Parasitology. Cestodes

Cestodes. Intestinal Tapeworms. Tissue Tapeworms

General Characteristics

flat and ribbon-like

hermaphroditic

no digestive track - absorbed nutrients from host food

produce little pathology

General Morphology

scolex

neck

proglottids

Scolex

orientation of worm

biological holdfast

not for support or feeding

hooks, rostellum, suckers

Neck

ares for growth of worm

area where proglottids bud off

undifferentiated stem cells

Proglottids

segments that are sexually immature, sexually mature, or gravid

gravid = are egg-filled

Strobilia

body of tapeworm minus scolex

chain of proglottids

How to tapeworms absorb nutrients?

across tegument

pinocytosis

diffusion/facilitated diffusion

active transport

Microtriches

microvilli that covers the tegument of cestodes and assist with nutrient absorption

Dwarf tapeworm

Hymenolepis nana

Hymenolepis nana Morphology

~1-3 inches

scolex - 4 suckers and hooks on rostellum

proglottids disintegrate in gut

Hymenolepis nana Life Cycle (direct)

ingestion of mouse pills or embryonated eggs (contaminated food/water)

oncosphere hatches→ cysticercoid

adults develop in small intestine

gravid proglottis disintegrates → eggs in gut

eggs leave through feces

Hymenolepis nana Life Cycle (indirect)

egg is ingested by insect

cysticerrcoid in insect

human/rodent host consume insect

(normal cycle continuous in host)

Hymenolepis nana Life Cycle (auto infection)

occurs if eggs remain and hatch in intestine

Hymenolepis nana Epidemiology

person to person contact

common in children

mouse pills infect humans or beetles

tenebrious beetle can be intermediate

Does Hymenolepiis nana need an intermediate host?

No

Hymenolepis nana Pathology

asymptomatic or mild symptoms

irritation to gut wall

allergic reaction to worm metabolites (diarrhea, headache, nervousness, dizzy)

Hymenolepis nana Diagnosis

eggs in stool

Hymenolepis nana Prevention

personal hygiene

mass chemotherapy

What is the reservoir host for Hymenolepis nana?

mice

When is Hymenolepis nana infective?

egg stage

Hymenolepis nana (LC pic)

Taenia saginata has _____ pathology, while Taenia solium has _____ pathology

little, high

Taenia saginata has _____ and Taenia sodium has _____

no hooks, hooks

Beef tapeworm

Taenia saginata

Taenia saginata Morphology

5-10 meters (but can grow up to 25)

scolex - 4 suckers, no hooks

proglottids - mobile and whole in stool; more than 15 uterine branches; migrate out of anus

Taenia saginata Life Cycle

cattle infected by contaminated vegetation

eggs hatch into oncospheres

oncospheres migrate to muscle

oncosphere → cyctercerci in muscle

humans consume raw/undercooked meat

scolex attaches to intestine

adult worm in small intestine

eggs or proglottids in feces

Taenia saginata Epidemiology

in feed lots → infected by lot workers

in grazing areas → polluted by sewage

endemic in all beef eating areas

Taenia saginata Pathology

little pathology; no weight loss

potential intestinal blockage

reaction to worm metabolites → diarrhea

Taenia saginata Diagnosis

proglottids in stool

Taenia saginata Prevention

inspect beef

cook beef @ 56°C → denatures protein

no sewage in grazing areas

import canned, not fresh beef

When is Taenia saginata infective for humans?

cysticerci stage

When is Taenia saginata infective for cattle?

egg stage

What is the intermediate host for Taenia saginata?

cattle/cows

Cysticercus bovis

intermediate larval stage of Taenia saginata in cattle; not in humans

Taenia saginata (LC pic)

Pork Tapeworm

Taenia solium

Taenia solium Morphology

8-10 meters

scolex - 4 suckers; hooks

proglottids - less than 15 uterine branches

Taenia solium Life Cycle

humans ingest raw/undercooked meat

scolex attaches to intestine

adults in small intestine

eggs/proglottids in feces

pigs ingest contaminated food/water

oncospheres hatch and migrate to muscle

oncosphere → cysticerci in pig muscle

*can cause cysticercosis in humans if eggs ingested*

Taenia solium Epidemiology

areas with high pork consumption

areas with lax inspection

Taenia solium Pathology (intestinal)

asymptomatic - mild symptoms

allergic reaction to worm metabolites → diarrhea

Taenia solium Pathology (cysticercus cellulosae)

encystment → calcification → dead end (intramuscular)

no encystment → grapelike cluster → Jacksonian epilepsy (brain)

floater in vitreous humor, no encystment → enters sub retinal space (eye)

death of organism → inflammation → loss of eye (eye)

encystment (soft tissues)

Cysticercus cellulosae

ingestion of eggs → onchosphere hatches in gut → enters circulation → travel to any organ

Taenia solium Diagnosis

proglottids in feces for adult worms (intestinal)

X-ray, CT scans, MRI (cysticercus cellulosae)

Taenia solium Prevention

proper disposal of feces

cook/freeze pork

inspect pork

What type of host are humans for Taenia solium?

definitive - consumption of cysticerci in uncooked/raw pork

accidentally intermediate - autoinfection or consumption of eggs

What is the intermediate host for Taenia solium?

pigs

When is Taenia solium infective for pigs?

egg stage

When is Taenia solium infective for humans?

egg stage (cysticercus cellulosae)

cysticerci stage (taeniasis)

Taenia solium (LC pic)

Fish tapeworm

Diphyllobothrium latum

Diphyllobothrium latum Morphology

5-10 meters

long lived (25-30 years)

scolex - bothrium (leaf-like suckers)

Diphyllobothrium latum Life Cycle

unembryonated eggs in feces

embryonate in water

eggs hatch into coracidia

copepod ingests coracidium

coracidium → procercoid larvae in body cavity

infected copepod eaten by small fish

procercoid → plerocercoid larvae in small fish

small infected fish eaten by larger predator

humans consume undercooked/raw fish

adults in small intestine

proglottids release immature eggs

unembryonated eggs in feces

Diphyllobothrium latum Life Cycle Stages

eggs

coracidium

procercoid larvae

plerocercoid larvae

adult worm

Diphyllobothrium latum Epidemiology

temperate regions with fresh water fish consumption

Great Lakes & Pacific Northwest

Finland, Scandinavia, Baltic region

Diphyllobothrium latum Pathology

mild attachment damage

allergic reaction to metabolites

has affinity for vitamin B-12 → pernicious anemia

Diphyllobothrium latum Diagnosis

eggs in stool

Diphyllobothrium latum Prevention

cook fish

prevent sewage from contaminating water

When is Diphyllobothrium latum infective to humans?

plerocercoid stage

What are the intermediate hosts for Diphyllobothrium latum?

copepods → small fish → large predatory fish

Diphyllobothrium latum (LC pic)

Unilocular Hydatid Disease

Echinococcus granulosus

Echinococcus granulosus Morphology

very small - ¼ inch long

scolex - neck - 3 proglottids (immature, mature, gravid)

Enchinococcus granulosus Life Cycle

embryonated eggs in feces

sheep (or humans) ingest eggs

oncosphere hatches

penetrate intestinal wall and migrate

hydatid cyst in organs (heart, lung, etc)

dog ingests cysts from sheep meat/organs

cyst → protoscolex

scolex attaches to intestine

adults in small intestine

eggs in feces

Echinococcus granulosus Life Cycle Stages

egg

oncosphere

hydatid cyst

protoscolex

adult worm

Enchinococcus granulosus Epidemiology

any place with sheep

Echinococcus granulosus Pathology

cysts expand uniformly

mechanical damage & pressure atrophy (liver)

cysts in brain/heart valves/lungs

allergic reaction to hydatid fluid → anaphylaxis

Echinococcus granulosus Diagnosis

observation

X-ray, CT scan, MRI

Echinococcus granulosus Prevention

treat dogs

cook sheep organs before feeding to dogs

What is the definitive host of Echinococcus granulosus?

dogs

What is the intermediate host of Echinococcus granulosus?

sheep

What type of host are humans to Echinococcus granulosus?

accidental intermediate hosts; dead-end hosts

When is Echinococcus granulosus infective to definitive host?

cyst stage

When is Echinococcus granulosus infective to intermediate host?

egg stage

Echinococcus granulosus (LC pic)

Alveolar hydatid disease

Echinococcus multilocularis

Echinococcus multilocularis Morphology

same as E. granulosus

very small

scolex - neck - 3 proglottids (immature - mature - gravid)

Echinococcus multilocularis Life Cycle

eggs in feces

rodents (or humans) ingest eggs

oncosphere hatches

penetrate intestinal wall and migrate

multi-chambered hydatid cyst in liver (sometimes other organs)

dog/fox ingests cysts from rodent meat/organs

cyst → protoscolex

scolex attaches to intestine

adults in small intestine

eggs in feces

Echinococcus multilocularis Epidemiology

northern hemisphere (Europe, China, Russia, Japan)

eating wild blackberries/blueberries/mushrooms contaminated with eggs

Northern U.S.

Echinococcus multilocularis Pathology

hydatid cyst that expands to create multiple chambers → multi-locular

slow - 5 to 15 years

mainly in liver, can affect other organs

cavitation → organ is replaced by cyst

Echinococcus multilocularis Diagnosis

indirect - X-ray, CT scan, MRI

liver function tests

observation

Echinococcus multilocularis Prevention

treat/control infected dogs

wash fruits

What are the intermediate hosts for Echinococcus multilocularis?

moles, voles, rodents

What are the definitive hosts for Echinococcus multilocularis?

dog, fox

What type of hosts are humans for Echinococcus multilocularis?

accidental intermediate hosts

Echinococcus multilocularis (LC pic)

Why do E. multilocularis and E. granulosus manifest differently?

multilocularis: weak/thin cyst wall → pressure makes it bulge out → multilocular

granulosus: strong/thick cyst wall → grows uniformly → unilocular

When is Echinococcus multilocularis infective to intermediate host?

egg stage

When is Echinococcus multilocularis infective to definitive host?

cyst stage