ICL 3.1: Worms & Cestodes Flashcards
which groups are at risk for parasite infection?
- minorities
- immigrants
- poor
- disadvantaged communities
what are the parasitic infections we are most worried about?
- chagas disease
- neurocysticerosis
- toxocariasis
- toxoplasmosis
- trichomoniasis
what are the two groups of helminths?
- platyhelminths = flatworms –> cestodes (tapeworms) and trematodes (flukes)
- nemathelminthes = roundworms –> nematodes
how are cestodes transmitted?
cestodes = tapeworms
ALL cestodes are transmitted by ingestion
what are the characteristics of the cestode body?
cestode = tapeworm
may be METERS long
scolex has hooks, rostellum, and suckers
neck region = proglottids form
strobila = string of proglottidesthat are immature near neck and mature are you get farther away
where are adult cestodes found in the body?
adults are found in the intestine
but virtually no clinical effect!!
what form of a cestode causes disease?
adults are found in the intestine with virtually no clinical effect
it’s the larvae that hatch from eggs after they’re eaten by intermediate hosts that are the problem
the larvae penetrate through intestinal wall into tissues!
the most damaging disease is caused by larvae
what is the diagnostic feature of cestode infection?
eggs or proglottids in feces
how are cestodes transmitted?
by ingestion!!!!
which cestodes are ingested and cause intestinal infection?
- T. solium
- T. saginata
- Dipiyllobothrium latum
- Diplydium caninum
what is the common name for diphyllobothriasis?
fish tapeworm
they’re a cestode = tapeworm
what is the largest human tapeworm?
diphyllobothrium latum = fish tapeworm
what are the definitive hosts of diphyllobothrium latum?
diphyllobothrium latum = fish tapeworm
humans, bears, minks & other animals
definitive host = an organism which supports the adult or sexually reproductive form of a parasite
what are the intermediate hosts of diphyllobothrium latum?
2 intermediate hosts: larval stages in water, picked up by water flea (crustacean), then by fish (source of human infection)
we eat the infected fish and that’s how we get sick
intermediate host = an organism that supports the immature or nonreproductive forms of a parasite
what’s the transmission cycle of diphyllobothrium latum?
- unembryonated eggs are passed in feces
- eggs embryonate in water
- coracidia hatch from eggs and are ingested by crustaceans
- procercoid larvae in body cavity of crustaceans
- infected crustaceans are ingested by small freshwater fish
- predator fish eats infected small fish
- humans eat raw/undercooked infected fish
- adults end up in the small intestine
- proglottids release immature eggs
cycle starts over
what are the symptoms of diphyllobothrium latum?
virtually no clinical effect
epigastric pain, nausea, vomiting
occasional intestinal obstruction, diarrhea, and abdominal pain
very occasionally it can cause low levels of B12 = megaloblastic anemia
how do you diagnose diphyllobothrium latum?
operculated eggs with knob on the bottom of the shell or proglottids in feces
egg looks like a white oval with white speckles all inside it
how do you treat diphyllobothrium latum?
Niclosamide and Praziquantel
what are the definitive hosts of dipylidium caninum?
humans!!
pet-owners (cats and dogs)
children
what are the intermediate hosts of dipylidium caninum?
fleas
how do humans get dipylidium caninum?
humans get infected by ingesting fleas infected with cysticercoid
what is the life cycle of dipylidium caninum?
- proglottids are passed intact in the feces or emerge from perianal region of either animal/human hosts
- egg packets containing embryonated eggs are ingested by larval stage of flee
- oncospheres hatch from the eggs and penetrate the intestinal wall of the larvae – cysticercoid larvae develop in the body cavity
- adult flea harbours the infective cysticercoid
- host is infected by ingesting fleas containing cysticercoids
OR
animals can transmit the infected fleas to humans
- humans, normally children, acquire the infection by ingesting the infected flea
- adult in the small intestine –> the scolex attaches in intestine
what are the symptoms of dipylidium caninum?
virtually no clinical effect
can see abdominal discomfort, anal pruritus, and diarrhea
how do you diagnose dipylidium caninum?
eggs (colorless egg packets) or proglottids in feces
the eggs look like an oval egg with smaller circles inside the whole egg – the circles have a thick outer lining
how do you treat dipylidium caninum?
praziquantel
what is the common name for taenia saginata?
beef tapeworm
what is the common name for taenia solium?
pork tapeworm
what is the definitive host of taenia saginata?
human ONLY
adult tapeworm is in the intestine
what is the intermediate host of taenia saginata?
ox, cattle
larval form is in the muscle
how do people get infected with taenia saginata?
Humans do not get beef tapeworm from ingesting eggs, only by ingesting the larval form (in meat)
what is the life cycle of taenia saginata?
- eggs or gravid proglottids in human feces and passed into environment
- cattle become infected by ingesting vegetation contaminated by eggs or gravid progiottids
- oncospheres hatch, penetrate intestinal wall, and circulate to musculature of cow
oncospheres develop into cysticerci in muscle
- humans infected by ingesting raw or undercooked infected meat
- scolex attaches to intestine
- adults in small intestine
what is the definitive host of taenia solium?
human only!!!
adult tapeworm in intestine
aka pork tapework
how do humans get taenia solium?
by eating pork containing cysticerci!
what is the intermediate host of taenia solium?
pig or human!
cysticerci in muscle + organs= cysticercosis –> develops after eating eggs from human feces
what is the life cycle of taenia solium that causes intestinal infection?
- eggs or gravid proglottids in human feces and passed into environment
- cattle become infected by ingesting vegetation contaminated by eggs or gravid progiottids
- oncospheres hatch, penetrate intestinal wall, and circulate to musculature of pig
oncospheres develop into cysticerci in muscle
- humans infected by ingesting raw or undercooked infected meat
- scolex attaches to intestine
- adults in small intestine
what are the clinical symptoms of taenia saginata and taenia solium?
virtually no clinical effect
sometimes abdominal discomfort –> the main symptom is often the passage of proglottids trough the intestinal tract
T. solium taeniasis is less frequently symptomatic than T. saginata taeniasis
what is the most important feature of taenia solium?
the risk of development of cysticercosis
how do you diagnose taeniasis?
- eggs in the feces
the egg just looks like a plain oval that has a thick outer lining
- gravid proglottids
- scolex = rarely found
how do you treat taeniasis?
praziquantel
how do you prevent taeniasis?
cook you meat well
freezing meat at -20°C for at least 12 hours
sanitation = controlled disposal of human feces = keep out of water and vegetation!!
cattle or pigs must ingest grass contaminated with human feces to get infected!!
which cestodes are transmitted by ingestion and cause tissue infection?
- T. solium (cysticercosis)
2. echinococcosis granulosus
which parasite causes cysticercosis?
taenia solium = pork worm
what is the life cycle of T. solium when it causes cysticercosis?
- eggs of gravid proglottids in feces and passed into environment
- embryonated eggs are ingested by human host in feces….
- oncospheres hatch, penetrate intestinal wall and circulate to masculature
- cysticerci may develop in any organ but as more common in subcutaneous tissues and the brain and eye
what does cysticercosis cause?
caused by T. solium in tissues
common cause of seizures in developing countries
neurocysticercosis may account for at least 10% of seizures seen in some emergency departments and more than 2% of neurological or neurosurgical admissions
most persons who die from cysticercosis in the US are foreign born
what are the symptoms of cysticercosis?
the most frequently reported tissue locations are skin, skeletal muscle -> do not cause symptoms.
asymptomatic subcutaneous nodules and calcified intramuscular nodules can be encountered
death can occur suddenly
extracerebral cysticercosis can cause ocular, cardiac, or spinal lesions with associated symptoms.
what is cerebral cysticercosis?
aka neurocysticercosis
caused by T. solium
diverse manifestations including seizures, mental disturbances, focal neurologic deficits, and signs of space-occupying intracerebral lesions
how do you diagnose cysticercosis?
- antibody detection: immUnoblot and enzyme immunoassays to T. solium
- biopsy of the effected area
- high IgE and eosinophils***
- CT scan, MRI or x-rays to detect the lesions
how do you treat cysticercosis?
surgery –> removal of the cysticerci in the eye or in cases that are not responsive to drug treatment or to reduce brain edema
if asymptomatic, untrated larval infections often subside symptom wise within 2-5 years
how do you treat neurocysticercosis?
symptomatic treatment with anti-seizure medication
or you can use antiparasite drugs like albendazole or mebendazole and anti-inflammatory corticoids and anticonvulsants (when needed)
how do you prevent cysticercosis?
sanitation = Sanitation controlled disposal of human feces = keep out of water and vegetation!!
this is so important because the ONLY way to develop cysticercosis is to eat human feces contaminated with T. solium eggs
what’s the common name for echinococcus granulosus?
hydatid worm
what is the definitive host of echinococcus granulosus?
small intestine of dogs
what is the intermediate host of echinococcus granulosus?
live stock = sheep, goat, swine
humans
what disease does echinococcus granulosus cause?
it causes hydatid disease in humans
humans get echinococcosis disease by eating dog feces (eg. on contaminated food)
what is the infection cycle of echinococcus granulosus?
- adult in small intestine of dog (definitive host)
- embryonated egg in feces
at this point a human could eat the egg in the feces (intermediate host) –> will cause cysts in liver, lungs, etc.
- sheep ingests eggs in feces (intermediate host)
- oncosphere hatches, penetrates intestinal wall
- hydatid cyst in liver, lungs
- dog ingests cysts in organs of dead infected sheep, goat, swine, etc.
- scolex attaches to intestine of dog
what are the symptoms of echinococcus granulosus?
silent for years
hepatic involvement = abdominal pain, a mass in the hepatic area, and biliary duct obstruction
pulmonary involvement = chest pain, cough, and hemoptysis
rupture of the cysts can produce fever, urticaria, eosinophilia, increased IgE, and anaphylactic shock, as well as cyst dissemination
in addition to the liver and lungs, other organs may be affected (brain, bone, heart)
how do you diagnose echinococcus granulosus?
- antibody detection –> Indirect hemagglutination (IHA), indirect fluorescent antibody (IFA) tests, and enzyme immunoassays (EIA)
- hydatid Cyst. ultrasonography and/or other imaging techniques supported by positive serologic tests
how do you treat echinococcus granulosus?
- surgery to remove parasite mass (not usually 100% effective)
there’s also danger from potential of a ruptured cyst which could release antigen and cause shock
after surgery, use albendazole or mebendazole to keep the cyst from recurring
how do you prevent echinococcus granulosus?
- denying sheep dogs access to carcasses of infected sheep
- obligatory testing and treatment of all sheep dogs
- prevention of contact of children with possibly infected sheep dog
- widespread education on the danger and method of spread of hydatid disease
