Trematodes

Question 1

General structure of trematodes?

Answer 1

• Flukes
• leaf-like body
• Flattened
• a gut is present

Question 2

What do trematodes in general feed on? (3)

Answer 2

• blood
• tissues
• intestinal content

Question 3

trematode general life cycle?

Answer 3

• eggs in feaces
• snail intermediate host
• metacercaria encysts
• ingestion by definite host

Question 4

location of trematode parasitism?

Answer 4

• intestinal parasites

- tissue organs

Question 5

Usual trematode intermediate host?

Answer 5

Snail

Question 6

what is a miracidium?

Answer 6

a free-swimming ciliated larval stage in which a parasitic fluke passes from the egg to its first host, typically a snai

Question 7

Trematode egg features? (3)

Answer 7

• operculum present (a trap door at one end)
• hatching occurs in the water, which realises miracidium
• has specific behaviours which lead to snail host

Question 8

explain “focal distribution”

Answer 8

• parasites exhibit a focal distribution, that is, they tend to cluster geographically or among certain population strata.

Question 9

what is the most important factor influencing trematode distribution? list 3 other major factors for transmission.

Answer 9

• most important = snail intermediate host distribution

Other factors

• presence of suitable secondary intermediate host (in Australia = plants)
• final host feeding behaviours
• climate

Question 10

where to find trematodes of veterinary importance?

Answer 10

“food-borne” - aquatic plants

Rarely- ingestion of native fauna

Question 11

What are the two liver fluke scientific names? what are the host species? Adult location in host? Amount of Flukes to cause economic damage?

Answer 11

• F.hepatica F. gigantica ( both species hybrid and/or introgressed)
• sheep and cattle
• large leaf-shaped flukes
• Adults in bile duct - blood
• 30-40 flukes per cattle or sheep

Question 12

Fasciola hepatica life cycle? (12)

Answer 12

• metacercaria ingested along watercress by ruminant or humans
• metacercaria hatches in small intestine
• larva penetrates small intestines
• larva enter livers
• adults live in bile ducts and liver tissue
• eggs laid and pass into small intestines
• eggs leave host in feaces
• eggs incubate
• eggs hatch in fresh water
• miracidium enters snail
• cercaria leaves snail
• cercaria encysts on watercress, now a metacercaria

Question 13

disease and pathology of liver flukes during host invasion (3) acute and the chronic disease?

Answer 13

Host invasion

• Acute (liver rot) when juveniles invading liver
• black disease
• secondary liver infection (clostridium noryi)

Chronic disease

• anaemia
• enlargement of liver
• enlargement of bile duct
• “bottle jaw”

Question 14

effectiveness of liver fluke anthelminthics (triclabendazole)?

Answer 14

liver fluke is resistant to it in some regions

Question 15

Host immunity to liver flukes? (2)

Answer 15

• Sheep do not acquired resistance at any age

- Cattle have severe disease as calves then acquire resistance

Question 16

what are paramphistomes?

Answer 16

• Stomach flukes

Question 17

Paramphistomes intermediate host?

Answer 17

• Planorbid snail

Question 18

paramphistomes life cycle?

Answer 18

• metacercaria encrypt on vegetation
• after ingestion immature flukes move to intestine
• migrate to rumen and reticulum
• prepatency of 7-13 weeks

Question 19

prevalence and usually severity of paramphistomes

Answer 19

• most stock carry light infection
• adults not associated with disease
• heavy infection with immature flukes may be associated with disease: damage to intestine appetite loss, diarrhoea etc

Question 20

Schistosome prevalence

Answer 20

• endemic in 74 developing countries with more than 80% infected people living in sub-saharan Africa
• 206 million people infected
• 100,000s of deaths a year
• important zoonoses

Question 21

Schistosomes life cycle

Answer 21

• in fresh water Cercariae
• cercaria penetrate skin
• in host become schistosomula
• –>veins, heart, lungs, heart, arteries, liver, hepatic portal vein
• main and female mate
• go to mesenteric vessels of bowels
• egg laying
• eggs retained in host tissues (causing disease)
• eggs excreted in feaces
• ovum in fresh water
• become miracidum
• enters oncometeria snail
• on developed in cercariae leave snail

Question 22

where are trematodes in SE Asia ingested by people?

Answer 22

• Fish borne trematodes
• approx 60 species- most are intestinal flukes
• but also liver and lung fluke

Question 23

cholangiocarcinoma

Answer 23

a type of cancer that forms in the slender tubes (bile ducts) that carry the digestive fluid bile.

Question 24

what are Opisthorchis and clonorchis? what disease can they cause?

Answer 24

• Human liver flukes

- opisthorchis + diet may lead to cancer of bile duct - cholangiocarconoma