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