Common Cestode Infections (Franco Falcone)

Question 1

What is Taenia solium?

Answer 1

Pig tapeworn

Question 2

What is Taenia saginata?

Answer 2

Beef tapeworm

Question 3

What are cestodes?

Answer 3

Segmented flatworms

Question 4

What definitive hosts are there for T. solium, saginata or asciatica?

Answer 4

Humans

Question 5

How does infection by solium, saginata or asciatica occur?

Answer 5

Ingestion of raw or undercooked meat

Question 6

Where do adult cestose worms reside in human hosts?

Answer 6

Small intestine, attached via their scolex.

Question 7

What is Echinococcus granulosus?

Answer 7

Hydatid tapeworm

Question 8

What is Echinoccus mutlilocularis?

Answer 8

Small fox tapeworm

Question 9

What is the Taenia species life cycle?

Answer 9

Eggs or gravid proglottids in faeces are passed into the environment.
Cattle (T. saginata) or pigs (T. solium) become infected by ingesting vegetation contaminated with eggs or gravid proglottids.
Oncospheres hatch, penetrate intestinal wall and criculate to the musculature; the oncospheres develop into cysticerci in muscle.
Humans are infected by ingesting raw or undercooked meat that is infected. = TAENIASIS
The scolex attaches to the intestine and adults grow in small intestine.

Question 10

What symptoms are associated with Taeniasis?

Answer 10

Obstruction, diarrhoea, hunger pains, weight loss or appendicitis (reported rarely).
Most common complaint is discomfort and or embarrassment caused by the proglottids crawling from the anus.

Question 11

What is the difference between Taeniasis and Cysticercosis?

Answer 11

In cysticercosis, humans become the pig and ingest eggs or gravid proglottids. Once embyronated eggs are ingested by humans, the oncospheres hatch and can then penetrate the intestinal wall and circulate to musculature where the cystercerci develop / mature.

Question 12

How are oncospheres activated?

Answer 12

GI secretions release the infective larvae

Question 13

How do oncospheres cause disease?

Answer 13

They cross the gut wall and can end up anywhere in the body, where they undergo further maturation to cysticerci.
Cysticerci are mainly found in the CNS and eyes, more rarely in subcut or muscle tissue.
Neurocysticercosis - brain of swiss cheese.
CNS or ocular disease causes serious problems e.g. seizures or intracranial hypertension.

Question 14

What drugs can be used as Taeniacides?

Answer 14

Praziquantel or Niclosamide (inhibits glucose uptake)

Both are unlicensed in the UK but can be made on special order.

Question 15

What is Praziquantel?

Answer 15

Unlicensed in UK but made as specials
Prescribed on a named patient basis
Oral chewable tablets (single dose)
PZQ treatment means the tapeworm can no longer resits digestion.

Question 16

What is Niclosamide?

Answer 16

Also unlicensed in the UK but made as a special
Prescribed on a named patient basis, also a single dose of oral chewable tablet
Not effective against pinworms or roundworms
Works by inhibiting glucose uptake and oxidative phosphorylation
Cheap and effective but second choice to PZQ because numerous side effects

Question 17

What are zoonotic infections?

Answer 17

Occurs when a pathogen is usually found in animals occasionally infects humans

Question 18

What makes zoonotic infection problematic?

Answer 18

Animal reservoir so hard to eradicate
Pathology often more severe that human parasites
Can be transmitted by pets or livestock

Question 19

What examples are there of zoonotic infections?

Answer 19

Echinococcus species
E. granulosus - cystic echinococcus (hydatid)
E. multilocularis - alveolar echinococcus (small fox) - very difficult to treat.

Question 20

What is the life cycle of Echinococcus species?

Answer 20

Adult worms in the small intestine of the definitive host (cat, dog, wolf, dingo)
Embryonated eggs in faeces
Sheep (intermediate host) ingests the eggs; the egg hatches in the small bowel and releases an oncosphere That penetrates the intestinal wall and migrates through the circulatory system into various organs, especially the liver and lungs. In these organs, the oncosphere develops into a cyst that enlarges gradually, producing protoscolices and daughter cysts that fill the cyst interior.
The intermediate host dies or is hunted and eaten by the definitive host; infected by ingesting the cyst-containing organs of the infected intermediate host. After ingestion, the protoscolices. If we ingest the meat of an infected intermediate host then we become the sheep and cysts migrate to the eyes, liver and brain etc.

Question 21

What is cystic echinococcosis?

Answer 21

It is caused by E. granulosa and may be without symptoms for years due to its slow growth.
Symptoms depend on the size and sometimes causes relatively non-specific symptoms i.e. cough, abdo pain and discomfort. Rupture of cysts (e.g. during surgical removal) can cause allergic reaction and death by anaphylaxis.

Question 22

What is alveolar echinococcosis?

Answer 22

It is caused by E. multilocularis
Asymptomatic incubation of 5-15 years
Larvae do not fully mature to cysts in humans but form vesicles which invade and destroy neighboring tissues
Growth is similar to metastatic cancer, clinical signs include weight loss, abdominal pain, general malaise, signs of hepatic failure.

Question 23

How can Echinococcus species be transmitted?

Answer 23

Dogs can be infected by eating the liver of infected sheep. Tapeworm eggs can then be found in the dogs stool. Human infection only occurs by faecal-oral route leading to the ingestion of eggs, e.g. directly by intimate handling of the pet (fur may contain eggs) but also contaminated soil or veg.
The eggs can survive snow and freezing conditions

Question 24

What factors affect the pathology of Echinococcosis?

Answer 24

Size, quantity and location of the cysts (neurology for example)
Cysts can grow to a large size without causing symptoms but small cysts in the wrong location can cause severe symptoms

Question 25

How can infection with Echinococcus be diagnosed?

Answer 25

Ultrasounds, CT and MRI can confirm diagnosis of specific infection i.e. cystic or alveolar.
Serological tests
No egg detection in faeces.

Question 26

What treatment options are there for cystic echinococcus?

Answer 26

Percutaneous treatment of the hydatid cysts according to the PAIR minimal invasive technique - injection of a protoscolicide agent
Surgery
Anti-infective drug treatment
Watch and wait

Question 27

What treatment options are there for alveolar echinococcus?

Answer 27

Early diagnosis and radical tumour-like surgery followed by anti-infective prophylaxis with albendazole.