dicrocoelium dendriticum by carolynn peter & ryan hamm
TRANSCRIPT
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