Lec 9 - flukes Flashcards
Flatworm Tegument
- is a large, multi-nucleate cell layer that covers the body surface of these parasites.
- syncytial, meaning it’s made of fused cells with many nuclei, allowing for efficient coordination across the body surface
- epidermis is “sunken”, meaning it lies below the muscle layer, while the outer tegument extends above it and is cytoplasmic in nature
Describe a generalized life history of Paragonimus westermani
Eggs leave the human body
Passed in sputum (spit) or feces
In water, the eggs become embryonated (develop inside)
Miracidium hatches from the egg
Swims and penetrates a snail
Inside the snail:
Goes through sporocyst → redia → cercaria stages
(This is the first intermediate host)
Cercaria leaves the snail
Swims and invades a crustacean (e.g., crab or crayfish)
Encysts as a metacercaria (resting stage)
Human eats undercooked or pickled crab/crayfish
Ingests the metacercaria
Metacercaria excysts (breaks out) in the duodenum
Migrates through the body to the lungs
Adult flukes live in the lungs
Lay eggs in lung cavities
Eggs are either:
Coughed up in sputum, or
Swallowed and passed in feces
Describe a generalized life history of Clonorchis sinensis
Eggs are released in feces
Must reach freshwater to continue development.
Eggs are eaten by a freshwater snail (first intermediate host)
Inside the snail, the parasite undergoes asexual reproduction
→ Develops through: miracidium → sporocyst → redia → cercaria
Cercaria leaves the snail
Swims and penetrates a freshwater fish (second intermediate host)
Inside the fish, cercaria encysts in the muscle as a metacercaria (infective stage)
Humans eat raw or undercooked fish
Metacercaria is ingested
In the small intestine, the metacercaria hatches and migrates to the bile duct
Adult flukes live in the bile ducts, where they lay eggs
Eggs are excreted in feces, completing the cycle.
How can people avoid catching schisto?
- Drug treatment against adult worms
-Praziquantel - Limiting fecal contamination
-outhouses
- build in correct places! away from freshwater sources - Public edu - use the outhouses!
- Agriculture
-try & cut down aquatic vegetation
-put inorg. med. in irrigation channels to limit snail growth - Mollucticides, but risky
- Limit reservoir hosts
-use horses not oxes. as horses serve as a bad reservoir host. But this comes with inc personal wealth
SCHISTO HAS NOTHING TO DO WITH FOOD !
What is the importance of waste treatment in schisto?
Critically important in controlling Schistosoma infections because it directly interrupts the parasite’s life cycle.
snails are going to be infected by the eggs released by the definitive host’s waste and it’s generally in the feces / urine finding it’s way to freshwater. Without proper waste management such as outhouses, eggs continue to contaminate water, making reinfection and community-level transmission nearly impossible to control.
Outline the Schistosome life cycle IN SNAIL
- Eggs released in human feces or urine
- In water, eggs hatch - Miracidia
- Contacts snail
- In snail, miracidia transforms to sporocysts
- sporocysts produce cercaria directly
*NO REDIAE STAGE - acts as castrator for the snail - cercaria bursts out of the snail and swim until they contact bare human skin
Outline the Schistosome life cycle IN HUMAN
- Cercariae pierce the skin using enzymes
- cercaria sheds the tail as it immunogenic
- develop new tegument and are now Schistosomules
- enter BV and migrate through lungs, heart and liver
- While in lungs. worms feed on blood and learn to look like us
- decorate their tegument with self antigens
Describe why Schistosoma has a “unique” lifecycle among other digeneans
Only one intermediate host:
→ Unlike most digeneans that use two, Schistosoma uses only a freshwater snail.
No redia stage:
→ Inside the snail, it goes through sporocysts only, skipping the redia stage seen in many other flukes.
No second intermediate host or encysted stage:
→ There is no metacercaria or encysting in fish, plants, or crustaceans.
Swimmer’s Itch; its causes
Swimmer’s itch is caused by schistomes that are in Birds - that infect aquatic snails -> can cause a zoonotic infections on humans
common in area that there are migrating birds
○ Those cercharia are not used to our immune system
- They become attacked by our immune system
-This causes swimmers itch, u have granulocytes catches it right where it is
- very red and itchy
-what is happening, is an immune response: when penetrating the human skin, our immune system catches it, killing the parasite
-the parasite has not evolved to evade our immune system
Swimmer’s Itch; its control //
Avoid swimming in snail-infested areas, especially during warm months or early morning.
Towel off immediately after swimming to remove any cercariae before they burrow into the skin.
Life History of Fasciola Hepatica
- Adult fluke lives in bile ducts of the definitive host
- Eggs are released in the host’s feces into the enviroment
- In freshwater - eggs hatch miracidia
- miracidium penetrates a freshwater snail’
- inside the snail - the parasite undergoes ASEXUAL PRODUCTION (Sporocyst - redia - cercaria
- cercaria exit the snail and encyst on aquatic vegetation or float freely as metacercariae
- definitive host {livestock,human} becomes infected by eating vegetation contaminated with metacercariae
- metacercaria excysts in the small intestine - and travels to liver
- fluke matures in the bile ducts
Disease of Fascicole hepatica
Important species causing extensive damage to the ruminant farming, and human disease
In Livestock: it causes amnesia, inflammation, swelling
- decreased growth, milk production, and un useable livers for food
In humans: symptoms progress from fever, abdominal pain, anemia
The chronic phase can occur months/years after infections and can lead to significant abdominal pain and liver complications
- Can cause cancer in chronic
infections
- Adult migration around liver causes
tissue necrosis
Control of FH
-Avoid eating aquatic vegetation
- proper waste management
outhouses
-Minimize snail habitat - use inorganic materials in irrigation channels
Contrast Fasciola Hepatica with other Echinostomids
