2.01 b - Intestinal Cestodes / Extraintestinal Cestodes Flashcards
Phylum Platyhelminths are also known as
Also known as flatworms
General description of Phylum Platyhelminths
- Dorsoventrally flattened, have solid bodies with no body cavity
- Internal organs are embedded in tissue called parenchyma
- No respiratory or blood-vascular systems
- At least one intermediate host is required to support larval development.
2 classes of Phylum Platyhelminths
2 classes: o Cestoda (tapeworms) o Digenea(trematodes or flukes)
Common name of Cestoda
tapeworms
Common name of Digenea
trematodes of flukes
All platyhelminths are hermaphroditic EXCEPT
blood flukes
Digestion of platyhelminths
- Tegument (external surface) - Highly absorptive, releases digestive enzymes at its surface from microtriches (specialized microvilli)
- Adult cestodes absorb all nutrients through the tegument because they have no mouth, digestive tract or vascular system
- Waste products are also released through the tegument
Physical description of class cestoda
- Commonly called tapeworms
- Long, ribbon-like, and flattened in cross section like a tape measure
- Adult may range from a few mm to 20 meters in length
- The anterior end of the adult (scolex) is modified for
attachment to the intestinal wall of the host - Strobila: Entire body of a tapeworm
Where do cestodes live?
- Adult cestodes live in the intestinal tract of the vertebrate
definitive host
- The larval stage inhabits the tissues of the intermediate host
Two physical compartments of cestodes
Scolex
o usually equipped with 4 cup-shaped suckers and some species have crown hooks to aid in attachment,
o less than 2mm long, although the whole body of the tapeworm can be 20m in body length
Strobila
o Entire body of a tapeworm
o Consists of segments known as proglottids
o Segments form by budding from the posterior end of the scolex
o Older mature segments move to the terminal end of the strobili as younger segments are produced
What is a scolex?
- anterior end of the adult cestode
o usually equipped with 4 cup-shaped suckers and some species have crown hooks to aid in attachment,
o less than 2mm long, although the whole body of thetapeworm can be 20m in body length
What is a strobila?
o Entire body of a tapeworm
o Consists of segments known as proglottids
o Segments form by budding from the posterior end of the
scolex
o Older mature segments move to the terminal end of the strobili as younger segments are produced
What are proglottids?
- segments of strobila of tapeworm
- Every mature proglottid contains both male and female reproductive organs (hermaphroditic)
- The reproductive organs mature gradually so that the proglottids toward the terminus contain fully developed reproductive organs and the uterus is filled with fertilized eggs.
Order and common name of
Hymenolepis nana
order: clyclophyllidea
common name: dwarf tapeworm
Order and common name of
Taenis saginata
order: clyclophyllidea
common name: beed tapeworm
Order and common name of
Taenia solim
order: clyclophyllidea
common name: pork tapeworm
Order and common name of
Echinococcus
order: clyclophyllidea
common name: dog tapeworm, hydatid tapeworm
Order and common name of
Diphyllobothrium latum
order: pseudophyllidea
common name: broadfish tapeworm
Disease-producing worm, its location in host and disease
dwarf tapeworm
hymenolepis nana
adults live in small instestine
light infections are asymptomatic; heavy worm burdens cause abdominal pain, diarrhea, headaches, dizziness
Disease-producing worm, its location in host and disease
beef tapeworm
taenia saginata
adults live in small instestine
most people are asymptomatic, can experience abdominal pain, diarrhea, and weight loss;
Disease-producing worm, its location in host and disease
pork tapeworm
taenia solium
adults live in small instestine
most people are asymptomatic, can experience abdominal pain, diarrhea, and weight loss;
Life cycle of intestinal cestodes
- adults in intestine
- embryonated eggs released from disintegrating gravid proglottids
- infective eggs in feces (diagnostic stage)
- egg infective when released (no intermediate host required) (infective stage)
- method of infection is that egg is eaten by human
- egg hatches in small intestine
- onchosphere invades intestinal villus
- cysticeroid larva forms
- emerges into lumen; scolen evaginates and attaches to mucosa
- matures completely
diagnostic stage of intestinal cestode
infective eggs in feces
infective stage of intestinal cestode
egg infective when released
How does autoreinfection happen with intestinal cestode
- embryonated eggs released from disintegrating gravid proglottids
- autoreinfection: egg hatches in GI tract
- the eggs then release the hexcanth embryo
- onchosphere invades intestical villus
Life cyle of H. nana
**Eggs of H. nana are immediately infective when passed with the stool and cannot survive more than 10 days in the external environment
- When eggs are ingested by an arthropod intermediate host (various sp. of beatles and fleas)
- They develop into cysticercoids, which can infect humans or rodents upon ingestion and develop into adults in the small intestine.
- When eggs are ingested (in contaminated food or water or from hands contaminated with feces), the oncospheres contained in the eggs are released
- The oncospheres (hexacanth larvae) penetrate the intestinal villi and develop into cysticercoid larvae
- Upon rupture of the villus, the cysticercoids return to the intestinal lumen, evaginate their scolices
- And attach to the intestinal mucosa and develop into adults that reside in the ileal portion of the small intestine producing gravid proglottids
- Eggs are passed in the stool when released from proglottids through its genital atrium or when proglottids disintegrate in the small intestine
Eggs of H. nana are (immediately/belatedly) infective when passed with the stool
Eggs of H. nana are immediately infective when passed with the stool and ca
Intermediate host of H. nana
arthropod intermediate host (various sp. of beatles and fleas)
What are cysticercoids?
Hatched embryonated egg in feces
which can infect humans or rodents upon ingestion and develop into adults in the small intestine
hexacanth embryo vs oncospheres (hexacanth larvae)
- internal autoinfection, where the eggs release their hexacanth embryo, which penetrates the villus continuing the infective cycle without passage through external environment
- When eggs are ingested (in contaminated food or water or from hands contaminated with feces), the oncospheres contained in the eggs are released
Life span of H. nana
4-6 weeks
Method of diagnosis of H. nana
- Recover and identify eggs in the feces
- The egg containing the oncosphere bear 3 pairs of hooklets and is surrounded by a membrane
- This membrane has 2 polar thickening from which arise
threadlike filaments extending into the space between the membrane and the shell
- Scolex is armed with one circlet of 5 hooks and 4 suckers, knob-like in shape
- The adult worm measures approx. 2.5-4cm
Major pathology and syptoms of H. nana
Disease name: Dwarf tapeworm infection
Light infection is asymptomatic
Heavy infection symptoms include intestinal enteritis,
abdominal pain, diarrhea, headache, dizziness, and anorexia
Multiple adults are commonly present
Treatment of H. nana
Niclosamide
Most prevalent human tapeworm found throughout US
H. nana
Life cycle of T. saginata and T. solium
- Eggs or gravid proglottids are passed with feces; eggs
can survive for days to months in the environment - Cattle and pigs become infected by ingesting vegetation contaminated with eggs or gravid
proglottids - In the animal’s intestine, the oncospheres hatch, invade the intestinal wall and migrate to the striated muscle, where they develop into cystecerci. A cystecercus can survive for several years in the animal.
- Humans become infected by ingesting raw or undercooked infected meat.
- In the intestine, the cysticercus develops after 2 months into an adult tapeworm which can survive for years. The adult tapeworm attach to the small intestine by their scolex and reside in the small intestine
- The adults produce proglottids which mature become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approx. 6 per day)
What is Taeniasis?
Taeniasis is the infection of human with adult tapeworm of T. saginata and T. solium
Humans are (the only/one of) definitive hosts of T. saginata and T. solium
Humans are the onlydefinitive hosts of T. saginata and T. solium
Infective stage of Taeniasis
Infective Stage: Oncosphere develops to cysticercus larva in tissue of cow or pig
Diagnostic stage of Taeniasis
Diagnostic Stage: Free eggs or gravid proglottids passed in feces
Which is the correct pairing
a. cysticercoids, cysticercus larva = taenia saginata/soium
b. cysticercoids, hexacanth larvae = H. nana
cystecercus, cysticercus larva = taenia saginata/soium
d. cystecercus, hexacanth larvae = H. nana
b. cysticercoids, hexacanth larvae = H. nana
c. cystecercus, cysticercus larva = taenia saginata/soium
Methods of diagnosis for taeniasis
- Recover egg or gravid proglottid (or scolex after drug treatment) in feces
- Proglottid and scolex identification
o Eggs of the two species are identical
T. saginata vs. T. solium
o T. saginata: has 15 to 30 lateral uterine branches in
each side of the gravid proglottid and a scolex with
only 4 suckers, smooth – no rostellum
o T. solium: has 7 to 12 lateral uterine branches on each
side of gravid proglottid and the scolex has 4 suckers plus a central crown of hooks (the “armed” tapeworm), rostellum with hooks (double crown)
Which has rostellum:
H. nana
T. saginata
T. solium
T. solium
4 suckers, rostellum with hooks (double crown)
Major pathology of
T. saginata
T. solium
- Most infected people are asymptomatic
- Abdominal pain, diarrhea and weight loss can occur
- Eosinophilia is moderate
Disease names:
T. saginata
T. saginata : taeniasis, beef
tapeworm infection
Disease names:
T. solium
T. solium: taeniasis, pork tapeworm infection; cystecercosis (larval infection in tissue)
What happens to T. solium when ingested by humans?
- Humans can serve as accidental intermediate hosts for T. solium.
- If eggs of T. solium are accidentally ingested or released from a proglottid in the intestinal tract, the eggs can hatch in the intestine and the larvae will migrate to form cysticercus bladders in any organ or nervous tissue (cycticercosis; neurocysticercosis)
- Neurocysticercosis can cause obstructive hydrocephalus (symptoms include epilepsy, headache, papilledema and vomiting)
- Can be fatal if racemose develops in the brain
Treatment for adult tapeworm:
Praziquantel or Niclosamide
Treatment for cysticercosis:
Albendazole or Praziquantel,
Anticonvulsants for seizures, corticosteroids for Neurocysticercosis symptoms, surgery
Common name of Diphyllobotrium latum
(Broadfish Tapeworm)
Life cycle of (Broadfish Tapeworm)
- adults in small intestine
- diagnostic stage: undeveloped egg passed in feces
- coracidium develops and larva hatches
- a copepod (1st intermediate host) eats larva
- develops to a proceroid larva
- fresh water fish (2nd intermediate host) eats copepod
- proceroid larva digested; penetrates mucosa and moves to muscles in fish
- infective stage: proceroid to pleurocercoid in fish muscle
- method of infection: pleurocercoid ingested by human in freshwater fish
- scolex of pleurocercoid attaches to mucosa
- matures
Diagnostic stage of Diphyllobotrium latum
- diagnostic stage: undeveloped egg passed in feces
- Evacuated proglottids usually in chains ranging from a few inches to several feet (Adult worms can reach upto 10 meters or more in length and may contain 3000 proglottis. Scolex is spatulated with no rostellum or hooklets.)
- Scolices are also diagnostic but are rarely evacuated intact
Infective stage of Diphyllobotrium latum
- infective stage: proceroid to pleurocercoid in fish muscle
Method of infection of Diphyllobotrium latum
- method of infection: pleurocercoid ingested by human in freshwater fish
Major Pathology and symptoms of Diphyllobotrium latum
- Symptoms include intestinal obstruction (adult can grow to 20 meters) and abdominal pain
- Weight loss and weakness
- In about 1% (usually of Scandinavian descent), anemia (macrocytic type) and eventual nervous system disturbances results from a deficiency caused by tapeworm’s utilization of 100% dietary B12
- A human can develop tissue plerocercoid in a copepod is accidentally ingested.
Disease names of Diphyllobotrium latum
Diphyllobotriasis, Dibothriocephalus anemia, fish tapeworm infection, Broadfish tapeworm infection
Treatment of Diphyllobotrium latum
- Niclosamide or Praziquantel
- Distribution: in temperate regions where freshwater fish are a common part of the diet or raw fish are eaten.
o In Europe, estimates up to 20% of the Finnish people
and up to 100% of residents of Baltic region.
Common name of Echinococcus granulosus
(Hydatid Tapeworm)
Life Cycle of Echinococcus granulosus
- adults live in intestine of dogs or other wild canines (definitive host)
- eggs in feces (resemble Taenia eggs)
- method of infection: human (accidental intermediate host) ingests eggs by close contact with infected dog, sheep or other herbivore (intermediate host) ingests eggs from pasture contaminated with dog feces
- hexacanth embryo migrates to tissue, develops into hydatid cyst
- diagnostic stage: hydatid cyst in liver, lung, or other organs
- viscera of infected herbivore eaten by canine
- cyst digested in the canine intestine, and each scolex in the cyst develops to an adult tapeworm
Methods of diagnosis of Echinococcus granulosus
- Serologic tests: indirect hemmagglutination, ELISA
- Presence of Scolices, brood capsules, hyatid sand, or daughter cysts in the hyatid cyst fluid as detected by biopsy (not recommended because leakage of cyst fluid can cause
anaphylaxis)
- X-ray examination, ultrasound scan, or CT detection of cyst mass in organ, especially if calcified.
Major Pathology of Echinococcus granulosus
- Symptoms vary according to location and size of cyst
- Expanding cysts causes pressure necrosis of surrounding tissues
- Cyst growth or rupture can result in death
- Anaphylactic shock may occur if the cyst ruptures
- Other findings include eosinophilia, urticarial and bronchospasm
- In the liver (most common site) – no symptoms develop until the cyst gets large (nearly a year after ingestion of egg); then jaundice or portal hypertension develops
- In the lung – no symptoms until the cyst becomes large; then coughing, shortness of breath, and chest pain develop
- In other sites, symptoms are related to enlarging cyst pressure
Treatment of Echinococcus granulosus
Treatment: SURGERY; MEBENDAZOLE OR ALBENDAZOLE
Distribution of Echinococcus granulosus
- Distribution: Human infections occur as zoonoses primarily in sheep- raising areas where domestic dogs are used in herding
o Echinococcus cysts in sheep or human tissues produce daughter cysts and brood capsules, all lined with
germinal tissue that buds off many protoscolices
o Each protoscolex can form the scolex of an adult if
ingested by a canine.
