Parasitology Lab Practical Study Guide –
Parasite Identification, Life Cycles,
Morphology & Diagnostic Techniques
(Complete Review 2026)
Parasitology Lab Practical 2
Platyhelminthes (flatworms)
1. trematodes (flukes)
2. cestodes (tapeworms)
Digenetic Trematodes
most species have 3 hosts
1. definitive host - contains the adult trematode
2. 1st intermediate host = a snail (contains larvae)
3. 2nd intermediate host - contains metacercariae
developmental stages of most trematodes that infect humans:
1. adult trematode (found in the definitive host, a human perhaps)
2. eggs that contain a miracidium larva; miracidum transforms to a
3. sporocyst larva; sporocyst transforms to a
4. redia larva; rediae transform to a
5. cercaria larva; cercariae transform to a
6. metacercaria larva; the meatcercaria is often ingested by a human & transforms to a
7. juvenile; the juvenile develops into an
Adult - cycle completed!
Miracidia. This is the larval stage that exits a trematode egg. Miracidia will find
and penetrate a snail and then form the next larval stage. Miracidia are ciliated
(arrow).
Miracidium; note cilia.
Sporocyst (arrow). This is the first larval stage that forms in a snail. Within the
sporocyst is the next larval stage.
Sporocysts of two different species of trematode.
Rediae. This is the larval stage that forms from sporocysts in a "classical" life
cycle. These have a muscular pharynx and are structurally more complex than
sporocysts.
Cercariae. This larval stage develops from rediae in a classical life cycle. This
larval stage leaves the snail and seeks the next host.
Cercariae.
top photo: light micrograph
bottom: scanning electron micrograph
Cercariae
Rediae and cercariae (white structures) emerging from a crushed snail
,Metacercariae. Once the cercariae have penetrated the next host, the cercarial tail
will fall off and a metacercaria will form. It is a resting stage and a wall will form
around it. The next host must eat the metacercaria for the life cycle to continue.
The order of the larval stages of trematodes is: miracidium, sporocyst, redia,
cercaria, metacercaria. Identify each below.
Egg of Fasciola hepatica. These eggs are the largest of the trematodes that can
infect humans and are nearly identical to eggs of Fasciolopsis buski.
Egg of Fasciola hepatica
Fasciola hepatica
"sheep liver fluke'
worldwide
zoonosis
fascioliasis
Stained Fasciola hepatica adult with labeled structures.
Adult Fasciola hepatica (yellow = uterus with eggs; black arrow = digestive cecae;
see lab book for more structures.)
Locate where the adult Fasciola would be located (feeding and mating).
Living adult Fasciola hepatica.
Fasciola adults seen at necropsy.
Fasciola hepatica adults removed from a cow.
Section of liver with an adult Fasciola hepatica (arrow.
Sheep liver that is infected with Fasciola hepatica. Note the thickened, calcified
bile ducts which contained the adult worms. This condition is sometimes called
"pipestem fibrosis".
Various animal livers showing pathology due to fascioliasis.
Fasciola hepatica (arrow) viewed by endoscopy in a human patient.
47 year old female with 2 weeks of moderate constant right upper quadrant pain.
No fever or systemic symptoms. Referred because of a dilated common bile duct
noted on ultrasound. 4 years ago she had a cholecystectomy for what was
diagnosed as symptomatic gall bladder disease. Exact operative findings from
that time were not available. Epidemiology: Housewife from Abancay, a town in a
rural area high in the Andes. Typical diet for the area with large amounts of
vegetables such as potatoes, corn, and green salads with very little meat or fish.
Physical Examination: Afebrile. Tender abdomen predominantly in the epigastric
area and right upper quadrant, but without peritoneal signs. Normal rectal exam.
2nd Intermediate Host for Fasciola hepatica - Watercress
Watercress is grown in the US and is popular in salads. Any plant that is grown
in/near water would be a suitable host for F. hepatica.
infected plants metacercariae encysted on plants
Clonorchis sinensis
Clonorchis sinensis life cycle
Clonorchis sinensis adult. Blue arrow=uterus, black arrow=vitellaria (=vitelline
gland), red arrow=testes; yellow=seminal receptacle; locate the digestive cecae.
Living adult Clonorchis sinensis. What structure is orange?
Uterus??
Clonorchis sinensis - intermediate hosts
, Clonorchis sinensis eggs
smallest trematode eggs in humans
Clonorchis sinensis eggs
Clonorchis sinensis eggs
note operculum and knob (arrow) at abopercular end
Cyprinid fish, the "2nd intermediate host" for C. sinensis. These fish contain the
metacercariae.
Fish pond in SE Asia where grass carp are cultivated for food. These people are
fertilizing the pond with human feces. It is likely that these feces contain eggs of
C. sinensis. Thus, the 1st intermediate host (snail), 2nd intermediate host (fish)
and definitive host (human/mammal) all live in close proximity.
Area of clonorchiasis (photo from text). Present are: fish pond, restaurant that
serves the fish, outhouse built over the pond.
Numerous Clonorchis sinensis adults removed from a patient.
Paragonimus westermani life cycle
Paragonimus westermani geography
A freshwater crab, the second intermediate host for Paragonimus westermanni,
from SE Asia. It contains metacercariae.
crayfish - 2nd intermediate host for Paragonimus
Second intermediate host and the metacercaria that it contains.
Living Paragonimus westermanni adults from lung. These are often described as
lemon-shaped.
Paragonimus westermanni adult from human lung. The dark mass is the uterus.
How are humans infected? Locate other structures listed in your lab manual.
Histology of P. westermanni adults in lung. The lungs eventually become fibrotic
as the host attempts to encapsulate the adults.
Paragonimus westermanni egg from human sputum or feces. Note operculum at
broad end. These eggs are slightly asymmetrical.
Paragonimus westermani egg
Paragonimus westermanni egg. The operculum is open.
Below is a reservoir for Paragonimus westermanni - a "palm civet" in SE Asia.
Many mammals can serve as reserviors.
X-ray of lung that contains adult P. westermanni. Arrows indicate lesions. The
clinical picture is often confused with active, pulmonary tuberculosis.
A 27-year-old woman was admitted to a local hospital with productive cough and
blood-tinged sputum. Chest X-ray showed multiple nodules and she received
anti-tuberculosis chemotherapy for 2 months. A follow-up chest X-ray taken 2
months later revealed an increased size of the nodules, and the patient was
referred to our hospital.
A chest X-ray showed multiple mass-like opacities in the right lung (Fig. 1A).
Chest CT revealed multiple nodules with adjacent areas of ground-glass opacity
(GGO), which corresponded to hemorrhagic infarcts as in a case of hemorrhagic
metastasis or other benign conditions (Fig. 1B).
Sputum sample contained Paragonimus eggs
Dog lung infected with numerous Paragonimus adults - note nodules.
Paragonimus adults in lung; histology of infection.
Parasite Identification, Life Cycles,
Morphology & Diagnostic Techniques
(Complete Review 2026)
Parasitology Lab Practical 2
Platyhelminthes (flatworms)
1. trematodes (flukes)
2. cestodes (tapeworms)
Digenetic Trematodes
most species have 3 hosts
1. definitive host - contains the adult trematode
2. 1st intermediate host = a snail (contains larvae)
3. 2nd intermediate host - contains metacercariae
developmental stages of most trematodes that infect humans:
1. adult trematode (found in the definitive host, a human perhaps)
2. eggs that contain a miracidium larva; miracidum transforms to a
3. sporocyst larva; sporocyst transforms to a
4. redia larva; rediae transform to a
5. cercaria larva; cercariae transform to a
6. metacercaria larva; the meatcercaria is often ingested by a human & transforms to a
7. juvenile; the juvenile develops into an
Adult - cycle completed!
Miracidia. This is the larval stage that exits a trematode egg. Miracidia will find
and penetrate a snail and then form the next larval stage. Miracidia are ciliated
(arrow).
Miracidium; note cilia.
Sporocyst (arrow). This is the first larval stage that forms in a snail. Within the
sporocyst is the next larval stage.
Sporocysts of two different species of trematode.
Rediae. This is the larval stage that forms from sporocysts in a "classical" life
cycle. These have a muscular pharynx and are structurally more complex than
sporocysts.
Cercariae. This larval stage develops from rediae in a classical life cycle. This
larval stage leaves the snail and seeks the next host.
Cercariae.
top photo: light micrograph
bottom: scanning electron micrograph
Cercariae
Rediae and cercariae (white structures) emerging from a crushed snail
,Metacercariae. Once the cercariae have penetrated the next host, the cercarial tail
will fall off and a metacercaria will form. It is a resting stage and a wall will form
around it. The next host must eat the metacercaria for the life cycle to continue.
The order of the larval stages of trematodes is: miracidium, sporocyst, redia,
cercaria, metacercaria. Identify each below.
Egg of Fasciola hepatica. These eggs are the largest of the trematodes that can
infect humans and are nearly identical to eggs of Fasciolopsis buski.
Egg of Fasciola hepatica
Fasciola hepatica
"sheep liver fluke'
worldwide
zoonosis
fascioliasis
Stained Fasciola hepatica adult with labeled structures.
Adult Fasciola hepatica (yellow = uterus with eggs; black arrow = digestive cecae;
see lab book for more structures.)
Locate where the adult Fasciola would be located (feeding and mating).
Living adult Fasciola hepatica.
Fasciola adults seen at necropsy.
Fasciola hepatica adults removed from a cow.
Section of liver with an adult Fasciola hepatica (arrow.
Sheep liver that is infected with Fasciola hepatica. Note the thickened, calcified
bile ducts which contained the adult worms. This condition is sometimes called
"pipestem fibrosis".
Various animal livers showing pathology due to fascioliasis.
Fasciola hepatica (arrow) viewed by endoscopy in a human patient.
47 year old female with 2 weeks of moderate constant right upper quadrant pain.
No fever or systemic symptoms. Referred because of a dilated common bile duct
noted on ultrasound. 4 years ago she had a cholecystectomy for what was
diagnosed as symptomatic gall bladder disease. Exact operative findings from
that time were not available. Epidemiology: Housewife from Abancay, a town in a
rural area high in the Andes. Typical diet for the area with large amounts of
vegetables such as potatoes, corn, and green salads with very little meat or fish.
Physical Examination: Afebrile. Tender abdomen predominantly in the epigastric
area and right upper quadrant, but without peritoneal signs. Normal rectal exam.
2nd Intermediate Host for Fasciola hepatica - Watercress
Watercress is grown in the US and is popular in salads. Any plant that is grown
in/near water would be a suitable host for F. hepatica.
infected plants metacercariae encysted on plants
Clonorchis sinensis
Clonorchis sinensis life cycle
Clonorchis sinensis adult. Blue arrow=uterus, black arrow=vitellaria (=vitelline
gland), red arrow=testes; yellow=seminal receptacle; locate the digestive cecae.
Living adult Clonorchis sinensis. What structure is orange?
Uterus??
Clonorchis sinensis - intermediate hosts
, Clonorchis sinensis eggs
smallest trematode eggs in humans
Clonorchis sinensis eggs
Clonorchis sinensis eggs
note operculum and knob (arrow) at abopercular end
Cyprinid fish, the "2nd intermediate host" for C. sinensis. These fish contain the
metacercariae.
Fish pond in SE Asia where grass carp are cultivated for food. These people are
fertilizing the pond with human feces. It is likely that these feces contain eggs of
C. sinensis. Thus, the 1st intermediate host (snail), 2nd intermediate host (fish)
and definitive host (human/mammal) all live in close proximity.
Area of clonorchiasis (photo from text). Present are: fish pond, restaurant that
serves the fish, outhouse built over the pond.
Numerous Clonorchis sinensis adults removed from a patient.
Paragonimus westermani life cycle
Paragonimus westermani geography
A freshwater crab, the second intermediate host for Paragonimus westermanni,
from SE Asia. It contains metacercariae.
crayfish - 2nd intermediate host for Paragonimus
Second intermediate host and the metacercaria that it contains.
Living Paragonimus westermanni adults from lung. These are often described as
lemon-shaped.
Paragonimus westermanni adult from human lung. The dark mass is the uterus.
How are humans infected? Locate other structures listed in your lab manual.
Histology of P. westermanni adults in lung. The lungs eventually become fibrotic
as the host attempts to encapsulate the adults.
Paragonimus westermanni egg from human sputum or feces. Note operculum at
broad end. These eggs are slightly asymmetrical.
Paragonimus westermani egg
Paragonimus westermanni egg. The operculum is open.
Below is a reservoir for Paragonimus westermanni - a "palm civet" in SE Asia.
Many mammals can serve as reserviors.
X-ray of lung that contains adult P. westermanni. Arrows indicate lesions. The
clinical picture is often confused with active, pulmonary tuberculosis.
A 27-year-old woman was admitted to a local hospital with productive cough and
blood-tinged sputum. Chest X-ray showed multiple nodules and she received
anti-tuberculosis chemotherapy for 2 months. A follow-up chest X-ray taken 2
months later revealed an increased size of the nodules, and the patient was
referred to our hospital.
A chest X-ray showed multiple mass-like opacities in the right lung (Fig. 1A).
Chest CT revealed multiple nodules with adjacent areas of ground-glass opacity
(GGO), which corresponded to hemorrhagic infarcts as in a case of hemorrhagic
metastasis or other benign conditions (Fig. 1B).
Sputum sample contained Paragonimus eggs
Dog lung infected with numerous Paragonimus adults - note nodules.
Paragonimus adults in lung; histology of infection.
