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34 Cards in this Set

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What are the two groups of Flatworms?`
1. Trematodes
2. Cestodes
Flatworms are called Platyhelminthes, and they do not possess a digestive tract.
What are Trematodes?
These are known as flukes, and include the freshwater dwelling schistosomes. Both male and females exist and mate within humans(not in the digestive tract)
All have a water snail species as an intermediate host.
What are cestodes?
These are tapeworms and live and mate within the human digestive tract. each tapeworm has both male and female sex organs(hermaprodites) so individual worms can produce offspring by themselves.
What are Schistosoma?
These are bloodflukes. Schistosomal infections are common, second only to malaria as a cause of sickness in the tropics.
They are found in freshwater, and penetrate through exposed skin and invade the venous system where they mate and lay eggs.
What are the three major Schistosoma species worldwide?
1. S. japonicum
2. S. mansoni
3 S. haematobium.
What is the Schistosoma life cycle?
1. It begins when their eggs hatch in fresh water. Larvae emerge and swim until they find a freshwater snail.
2. After maturing in the snail, larvae are released and are now infectious to humans.
3. Mature schistosomal larvae called cercariae, which look like tadpoles penetrate through exposed skin and travel to the intrahepatic portion of the portal venous system.
4. At this location the schistosomes mature, and through the venous system surrounding the intestines or bladder, they will lay eggs, either with stool or urine.
Schistosoma adult worms in the venous system are able to survive and release eggs for years, since they are not killed by the immune system. TRUE/FALSE
What is molecular mimicry?
It is the incorporation of host antigens onto their surface, which fools the host immune system into thinking that the Schistosomes are not foriegn.
Schistosoma cercariae(mature larvae) and eggs briskly stimulate the immune system, and are responsible for the systemic illness caused by this infection. TRUE/FALSE
Schistosomiasis has 3 major disease syndromes that occur sequentially. What are they?
1. Dermatitis(cercariae penetrate skin)
2. Katayama fever as the grown adults begin to lay eggs.
3. Chronic fibrosis of organs and blood vessels from inflammation around deposited eggs.
What happens during Katayama fever?
This follows 4-8 weeks later with symptoms that can include fever, hives headache weight loss and cough. Lymph node enlargement is common as is eosinophilia.
What happens to eggs laid by adults that are not excreted with stool or urine?
They are whisked off by the bloodstream, where they are deposited in the liver, lung or brain. The immune system will react against these eggs walling them off as granulomas.
The venous walls of the liver develop fibrosis which cause blockage of the portal venous system(portal hypertension). Ulcers and brain lesions have been noted.
How is diagnosis acheived?
It is based on the demonstration of eggs in stool or urine samples and high eosinophil counts in the blood.
What is the treatment?
Praziquantal. The death of the schistosomes will however evoke a vigorous immune response.
What is a proglottid?
The tapeworm is long and flat consisting of segments called proglottids.
What is the scolex?
It is the most anterior segment of the tapeworm(head) which has suckers.
It also will have immature proglottids and mature proglottids that have both male and female sex organs.
Gravid proglottids contain fertilized eggs.
How are tapeworm infections treated/
Praziquantel or Niclosamide
Albendazole for Taenia soilium larval cysticerci.
What is Taenia solium?
Humans acquire this by ingestion of undercooked pork infected with larvae.
The tapeworm attaches to the mucosa of the intestine via hooks on its scolex and grows to a length of 2-8 meters.
What is the pathogenesis of Taenia solium?
1. When pigs graze on fields contaminated with the egg infested human feces they become the intermediate host.
2. Eggs develop into larvae that disseminate through the intestine and into muscle.
3. In the animals muscle tissue, the larvae develop into another larval form, the cysticercus. It is a round fluid filled bladder with the larval form within.
4. When a human ingests insufficiently cooked pork, the larval cysticercus converts to the adult tapeworm in the intestine and the cycle continues.
What is Cysticercosis?
This occurs when humans play the role of the pig and ingest eggs rather than encysted larvae.
These eggs hatch within the small intestine and the larvae migrate throughout the body, where they penetrate into tissue and encyst forming cysticerci.
The larvae often encyst in the brain and skeletal muscle.
Cysticerci in the brain tend to cause more symptoms and this condition is called Neurocysticercosis. TRUE/FALSE
TRUE. There are usually 7-10 cysts in the brain causing seizures, hydrocephalus and neurological deficits.
What happens to these brain cysts?
They grow slowly and after 5-10yrs, they begin to die and leak their fluid contents. Local inflammation, deficits and seizures are common as a result of this.
How is diagnosis acheived?
Cat scan or biopsy of infected tissue, which may reveal calcified cysticerci.
How is Taenia solium treated?
It is the most common cause of seaizures in these areas.
Mexico central and South america, and the Phillipines.
What is Taenia saginata?
It has the exact same life cycle as T. solium, except that humans do not develop cysticerci when they ingest eggs, as do the intermediate hosts(cattle). The infection is relatively benign.
What is Diphyllobobothrium latum?
This is a fish tapeworm that can grow up to 45 meters in length. It is acquired by ingesting larvae in raw freshwater fish.
What is the cycle of D. latum?
It involves a human and 2 freshwater intermediate hosts, a crustacean and a fish.
2. The adult worms in the human intestine drop off their gravid proglottids loaded with eggs.
3. The eggs end up in water, they convert to a motile larvae form, which is then ingested by a freshwater fish(trout, salmon, pike) which is then ingested by a human.
What are the symptoms?
Few symptoms are provoked, although the parasite can absorb large amounts of vitamin B12.
What is Hymenolepis nana?
This is the smallest tapeworm that infects humans(15-50mm) and has a simple life cycle. Humans ingest eggs that grow into adult tapeworms, and these worms pass more eggs that are ingested again.
What is Echinococcus granulosus and multiocularis?
It is also called Hydatid disease. Dogs and sheeps perpetuate the life cycle of E. granulosus and the human isonly a dead end in the cycle.
Ingested eggs hatch in the intestine and develop into larvae. After penetrating through the intestinal wall, the larvae disseminate throughout the body. many will concentrate in the liver, lungs, brain and kidney.
What is the Hydatid cyst?
Each larvae forms a single, round fluid filled hydatid cyst. These undergo asexual budding to form daughter cysts and protoscolices inside the original cyst. they can grow 5-10cm in size.
Do these cysts cause symptoms?
yes. They may compress the organ around them.
Humans are extremely allergic to the fluid within the cyst.
E. granulosus simply grow larger only to spread if they rupture. E. multiocularis cysts undergo lateral budding and spread. They may be misdiagnosed as tumors.
How is diagnosis made?
CAT scanning and tissue biopsy. Only 10% of hydatid cysts are symptomatic and treatment is difficult. surgical removal is often indicated.
How is therapy approached/
Treatment for months with Albendazole to kill the cysts is employed, though this alone is rarely curative.
The cyst is surgically exposed and some of the cyst fluid is carefully aspirated. saline Iodophore or Ethanol is next instilled into the cyst to make sure that the contents are dead.