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 Flukes 3 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 - a ccomplished 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
Life cycle of Fasciola hepatica 1. ________________________ 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 hepatica 4. 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 hepatica 6. 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 _________________________
(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.)
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 buski Common 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 Opisthorchiidae Clonorchis 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 Cycle 1. 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 Cycle 4. 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.
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
these are small with operculum at constricted end
we’ll measure them in lab to find out size!
Why is Clonorchis not in the U.S.? 1. 2.
Family Dicrocoelidae Dicrocoelium 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 dendriticum 3. 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:
Pumpers – snails infected with larvae of a bird trematode
Ants infected with metacercariae of Dicrocoelium dendriticum
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).