Transcript PRINCIPLES AND DEFINITIONS (Chap. 2 & 3)

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 23 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
Redia
Egg
Miracidium
Sporocyst
Sporocyst
Redia Redia Redia
Sporocyst
Redia Redia Redia
Sporocyst
Redia Redia Redia
Redia Redia Redia
Redia Redia Redia
Redia Redia Redia
Redia Redia Redia
Redia Redia Redia
Redia Redia Redia
Redia Redia Redia
Redia Redia Cercaria
Redia
Redia Redia Redia
Cercaria Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria Cercaria
Cercaria
Cercaria Cercaria Cercaria Cercaria
Cercaria
Cercaria
Cercaria Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
CercariaCercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria
Cercaria CercariaCercaria
Cercaria
Cercaria Cercaria
Many Metacercaria
Many Adults
Life Cycles
• Basic Pathway
• Lots of variation (Development, Number
of Hosts etc)