range of animals, including mollusks, arthropods, and vertebrates!

Life Cycle • First Intermediate Host – Mollusk-snail • Second Intermediate Host (wide range of animals, including mollusks, arthropods, and vertebrates! • Definitive Host (in most cases vertebrates) • Reservoir hosts can be both an intermediate host and/or definitive host!

Life Cycle Egg Miracidium Adult Metacercaria Sporocyst Cercaria Redia

Polyembryony Egg Miracidium Adult Metacercaria Sporocyst Cercaria Redia

Multiple Sporocyst/Redia Generations Egg Miracidium Adult Metacercaria Sporocyst Daughter Sporocyst Cercaria Daughter Redia

Egg Miracidium Sporocyst Redia Redia Redia Redia Redia Redia Redia Redia Cercaria Redia Cercaria Cercaria Cercaria Cercaria Cercaria Cercaria Cercaria Cercaria Many Metacercaria Many Adults

Life Cycles • Basic Pathway • Lots of variation (Development, Number of Hosts etc)