Digenetic Trematodes of Importance

We will study important digenetic trematodes (=flukes) by where they live in the definitive host.

Liver flukes

Lung flukes

Reproductive System Flukes

Intestinal Flukes

Blood Flukes

Liver Flukes3 families of digenetic trematodes inhabit the livers of mammals.

Important species of medical and veterinary importance are found in these families.

 

FAMILY FASCIOLIDAE – Chapter 17, p. 268-272

Large leaf-shaped flukes.

Most are parasites in livers of mammals, but 1 species occurs in small intestine.

 

Fasciola hepatica

First trematode to be described: de Brie (1379) described this parasite as causing “____________________________________”

First trematode in which the life cycle was worked out in 1883 - accomplished simultaneously by a British graduate student A. P. Thomas and eminent German parasitologist Rudolph Leuckart.

Morphology of adult Fasciola hepatica

Large, leaf-shaped fluke, reaching a size of 30 mm long and 13 mm wide.

Characteristics:

- ________________________ at anterior end contains the _________________________________________________________________________________

- body widens at base of oral cone to form “_______________” - identifying character

Morphology of adult Fasciola hepatica

Internal organs are branched

- ________________________ is branched near the uterus

- ________________________ is in middle of body near ovary

- lateral ___________________ are extensive

- _____________________ are tandem and highly branched

- ________________________ are highly branched

Branching of internal organs makes them difficult to identify.

Morphology of adult Fasciola hepatica

acetabulum

Definitive hosts & Distribution of Fasciola hepatica

Adults occur in the bile ducts of the livers of _____________ ___________________________________________________________________________ in southern and western U.S.

 - presence in sheep and cattle is of veterinary importance

- in Wisconsin?

- human cases? 

Life cycle of Fasciola hepatica1. ________________________ inhabit the _________________ of the liver of the definitive host.

2. ________________________ are released into the bile, enter the duodenum, pass through the digestive tract, and are voided in the feces.

- Eggs must be released into an aquatic habitat and will hatch in 14 days.

3. ________________________ hatches from egg, swims about until finding a pond snail (Lymnaea sp.), and penetrates the snail to become a ____________ __________________________.

Life cycle of Fasciola hepatica4. Within the snail, the mother sporocyst produces ____________________________ which produce ____________________________ which produce ________________

-Cercariae are released from the snail 4-7 weeks after miracidial penetration.

5. Cercariae swim about until contacting aquatic vegetation.

They encyst on vegetation as ___________________________.

 - __________________________ is common aquatic plant associated with human infections.

 

Life cycle of Fasciola hepatica6. When the definitive host ingests this aquatic vegetation, metacercariae excyst in the small intestine.

How do the immature adults get to the liver? _________________________________________________________________________________

Adults wander within the liver for some time before reaching the bile ducts.

Adults reach maturity in 3 months.

Pathology of Fasciola hepatica infections

Immature adults - ________________

________________________________

Pathology of Fasciola hepatica infections

Adults - presence in the bile ducts cause

1.

2.

3.

4.

Pathology of Fasciola hepatica infections

Problems in infected livestock - ___________________________________________________________________________________________________________________________________________________________

Infected livers are condemned in packing plants.

 

Diagnosis of Fasciola hepatica infections

ID eggs in fecal sample 

- unembryonated with distinct _________________________

- size:

(Note: A false ID can occur in a person who has eaten an infected cow or sheep liver. Eggs will be passed through the digestive tract.)

Fasciola hepatica infections

TREATMENT -

PREVENTION -

Fascioloides magna – deer liver fluke

Definitive hosts -

Parasite is very large and fleshy.

Fascioloides magna – deer liver fluke

LIFE CYCLE is similar to that of Fasciola hepatica

• eggs released in deer feces into water

• miracidium hatches and penetrates snail - snail intermediate host in Wisconsin is Lymnaea

• sporocysts and rediae in snail produce cercariae

• free-swimming cercariae attach to aquatic plants

• metacercariae form on aquatic plant

• deer becomes infected by eating aquatic plant containing metacercariae

• immature adults migrate up common bile duct into liver tissue

Fascioloides magna – deer liver fluke

Adults occur within the ___________________________ (not bile ducts) and cause considerable damage.

Worms become encapsulated by fibrous tissue resulting in an extensive ___________________________.

Fasciolopsis buskiCommon parasite of ______________________________ in the Orient – SE Asia to India and the Pacific Islands.

It is estimated that over 10 million persons are infected with this parasite.

 

Morphology of Adult Fasciolopsis buski

Size: length 20-75 mm long and 20 mm wide

Adult is somewhat similar to Fasciola hepatica but differs by:

(1)

(2)

(3)

 

Morphology of Adult Fasciolopsis buski

Other structures are distinct:

________________________

________________________

________________________

________________________

________________________

Life Cycle of Fasciolopsis buski

Life Cycle is similar to that of Fasciola hepatica except that adults inhabit the __________________________________ (not the liver)

Dogs and pigs are common reservoir hosts. Thus, is is a _________________

Life Cycle of Fasciolopsis buski

Human infections are associated with eating ________________________________

________________________________

Common plants are ________________________________

_______________________________

Pathology of Fasciolopsis buski

1. ____________________________________________ of the small intestine at the attachment site. Causes a chronic _______________________________

2. Heavy infections can _________________________________________________

3. __________________________ - parasite's waste metabolites are absorbed and poison body cells. May cause death.

Pathology of Fasciolopsis buski

Diagnosis: _________________ ___________________________

These cannot be distinquished from Fasciola hepatica (unembryonated with distinct operculum).

Treatment: Drug treatment is available. Drug of choice is ___________________________

Prevention -

Family OpisthorchiidaeClonorchis sinensis - Chap. 18, p. 287-291

Chinese liver fluke is an important parasite of humans in the __________________________________________________________________

19 million persons infected in 1947 - more now

Disease is Clonorchiasis.

Morphology of Clonorchis sinensis adult

Adults are elongate, 8-25 mm long.• Characteristic feature: __________________________________________ at the posterior end.

Morphology of Clonorchis sinensis adult

Other organs are distinct: _________________________________________________________________________________________________________

__________________________________________

Life Cycle1. Adult Clonorchis inhabits the _______________________. 2. Adult releases up to 4,000 eggs/day. Eggs are released into the _______________ _____________________ _____________________

3. Egg is released into an aquatic habitat where ________________________________________________(first intermediate host)

- this snail does not occur in North America 

Life Cycle4. Within the snail, the miracidium hatches into a mother sporocyst mother rediae cercariae.

5. Free-swimming cercariae attach to _________________ (2nd intermediate host), burrow into the muscle, and become ________________________

Life Cycle 6. Human becomes infected by ________________________________________________________________________________________________

7. Metacercariae excyst in the human duodenum.

Immature adults migrate via ________________________________________________

Adults are mature in 1 month.

Epidemiology

Life cycle is initiated by ________________________________________ ______________________________________especially fish ponds where both snails and carp are present. Privys are often built over the fish pond.

Epidemiology

In the Orient, fish is the main source of protein. - raw fish is considered a delicacy (sushi, sashimi) - poor people cannot afford fuel to cook fish

Epidemiology

Metacercariae in carp can withstand pickling, salting, smoking, and drying.  Cases of clonorchiasis in the U.S.?

 Reservoir hosts?

Carp second intermediate hosts

Pathology

1. Hyperplasia of the _________________________causes extreme thickening of the bile duct.

 2. Bile ducts become surrounded by _________________________ resulting in pipestem fibrosis.

Pathology

3. Bile duct may perforate and eggs can get into the liver parenchyma where they are surrounded by scar tissue resulting in ________________________

4. Infection may also stimulate ________________________

 

White areas show cirrhosis in infected liver

Diagnosis and Treatment

DIAGNOSIS –

- these are small with operculum at constricted end

-we’ll measure them in lab to find out size!

TREATMENT -

Why is Clonorchis not in the U.S.?

1.

2.

 

Family DicrocoelidaeDicrocoelium dendriticum - p. 277-279

Adults of the lancet fluke are parasitic in the bile ducts of some 50 different species of mammals

This is _______________________________________

Common definitive hosts are: __________________________ __________________________________________________.

Human cases?

Morphology of Dicrocoelium dendriticum adult

Adults are small, 6-10 mm in length.

Characteristic feature is the ______________________________________________________

- testes are lobed and tandem

- posterior to the testes is _________________________

Posterior portion of body consists of an ___________________________

Life Cycle of Dicrocoelium dendriticum

1. Adults occur in the ______________________________________________and release eggs in the bile and eggs are deposited __________________ in the definitive host's feces.

2. Fecal material is fed on by a _______________________ (1st intermediate host) that ingests the eggs.

Life Cycle of Dicrocoelium dendriticum3. Eggs hatch inside the snail releasing the _________________________. These become mother sporocysts which produce daughter sporocysts which produce _________________________.

(no redia stage)

4. Cercariae are released from the snail in thick mucus trails called _________________________ formed as the snail crawls along.

Life Cycle of Dicrocoelium dendriticum

5. Slime balls are eaten by an _____________________ - 2nd intermediate host.

- Most metacercariae occur in the ant's body cavity but a few metacercariae encyst in the _________________________

 - These metacercariae cause an _______________________ _________________________ causing the ants to climb to the top of plants where they are easily accessible to grazing mammals.

Life Cycle of Dicrocoelium dendriticum

6. Grazing mammal ingests ant, metacercariae excyst in duodenum, and worms migrate up common bile duct into the liver.

Differences in life cycle compared to other trematodes

1. Life cycle occurs ______________________

2. Parasite causes a ______________________ of the ant second intermediate host to increase the chances that the life cycle will be completed

Pathology of Dicrocoelium dendriticum infections

Pathology is similar to that of other liver flukes involving

1.

2.

Pathology of Dicrocoelium is generally not as severe as that caused by other liver flukes.

Drug treatment is available.

Why are human infections with Dicrocoelium rare?

Movie from “The Body Snatchers” on first two parasites changing behavior of intermediate hosts

BEHAVIORAL CHANGES OF INTERMEDIATE HOSTS CAUSED BY PARASITES:

1.Pumpers – snails infected with larvae of a bird trematode

2. Ants infected with metacercariae of Dicrocoelium dendriticum

3.Toxoplasma gondii bradyzoites change the behavior of mice and rats. Infected mice and rats show a marked decrease in their natural fear of cat odors and actually seek out cat odors (changes that tend to make these rodents more likely to be eaten by a cat).