ICL 3.2: Trematodes Flashcards
what’s the common name for trematodes?
flukes
they’re a type of helminths –> platyhelminths specifically = flatworms
which trematodes are transmitted by ingestion and cause tissue infection?
- fasciola hepatica
2. paragonimus westermani
which trematodes are transmitted by contact and cause tissue infection?
- schistosoma japonicum
- schistosoma mansoni
- schistosoma haematobium
what kind of infection do trematodes cause?
tramatodes are transmitted by either ingestion or contact
but they ALL always lead to tissue infection
which groups are at risk for trematode infection?
- immigrants
- tourism/foreign travel
- military
major contributor to morbidity in developing countries
how do humans get schistosomiasis?
humans get infected by contact through the skin by cercariae
infection is by water-born cercaria – hyaluronidase helps in skin penetration
cercariae = a free-swimming larval stage in which a parasitic fluke passes from an intermediate host (typically a snail) to another intermediate host or to the final vertebrate host
which 3 parsites cause schistosomiasis in humans?
- Schistosoma mansoni (mesenteric veins)
- S. japonicum (mesenteric veins)
- S. haematobium (veins of the bladder)
they are all transmitted by contact and cause tissue infection
what is the life of schistosomes?
- bacteria in the feces or urine
- eggs hatch releasing miracidia
- miracidia penetrate snail tissue
- sporocysts in snail
- cercariae released by snail into water and free swimming
- cercariae penetrate human skin (definitive host)
- cercariae lose tails during penetration and become schistosomulae
- circulation
- migrate to portal blood in liver and mature into adults
- paired adult worms migrate to mesenteric venules of bowel/rectum and venous plexus of bladder where they are shed in stools and urine
what are the key points in the schistosome life cycle?
adults live 2-30 years inside the body!!!
100s-1000s eggs are released each day and migrate into intestinal lumen or bladder – eggs produce proteases allowing for this tissue migration
however ~50% “eggs” die within host tissue and account for most pathology = inflammatory response
which enzyme helps schistosomes penetrate human skin?
hyaluronidase
which tissue does schistosoma mansoni infect?
mesenteric veins
which tissue does schistosoma japonicum infect?
mesenteric veins
which tissue does schistosoma haematobium infect?
veins of the bladder
what are the effects on the body caused by S. mansoni and S. japonicum?
- portal hypertension
- ascites** (like swollen african kid stomach)
- esophageal varicose veins
- liver fibrosis
what is pipestem fibrosis? which parasite is it caused by?
Longitudinal sections of portal canals in which there is a great increase in the amount of fibrous tissue around the vessels and bile ducts - due to large numbers of schistosome eggs
caused by S. mansoni and S. japonicum
what are the effects on the body caused by schistosoma haematobium?
- hematuria in early disease
- eventual fibrosis of bladder and obstructive uropathy
- rarely renal failure and hydronephrosis
- rarely bladder carcinoma
how do you diagnose a schistosome infection?
- eggs in feces or urine are characteristic and diagnostic
S. mansoni = big lateral spine sticking out from the long side of the body
S. japonicum = small lateral spine
S. haematobium = terminal spine sticking out from one of the ends
- immunodiagnosis = ELISA, IFAT, RIA, IHA
how do you treat a schistosome infection?
praziquantel (PZQ) and oxamniquine (OXQ)
effective, but resistance increasing
how do you prevent schistosome infection?
- avoid swimming or wading in freshwater when you are in countries in which schistosomiasis occurs –> swimming in the ocean and in chlorinated swimming pools is safe
- drink safe (boiled / filtered) water
- sanitation = avoid excretion into open water where snails live
- education
- snail reduction using molluscicides, biological control
what’s the common name for paradonimus westermani?
lung fluke
so it’s a trematodes
what is the life cycle of paradonimus westermani?
- unembryonated eggs are released in sputum or in feces
- embryonated eggs
- miracidiae hatch and penetrate snail
- snail: sporocysts –> rediae –> cercariae
- cercariae invade the crustacean and encyst into metacercariae
- humans ingest inadequately cooked or picked crustaceans containing metacercariae
- excyst in duodenum
- adults in cystic cavities in lungs lay eggs which are excreted in sputum; alternately eggs are swallowed and passed with stool
how is paradonimus westermani transmitted?
consumption of raw/undercooked seafood
Asia/South America, imports??
where is paradonimus westermani found in the world?
paragonimus spp. are distributed throughout the Americas, Africa and southeast Asia
paragonimus westermani is distributed in southeast Asia and Japan
what are the symptoms of paradonimus westermani infection?
acute = diarrhea, abdominal pain, fever cough, pulmonary abnormalities, eosinophilia
chronic = pulmonary manifestations: cough discolored sputum, expectorated clusters of reddish brown eggs, not blood, radiographic abnormalities (pseudeotubercules)
how do you dignaose paradonimus westermani infection?
- eggs in stool/sputum; not present until 2-3 months after infection
egg looks like a grown blurry pear-shaped egg
- immunodiagnosis – especially useful to differentiate paragonimiasis from TB in Indochinese immigrants
how do you treat paradonimus westermani infection?
praziquantel
what’s the common name for fasciola hepatica?
liver fluke
how is fasciola hepatica transmitted?
consumption of raw/undercooked vegetables
solution: freezing below -10 C or heating above 60 C
where can you find fasciola hepatica in the world?
worldwide
F. hepatica are found in areas where sheep and cattle are raised, and where humans consume raw watercress (including Europe, the Middle East, and Asia)
what’s the life cycle of fasciola hepatica?
- unembryonated eggs are passed in feces
- embryonated eggs in water
- miracidia hatc, penetrate snail
- snail: sporocysts –> rediae –> cercariae (intermediate host)
- free-swimming cercariae encyst on water plants
- metacercariae on water plant are ingested by human, sheep or cattle (definitive hosts)
- excyst in duodenum
- adults in hepatic biliary ducts
what are the symptoms of fasciola hepatica infection?
acute = diarrhea, abdominal pain, fever, vomiting, enlarged liver
chronic = intermittent blockage of the bile duct and inflammation
how do diagnose fasciola hepatica infection?
eggs in stool
eggs are blurry inside oval shaped
there’s a thin operculum at one end = flap
how do you treat fasciola hepatica infection?
triclabendazole
which trematodes are trematodes that cause tissue infection but in the wrong host?
schistosoma - cercarial dermatitis
what is cercarial dermatitis?
infection of skin by cercariae that are not adapted to humans (e.g. bird schistosomes)
cercariae penetrate skin (pin prick), fail to form functional schistosomulum and die
this causes an inflammatory reaction in skin, small red spot in 30 min, increases in size next 24-30 hrs, resolves in 4-7 days –> looks like little red allergy dots everywhere
treatable with anti-inflammatory drugs
which groups are at risk for cercarial dermatitis?
it’s a serious problem locally for swimmers in ponds, quarries, etc, esp near shore (limit waterfowl/treat with molluscicides)
what is the life cycle of schistosomes in the wrong host that cause cercarial dermatitis?
- eggs are passed in the feces of birds
- eggs hatch and liberate miracidia
- the parasite develops in a molluscan intermediate host (snail)
- humans are exposed to the dermatitis-producing cercariae
or cercariae penetrate the skin of the birds swimming in the water and migrate to blood vessels to complete the cycle
