Dicrocoelium dendriticum

By Carolynn Peter & Ryan Hamm

Classification

Kingdom AnimaliaPhylum Platyhelminthes

Class TrematodaOrder Plagiorchiida

Family DicrocoeliidaeGenus Dicrocoelium

Species dendriticum

Background

Family Dicrocoeliidae use land snails as first intermediate host

Known as the “lancet fluke” or “small liver fluke”

Causes the disease dicrocoellosis

Favors dry conditions

Human infection is rare, but can occur

Morphology

6 to 10 mm long by 1.5 to 2.5 mm wide

Widest near the middle

Body is pointed at both ends

Lobate testes lie directly behind acetabulum

Loops of the uterus fill most of the body behind ovary

Hosts

Definitive Host: Ruminants are the usual

definitive hosts Sheep, cattle, goats, deer

Accidental Host: other herbivorous

animals, carnivores, and humans can serve as a host

Intermediate Host: Land snail (Cionella

lubrica) An ant (Formica fusca)

Geographic Range

Found in: Most of Europe

and Asia North America Australia Northern Africa

Life Stages

Miracidium- first larval stage of a digenetic trematode

Mother sporocyst- asexual stage of development that forms more sporocysts

Cercariae- Juvenile digenetic trematode, produced by asexual reproduction within a sporocyst

Metacercariae- stage between cercaria and adult in the life cycle of most digenetic trematodes D. dendriticum egg containing a miracidium.

Life Cycle

http://www.youtube.com/watch?v=lGSUU3E9ZoM

Life Cycle in the Land Snail (1st intermediate host)

Adult flukes live in the bile ducts within the liver.

Eggs leave the liver and are passed with the feces.

The eggs contain a miracidia.

A land snail must eat the egg before it will hatch.

In the small intestine of the snail, the egg hatches and releases miracidia

The miracidia penetrates the gut wall and develops into a mother sporocyst in the digestive gland.

Mother sporocysts produce daughter sporocysts which produce cercariae .

Three months after infection the cercariae accumulate in the “lung” (mantle cavity) of the snail or on its body surface which causes the snail to produce thick mucus.

The mucous surrounds the cercariae and expels the cercariae in the slime ball as it crawls along.

Life Cycle in the Ant (2nd intermediate host)

Fluke development continues when the cercariae are eaten by the second definitive host an ant.

An ant will eat the slime ball and the cercariae become metacercariae

Most of the metacercariae (infective to definitive host) will encyst in the spaces between the organs of the ant where the blood circulates (hemocoel).

Some metacercariae migrate to the subesophageal ganglion of the ant and encyst there These metacercariae (not infective to definitive host) are called

“Brainworms” and will change the behavior of the ant.

In the evening the ants will crawl to the tops of grasses and other plants and hang from it's mandibles. When the temperature warms up the ant returns to normal

behavior.

On the grass and other plants the ant is susceptible to the definitive host during grazing.

Life Cycle in Definitive Host

Once eaten by a definitive host the metacercariae excysts in the duodenum.

It will migrate upstream to the bile ducts since it is attracted to bile and into the liver, mature and produce eggs.

Flukes mature in 6 to 7 weeks

Flukes reproduce by hermaphroditism

Eggs are produced and released in feces of definitive host

Symptoms

No trauma to the gut wall or liver parenchyma resulting from migrating juveniles

Biliary dysfunction

Bile duct inflammation

Fibrosis

Hepatocyte damage

Anemia

Edema

Emaciation

Diagnosis

Traditionally eggs of D. dendriticum are found in feces of infected animals

Post-mortem examination of liver

ELISA using D. dendriticum antigen can catch the disease early on

Treatment

Praziquantel

Benzimidazoles Albenzole Fenbenazole Mebendazole

Control

Animal husbandry practices Do not allow

ruminants to graze in the early morning or at night

Try and control the intermediate hosts Use chickens,

geese or ducks

Quiz Time

1. What are the two intermediate hosts? A. Land Snail and an Ant

2. What is the geographic range of D. dendriticum?A. Most of Europe and Asia, North America, Australia, Northern Africa

3. Who are the accidental host?A. Other herbivorous animals, carnivores, and humans

4. What life stage is a juvenile digenetic trematode?A. cercariae

5. During the evening and morning hours, what unusual behavior does the ant display?

A. Ants climb and cling to top of grass at night or early morning

6. How is D. dendriticum diagnosed?A. Fecal exam for eggs, autopsy of liver, ELISA

References

Janovy, John Jr. and Roberts, Larry S., Foundations of Parasitiology, 8th Edition, 2009

http://en.citizendium.org/wiki/Dicrocoelium_dendriticum

http://www.cdfound.to.it/html/dicro.htm

www.dpd.cdc.gov/dpdx/html/imagelibrary/Dicrocoeliasis_il.htm

www.suite101.com/content/dicrocoelium-dendriticum-a35177

http://www.peteducation.com/article.cfm?c=2+2107+2255&aid=731