Parasitology. Trematodes

Trematodes. Infective in Metacercarial Stage. Infective in Cercarial Stage

General Morphology

hermaphroditic or separate sexes depending on species

flatworms

acetabula - suckers

General Characteristics

all exotic to U.S.

digenetic

intermediate host - snails/mollusks

complicated life cycles with multiple stages/hosts

Digenetic

sexual reproductive cycle in vertebrates (definitive host)

asexual reproductive cycle in invertebrates (intermediate host)

cycles alternate

Acetabula

cup shaped suckers - oral and ventral

General Life Cycle Stages

egg

miracidium

1st generation sporocyst - Mother sporocyst

2nd generation sporocyst. - Daughter sporocyst or redia

cercaria or metacercaria → infective stage

adult worm

Egg

variety of size and shape - depends on species

operculating (infective in metacercarial)

“cutting tool“ spine → lots of pathology (shistosomes)

1st generation sporocyst - Mother sporocyst

asexual stage in snail host

elongated sack with offspring → released via birth pore

produce multiple 2nd gen sporocyst - daughter sporocyst or redia depending on species

2nd generation sporocyst - Daughter sporocyst or redia

part of asexual reproduction in snail host

produces cercaria

daughter sporocyst or redia depending on species

Cercaria

free swimming stage

non-feeding

infective for definitive host

metacercaria or cercaria

Difference between cercaria and metacercaria

cercaria - twin, forked tail; direct infection through skin

metacercaria - single tail; encysts on plants/animal; indirect infection via ingestion

Miracidium

non-feeding

infective for intermediate host - penetrate soft tissue

cilia for swimming

live 24 hours

Difference between redia and daughter sporocyst

daughter sporocyst - no internal organs, only sack

redia - oral cavity, organ cavity

Characteristics of Trematodes Infective in Metacercarial Stage

digenetic

hermaphroditic

operculated eggs

cercaria are straight tailed

infective stage: encysted metacercarias

Fasciolopsis buski Life Cycle

eggs in stool

embryonated eggs in water

miracidia hatch

penetrate snail

sporocyst → radiae → cercariae (in snail)

free-swimming cercariae

metacercariae on water plant

ingestion of contaminated water plant (by human/pig)

exyst in duodenum

adults in small intestine

Fasciolopsis buski Epidemiology

Asia

pig = reservoir host

night soil is a component for transmission

Fasciolopsis buski Pathology

traumatic damage → irritation, ulceration, hemorrhage

intestinal obstruction - small intestine (heavy infection)

toxic metabolites → diarrhea, undigested food, anorexia, green/yellow stool

Fasciolopsis buski Diagnosis

eggs in stool

Fasciolopsis buski Prevention

treat sewage

age night soil

kill snails

boil water plants

Fasciolopsis buski Hosts

intermediate - snail

definitive - human

reservoir - pig

Fasciolopsis buski (LC pic)

Fasciola spp. Life Cycle

unembryonated eggs in feces

embryonated eggs in water

miracidia hatch

penetrate snail

sporocyst → rediae → cercariae (in snail)

free swimming cercariae

metacercariae on aquatic vegetation

ingestion of contaminated vegetation (by ruminants/humans)

exyst in duodenum

penetrate intestinal wall

migrate to liver → bile duct

adults in hepatic biliary duct

Fasciola spp. Epidemiology

eating watercress

more common in animals

brought to the U.S. by infected people

Fasciola spp. Pathology

scar tissue from migration

pipestem fibrosis

cavities with granulation tissue, fibrous tissue, calcification

development of cirrhosis

Fasciola spp. Diagnosis

eggs in stool

duodenal aspirate or bile duct aspirate

ultrasound - sonogram of liver/bile duct/gall bladder

CT/MRI of liver

Fasciola hepatica

Common (sheep) Liver Fluke

Fasciola gigantica

Giant Liver Fluke

Fasciolopsis buski

Giant Intestinal Fluke

Comparison of Fasciola hepatica and Fasciola gigantica

hepatica - prominent shoulders, smaller

gigantica - narrower shoulders, larger

Fasciola spp. (LC pic)

Fasciola spp. Hosts

intermediate - snail

definitive - ruminants (cattle, sheep)

accidental - humans

Fasciola spp. Prevention

cook water-grown vegetables

wash water-grown vegetables (6% vinegar or potassium permanganate)

avoid sewage contamination of growing areas

treatment of animals

use of molluscicides

Clonorchis sinensis Life Cycle

embryonated eggs in feces

eggs ingested by snail

miracidia → sporocyst → redial → cercariae

free-swimming cercaria encyst on the skin/flesh of fish

human ingests contaminated fish

exist in dudodenum

adults in biliary duct

Clonorchis sinensis Epidemiology

reservoir host: cats, dogs

night soil helps distribution

eating raw/undercooked fish

East Asia (Japan, Korea, China, Taiwan, Vietnam)

Clonorchis sinensis Pathology

low exposure → little to no pathology

high worm burden → bile duct & liver damage

irritation, inflammation , cell proliferation, fibrosis, blockage, neoplasia (bile duct)

travel up tributaries to feed on liver → damage & cirrhosis

risk of bile duct cancer

Clonorchis senensis Diagnosis

eggs in feces

Clonorchis senensis Prevention

treat/age night soil

cook fish

kill snails

Clonorchis sinensis

Liver Fluke

Clonorchis sinensis Hosts

intermediate - snails, fresh water fish

definitive - humans

reservoir - cats, dogs

Clonorchis sinensis (LC pic)

Paragonimus westermani Life Cycle

unembryonated eggs → embryonated eggs

miracidia hatch and penetrate snails

sporocyst → rediae → cercariae (in snail)

cercariae invade crustacean

metacercariae in crustacean

human ingests crustacean

exyst in duocedum

travel through diaphragm to lungs

adults in cystic cavities in lungs

eggs in sputum or in stool (if swallowed)

Paragonimus westermani Epidemiology

reservoir host: cats, dogs, pigs

East/Southeast Asia - endemic

U.S. - mostly due to people arriving from endemic areas

possible problem in U.S. - Louisiana, may be endemic

Paragonimus westermani Pathology

mechanical damage from migration

encystment in lung (fibrous capsule, tubercle-like abcess)

cough and chest pain

encystment in other organs

prognosis depends on worm burden

Paragonimus westermani Diagnosis

eggs in sputum

eggs in feces

X-ray and imaging (CT)

Paragonimus westermani Prevention

treat sewage

age night soil

cook or freeze crustaceans

prohibit spitting → no eggs in water

Paragonimus westermani (LC pic)

Paragonimus westermani Hosts

intermediate - snail, crustacean (crabs, crayfish)

definitive - human

reservoir - cat, dog, pig

Characteristics of Trematodes Infective in Cercarial stage

separate sexes

eggs with spines - “cutting tools“

most pathology caused by eggs

cercaria have forked tails → good swimmers

infective stage: cercaria penetrating skin