Trematodes and Cestodes

Question 1

List the trematodes and cestodes:

Answer 1

• Diphyllobothrium latum (broad fish tapeworm)
• Taenia saginata (beef tapeworm)
• Taenia solium (pork tapeworm)
• Schistosoma mansoni (trematode)
• Schistosoma haematobium (trematode)
• Schistosoma japonicum (trematode)
• Swimmer’s itch.

Question 2

Life cycle of Dephyllobothrium latum (broad fish tapeworm)?

Answer 2

30 years - 10-30 feet

Eggs water –> coracidium injested by Copepod (become procercoid stage) –> then eaten by minnow (encysts in muscles (Pleurocercoid)

From here, bigger things eat minnows, get up to trout/salmon

Poorly-cooked freshwater fish

Question 3

Pathogenesis of Dephyllobothrium latum (broad fish tapeworm)?

Answer 3

Pernicious anemia (worm competes with host for B12)

Usually 1 worm; mild manifestations

Question 4

Epidemiology of Dephyllobothrium latum (broad fish tapeworm)?

Answer 4

Russia, Sweden, Minnesota, Wisconsin, Pacific salmon (sushi)

Raw fish, sushi are big

Question 5

Diagnosis / Treatment of Dephyllobothrium latum (broad fish tapeworm)?

Answer 5

Demonstrate eggs / proglottids in stool

Praziquantel (and B12)

Question 6

Life cycle of Taenia saginata?

Answer 6

Small intestine in human –> proglottids pass in feces –> eggs in soil –> cattle graze

Oncosphere lodges in cow intestine –> blood/lymph to muscles (now called cysticercus)

Undercooked meant

Question 7

Pathogenesis of Taenia saginata?

Answer 7

Present singly; Concomitant immunity (one tapeworm prevents another, really) (once worm is in, Ab to other parasites as well)

Mostly asymptomatic

Question 8

Diagnosis / Treatment of Taenia saginata?

Answer 8

Gravid proglottids in feces (but can’t tell Taenia eggs from one another)

Praziquantel (90% cure rate)

Question 9

Life cycle of Taenia solium?

Answer 9

• Contaminated food/drink from human feces
• Reverse peristalsis: eggs to stomach
  Bonus! Oncosphere –> penetrates wall –> mesenteric veins –> cysticerci in brain, eye, muscle, lungs

Nodules (cysticercus)

Question 10

Pathogenesis of Taenia solium?

Answer 10

Few problems caused by adults in the intestines

Cysticercosis: severity depends on number and location

• MAIN SITE is subcutaneous connective tissue
• Ocular cysticercosis (damage retina/iris –> blindness)
• Brain (neurocysticercosis)
• Sudden epilepsy

Question 11

Diagnosis / Treatment of Taenia solium?

Answer 11

Find gravid proglottids in feces

Cysticercosis: soft tissue x-rays or CT to visualization
- Albendazole, cysticercosis surgery
- Steroids to minimize inflammation
Praziquantel for intestinal worms
Steroids to minimize inflammation

Question 12

Epidemiology of Taenia solium?

Answer 12

Mexico, C./S. America, Africa, East Asia

• Orthodox Jewish community in New York City (illegal Hispanic housekeepers)
• Migrant workers, often

Question 13

Brief overview:

Schistosoma mansoni

Answer 13

• Veins around intestines
• Africa, S. America, Carribean
• Biomphalaria snails

Question 14

Brief overview:

Schistosoma haematobium

Answer 14

• Veins (bladder)
• Africa / Near East
• Bulinus snails

Question 15

Brief overview:

Schistosoma japonicum

Answer 15

• Mesenteric veins
• China, Philippines
• Oncomelania snails (freshwater)

Question 16

Life cycle of Schistosoma?

Answer 16

• Eggs excreted from human (eggs are diagnostic)
• Miracidia inside (free larvae that must find snail)
• Asexually amplifies in snail
• Free-swimming cercariae (infective in humans) - penetrate unbroken skin
• Mature/mate in the liver
• Final place depends on species (like the veins; produce eggs 20-30 years)

Question 17

Pathogenesis of Schistosoma?

Answer 17

Eggs cause disease; Adult worms (antigenic mimicry)

• Papule at penetration site
• Acute phase (egg-laying): FEVER, discomfort, pain
• Chronic phase: Fibrosis of intestines (if eggs there) - thicken and lose fxn; Granuloma if in liver/spleen - block blood flow –> portal hypertension, hepatosplenomegaly

S. haematobium causes ulceration of bladder (bladder cancer)

Question 18

Diagnosis / Treatment of Schistosoma?

Answer 18

Eggs in feces for mansoni/japonicum
Eggs in urine for haematobium

Praziquantel (2 doses in 1 day)

Question 19

What is Swimmers itch? (a bird schistosome)

Answer 19

Cercariae enter human skin (we are unsuitable hosts); walled off and destroyed –> inflammation and rash

Antihistamine lotion; vigorous rubbing with towel reduces probability of penetration