Cestodes of the Intestinal Tract

Apart of the Helminth GI Infection Notes

What are the cestodes of the intestinal tract we went over?

• Dibothriocephalus latus (Diphyllobothrium latum)

• Dipylidium canium

• Hymenolepis nana

• Taenia spp.

Epidemiology of Dibothriocephalus latus/Diphyllobothrium latum

• worldwide temperate regions (cool lake regions), in which freshwater fish are eaten raw or insufficiently cooked

  • in the early 1970s, ~9 million infected worldwide (5 million in Europe, 4 million in Asia and some in Americas)

• Animal reservoirs: bears, walruses, members of the canine and feline families, and birds

Life Cycle of Diphyllobothriid

• infection occurs upon consumption of plerocercoids larvae in undercooked fish (infective stage)

• larvae development into adults in the small intestine

• adults shed eggs in the stool (diagnostic stage)

• eggs in the water develop into coracidia (exit through operculum) which are ingested by crustacean (first intermediate host)

• coracidia develop into larvae crustacean is consumed by fish (second intermediate host)

• larvae migrate to deeper tissue of fish

Infective stage and diagnostic stage of Diphyllothriid

• infective stage: plerocercoids larvae in undercooked fish

• diagnostic stage: eggs in the stool

First and second intermediate host for Diphyllothriid

• first intermediate host: crustacean

• second intermediate host: fish

Clinical Syndrome of Dibothriocephalus latus/Diphyllobothrium latum

• mostly asymptomatic

• abdominal pain, nausea, vomit, weight loss

• 40% with low serum levels of vitamin B12

Diagnosis of Dibothriocephalus latus/Diphyllobothrium latum

• stool examination reveals the bile-stained operculated egg with its known at the bottom of the shell

• typical proglottids with the rosette uterine structure may also be found in stool specimens

Treatment and prevention of Dibothriocephalus latus/Diphyllobothrium latum

• praziquantel (does not guarantee the removal of the scolex - attached to the intestines)

• vitamin B12 supplements, as needed

• avoid consumption of insufficiently cooked fish or may freeze the fish (-20C for 7 days) prior to consumption

Epidemiology of Diphylidium canium

• most common tapeworm of dogs and cats worldwide (usually asymptomatic)

• no good evidence of prevalence, but the consensus is that it is high

• occasionally found in humans, espcecially children

Life Cycle of Dipylidium

• infection occurs upon consumption of cysticercoid larvae in flea (infective stage)

• in the small intestine of the host, the cysticercoid develops into an adult

• as proglottids mature, they detach from the adult and are shed in the stool (diagnostic stage)

• in the environment, the proglottids disintegrate and release egg packets

• the flea (intermediate host) ingests the egg packets

• oncosphere within the eggs are released into the flea’s intestine which develops into a cysticercoid

Clinical Syndromes of Dipylidium canium

• light infections are asymptomatic (rear end itching)

• heavy infections produce abdominal discomfort and diarrhea

• maybe self-limiting, with spontaneous cure

Diagnosis of Dipylidum canium

• stool examination reveals colorless egg packets

• proglottids may be in feces brought to physicians by patients

Infective stage and diagnostic stage for Dipylidum

• infective stage: Consumption cysticercoid larvae in flea

• diagnostic stage: proglottids

Intermediate host for Dipylidium

flea

Treatment and prevention of Dipylidium canium

• praziquantel

• dogs and cats

  • remove fleas

  • deworm

• avoid getting licked by animals

Epidemiology of Hymenolepis nana

• worldwide distribution (most common cestode infection)

• affects millions of people, primarily children (50 to 75 million) (poor sanitation/personal hygiene)

  • highest in Sicily (46%), Argentina (34%), and Soviet Union (26%)

  • in the US, mostly found in Southeast (and among institutionalized children) or internationally adopted children

• animal reservoir: rodents

Life Cycle of H. nana

• infection occurs upon consumption of eggs or cysticercoid larvae in arthropod (infective stage) in contaminated water/food/hands

• oncospheres are released in the intestines and develop into cysticercoid larvae

• larvae develop into adults in the small intestine; adult produces eggs that are passed in the stool (diagnostic stage)

• eggs in the environment are ingested by an arthropod (intermediate host - beetle or flea)

• eggs develop into cysticercoid larvae

• and alternative mode of infection - autoinfection (eggs hatch in the intestines) (can persist for years) (also means person to person transmission)

Clinical Syndromes of Hymenolepis nana

• light infections are asymptomatic

• heavy infections produce diarrhea, abdominal pain, headache, anal itching, anorexia

Diagnosis of Hymenolepis nana

stool examination reveals the characteristic H. nana egg with its six-hooked embryo and polar filaments (proglottids disintergrate)

Treatment and prevention of Hymenolepis nana

• praziquantel (supportive care is usually sufficient)

• education and improved sanitation

Infective stage and diagnostic stage of H. nana

• infective: Consumption of egg or cysticercoid larvae in arthropod

• diagnostic: eggs

Intermediate host of H. nana

beetle or flea

Name and differentiate the two tapeworms

• Taenia solium (pork)

• Taenia saginata (beef)

• examination of the proglottids

Epidemiology of Taenia

• worldwide distribution

• ~50 million people are infected

  • highest prevalence in central Asia, the near east, and central and eastern Africa

  • ~1000 cases of cysticercosis annually in the US (most in immigrants from Latin America)

  • Human and animal reservoirs: T. solium - pig; T. saginata - cow

Life Cycle of Taenia

• infection occurs upon consumption of raw/undercooked meat containing cysticercoid larvae (infective stage)

• in the small intestines, the larvae develop into the adult

• adult produces eggs that are passed in the stool (diagnostic stage) or proglottids detach from the adult and are passed in the stool

• eggs/proglottids are in the environment are ingested by the intermediate host (either the cow - T. saginata or pig - T. solium)

• oncospheres hatch from the eggs and migrate to the striated muscles where they develop into cysticercoid larvae

Infective stage and diagnostic stage of Taenia

• infective stage: Consumption of meat containing cysticercoid

• diagnostic stage: eggs or proglottids

Cysticercosis Transmission

• humans are definitive hosts

• consumption of water or vegetation contaminated with T. solium eggs from human feces

• autoinfection may occur when eggs from a person infected with the adult worm are transferred from the perianal area to the mouth on contaminated fingers

Clinical Syndromes of Taenia

• most are asymptomatic; abdominal discomfort, diarrhea and weight loss can occur

• Cysticercosis (T. solium larvae) in muscle/connective tissue, neurocysticerosis (60%), lungs, and eyes (common in Mexico and Central America)

Diagnosis of Taenia

• stool examination may reveal proglottids and eggs

• eggs of T. saginata and T. solium are identical so eggs alone are not sufficient for species identification

• examination of the proglottids to differentiate the 2 species

Treatment and prevention of Taenia

• praziquantel (surgery may be needed for removal of cysts)

• education and sanitation

• cook meat to safe temperatures

  • pork: 145 F

  • beef 160 F

• improved meat inspection