Platyhelminths as Human
Parasites
Images from the CDC
Trematode Parasites
• Clonorchis sinensis
• Fasciola hepatica
• Schistosoma spp.
– mansoni
– japonicum
– Haematobium
• Paragonimus westermani
• Dicrocoelium dendriticum
Clonorchis sinensis
• Chinese Liver Fluke
• 20 Million Infected
People
• Infection by eating raw
or udercooked fish
(pickled fish)
• Flukes live in bile ducts
• Symptoms
– Pain in upper rt.
Quadrant
– Hepatosplenomegaly
– Gall Stones
– Obstructive Jaundice
– Bile Duct Cancer
Clonorchis sinensis
Fasciola hepatica
• Sheep Liver Fluke
• Human infection
from eating wild
aquatic plants
• Symptoms
–
–
–
–
–
Hepatosplenomegaly
Anemia
Jaundice
Abdominal Pain
Fatty Food
Intolerance
Schistosoma spp.
• Dioecious
• Large males with
split bodies forming
a longitudinal
groove
• Females housed in
groove of male
• Adults may live for
10-30 years
Schistosoma spp.
• Schistosoma mansoni
– Egg with large
subterminal spine
– Adults in veins of large
intestine
• Schistosoma japonicum
– Egg with diminutive
subterminal spine
– Adults in veins of small
intestine
• Schistosoma
haematobium
– Egg with terminal spine
– Adults in veins of urinary
bladder
Schistosomiasis
Intermediate Hosts of
Schistosomes
• Schistosoma mansoni
– Africa, S. America, West
Indies
– Int. Host - Biomphalaria
• Schistosoma japonicum
– Asia
– Int. Host - Oncomelania
• Schistosoma
haematobium
– Africa
– Int. Host - Bulinus
Schistosome Cercaria
• Cercariae penetrate
skin of definitive host
• Schistosomes that
normally parasitize
birds may produce the
rash known as
swimmer’s itch. The
rash is the result of an
immune response to the
cercariae.
Schistosomiasis
• Blood Flukes
• 200 Million people
infected in Africa
and Asia
• Symptoms
– Ascites
– Symmer’s Fibrosis
– Death via
hemorrhage
Control of Schistosomes
• Proper disposal of body
waste
• Avoid contact with
contaminated water
• Vaccine?
• Biological Control?
• Aswan High Dam
– Electricity
– Agriculture
– Schistosomiasis
Paragonimus westermani
• Lung Fluke
• Widely Distributed
– >10 million people
infected in China
• Infection by eating raw
or undercooked
crustaceans
• Symptoms
– Chronic Cough
– Purulent, blood-streaked
sputum
– Jacksonian Epilepsy,
meningitis (cerebral
infection)
– Death (pericardial
infection)
Dicrocoelium dendriticum
• Liver fluke of
livestock
• Humans are
accidental hosts
• Mind-controlling
effect on ants
Cestode Parasites
•
•
•
•
Taenia saginata
Taenia solium
Diphyllobothrium latum
Echinococcus spp.
Taenia saginata
• Beef Tapeworm
• Cows are
intermediate host
• Scolex without
hooks
• Motile proglottids
Taenia solium
• Pork Tapeworm
• Pigs are
intermediate host
• Scolex with hooks
Taeniasis
Diphyllobothrium latum
• Broad Fish
Tapeworm
• Single worms up to
20 meters
• Most severe adult
tapeworm disease
– Vitamin B12
absorption by worms
leads to anemia
Diphyllobothriasis
Cysticercosis
• Infection by juvenile
tapeworms
• Symptoms related to
location of cysticerci
– Brain
– Eyes
– Heart
Echinococcus spp.
• Hydatid Disease
• Infection by close
contact with sheep
dogs
• Cysts may grow for
many years
• Surgical removal
after scolicidal flush