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Dicrocoelium dendriticum

Dicrocoelium dendriticum is a small fluke that inhabits the bile ducts of a variety of mammalian hosts. It has a complex life cycle involving three hosts: land snails as the first intermediate host, ants as the second intermediate host, and various grazing mammals as the definitive host. D. dendriticum alters the behavior of infected ants, causing them to cling to plant tops at night where they are more likely to be eaten by grazing mammals. While it typically does not cause severe effects in hosts, heavy infections can lead to liver damage and other issues. Diagnosis is challenging as the eggs are small and difficult to detect in feces. No single treatment has proven fully effective against the parasite.

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Dicrocoelium dendriticum Www.RCVetS.com
Dicrocoelium dendriticum • Kingdom: Animalia • Phylum: Platyhelminthes • Class: Trematoda • Order: Plagiorchiida • Family: Dicrocoeliidae • Genus: Dicrocoelium • Species: D. dendriticum • Small flukes which inhabit the bile ducts of a wide variety of mammals Dicrocoelium dendriticum • Small flukes which inhabit the bile ducts of a wide variety of mammals
Dicrocoelium dendriticum • Geographical Distribution: – North/Central/South America – Europe – Asia – North/Central Africa *Favors Dry Conditions* • Definitive Host: – Domestic and wild cattle, sheep, goats – Humans • Intermediate Host: – 1st : Land snail (Cionella lubrica) – 2nd : Ant (Formica fusca)
Pop Quiz #1 1. Name one country this particular parasite is found. (North/Central/South America, Europe, Asia, or North/Central Africa) 2. Name two definitive hosts for this parasite. (Cattle, sheep, goats, or humans)
Morphology • Adult: 6-10mm by 1.5-2.5mm • Egg: 36-45µm by 22-30µm
Life Cycle
Life Cycle a.) Adult b.) Egg c.) Miracidium d.) Daughter sporocyst e.) Mature Cercariae f.) slime-balls g-h.) transformation to metacercariae
Life within the Snail • Eggs released in definitive host’s feces • Snail eats • Miracidium hatches from egg in intestine and penetrates gut wall • Transformation to mother sporocyst • Produce 1st and 2nd generation daughter sporocysts with cercariae through asexual reproduction • Cercariae accumulate • Cercariae escape through snail’s slimeballs
Life within the Ant • Ant eats the cercariae-containing slime ball • Transform to metacercariae which encyst – Most remain in the hemocoel – 1 or 2 migrate to subesophageal ganglion, “brainworms” (these are not infective) • Alter ant’s behavior – When temperatures drop in the evening ants climb to the tops of grasses/plants. – Mandible muscles spasm and lock onto the plant – Remain there till they are either eaten or the temperature warms and they resume normal behavior
Life within the Definitive Host • Infected ant is eaten by the host • D. Dendriticum excysts in the duodenum • Migrates upstream to the common bile duct and then the liver • Flukes mature in about 6 or 7 weeks • Reproduce by hermaphroditism or cross insemination • Eggs are produced and released in feces
Pop Quiz #2 1. What is the order the intermediate hosts come into play in this parasite’s life cycle? (First the snail, then the ant) 2. What makes this parasite unique? (It alters the behavior of the ant)
Pathogenesis/Clinical Signs • If present in small numbers, parasite does not have much affect on host • In severe cases when parasite is present in large numbers, following symptoms may occur: – Cirrhosis of liver (leading to decreased function) – Anemia – Edema – Emaciation • Appears to be no immunity
Diagnosis • Fecal floatation is one way to diagnose whether or not the parasite is present; however, the eggs are very small and not readily identified because they do not float well • Usually found at slaughter (find adults in liver)
Treatment • Products: – Valbazen – Thiabendazole – Triclabendazole – Albendazole – humans – Praziquantel – not in food animals • No treatment has been proven effective
Prevention/Control • Treat all animals exposed to infection (two or three times a year) • Control Intermediate Hosts – Calcium cyanamide molluscicide and chemical fertilizers • High costs • Ecological effects – Introduce turkeys, chickens or ducks to eat snails/ants – Cover ant nests with tree branches • Infected ants are generally found within 30 to 50 cm from their nest.
Prevention/Control • As humans we should avoid the urge to nibble or suck on grass which may have ants on it.
Public Health Concerns • Unless severe liver changes occur; infected animal is still edible • Humans have been infected but it is very rare • Economic losses seem less in D. dendriticum than in other flukes • Reports of Dicrocoeliosis have increased worldwide in the past 20 years
Pop Quiz #3 1. Why is a fecal floatation not the best way to diagnose this parasite? (The eggs are small and do not float very well) 2. There is only one drug that is effective in getting rid of this parasite. True or False? (False – no drug has been proven effective)
References • Associate Database. Dicrocoeliosis. Article obtained February, 12, 2007. http://www.vin.com/Members/Associate/Associate.plx?DiseaseId=1499 • Dicrocoelium dendriticum – The Lancet Fluke. Dr. Chrissy O’Neill’s notes • Peacock, Dr. Andrew. Dicrocoelium dendriticum – The Lancet Fluke of Sheep. Published by Newfoundland and Labrodor Agriculture on April 14, 2004. Article obtained February 12, 2007. http://www.nr.gov.nl.ca/agric/animal_diseases/domestic/pdf/dicro.pdf • Wikipedia. Dicrocoelium dendriticum. Obtained February 12, 2007. http://en.wikipedia.org/wiki/Dicrocoelium_dendriticum • Otranto, D., & Traversa, D. (2002/8/22). A review of dicrocoeliosis of ruminants including recent advances in the diagnosis and treatment. Veterinary Parasitology, 107(4), 317- 335. • Otranto, D., & Traversa, D. (2003/1). Dicrocoeliosis of ruminants: A little known fluke disease. Trends in Parasitology, 19(1), 12-15. • Schmidt, G., & Roberts, L. (2005). Foundations of Parasitology (7th ed.). New York, NY: McGraw-Hill.