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Medical Helminthology: Flatworms—human parasites

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1 Medical Helminthology: Flatworms—human parasites
Lecturer: ass. prof. Tetyana Bihunyak

2 According to the way of development helminths are classificated into biohelminthes and geohelminthes. Geohelminthes develop without intermediate host. Soil is the best environment for their egg's development. Humans are infected through dirty fruits and vegetables, which contain geohelminthe's eggs (Ascaris lumbricoideus). Biohelminthes have complete life cycle with definitive and intermediate hosts. There are trophycal connections between definitive and intermediate hosts (for example, Taenia solium).

3 General characteristic of Flatworms (Phylum Plathelminthes)
The flatworms consists of 12, 200 species, including classes of parasitic worms: Trematoda, Cestoda All flatworms are acoelomate, triploblastic, bilaterally symmetrical; flattened dorsoventrally They have a definite head at the anterior end Their bodies are solid: the only internal space consists of the digestive cavity. They have no anus; a single opening to the digestive system serves as both mouth and anus Wastes probably move out of flatworms mostly by diffusing across the general body surface The most of flatworm species are hermaphrodites.

4 General characteristic of Class Trematoda
1)  Flattened dorsoventrally (leaf-like). 2)  Unsegmented. 3)  Body is covered by cuticle. 4)  Organs of fixation: oral sucker, ventral sucker. 5) Organs and systems: digestive system, excretory system, nervous system. Genital system: Trematodes are hermaphrodites except genus Schistosoma. 6) The life cycle is passed in two hosts (alternation of hosts) and has sexual and asexual stages.

5 Schistosomiasis is second only to malaria in human impact among tropical diseases and is the third most prevalent parasitic disease in the world.


7 Schistosomiasis/Distribution
Schistosoma haematobium, S. mansoni infections: in sub-Saharan Africa S. mansoni remains endemic in parts of Brazil, Venezuela and the Caribbean S. japonicum still occurs in China, Indonesia & the Philippines

Schistosoma mansoni and Schistosoma japonicum cause Hepatosplenic Schistosomiasis. Schistosoma haematobium causes Urinary Schistosomiasis. Localization: venous vessels of bowel, liver, and bladder. Morphology: atypical trematodes which the adult female nesting within a specialized groove in the body of the larger male.

9 Schistosome adult worms
Male/female pair copulate throughout life-produce eggs Females resides in canal-Important for maturation Some differences among species Worm pairs can live for more than 10 years in a host Pair migrate back against the blood flow to the mesenteries around the intestine.

10 BLOOD FLUKES Infective stage for human: cercariae.
Definitive host: man. Intermediate host: snail. Mode of transmission: penetration of skin by cercarie.

11 Cercaria in the water It is composed of a body 125 m long by 25 m in diameter to which a 200 m long tail is attached. First escape into the hemolynph and then through the snail’s integument Swim into the surrounding water to find their definitive host Swims by alternating side-to-side rhythmic contractions

12 In a canal off the Nile, just southwest of Cairo, Egypt
How do you get schistosomiasis ??? How about total body immersion …. In a canal off the Nile, just southwest of Cairo, Egypt In a storage reservoir just outside of Belo Horizonte, Brazil

13 Schistosoma haematobium
Eggs are eliminated with feces or urine .  Under optimal conditions the eggs hatch and release miracidia , which swim and penetrate specific snail intermediate hosts .  The stages in the snail include 2 generations of sporocysts and the production of cercariae .  Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host , and shed their forked tail, becoming schistosomulae .  The schistosomulae migrate through several tissues and stages to their residence in the veins ( , ).  Adult worms in humans reside in the mesenteric venules in various locations, which at times seem to be specific for each species .  For instance, S. japonicum is more frequently found in the superior mesenteric veins draining the small intestine , and S. mansoni occurs more often in the superior mesenteric veins draining the large intestine .  However, both species can occupy either location, and they are capable of moving between sites, so it is not possible to state unequivocally that one species only occurs in one location.  S. haematobium most often occurs in the venous plexus of bladder , but it can also be found in the rectal venules.  The females (size 7 to 20 mm; males slightly smaller) deposit eggs in the small venules of the  portal and perivesical systems.  The eggs are moved progressively toward the lumen of the intestine (S. mansoni and S. japonicum) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively .  Pathology of S. mansoni and S. japonicum schistosomiasis includes: Katayama fever, hepatic perisinusoidal egg granulomas, Symmers’ pipe stem periportal fibrosis, portal hypertension, and occasional embolic egg granulomas in brain or spinal cord.  Pathology of S. haematobium schistosomiasis includes: hematuria, scarring, calcification, squamous cell carcinoma, and occasional embolic egg granulomas in brain or spinal cord. Human contact with water is thus necessary for infection by schistosomes.  Various animals, such as dogs, cats, rodents, pigs, hourse and goats, serve as reservoirs for S. japonicum, and dogs for S. mekongi. Geographic Distribution: Schistosoma mansoni is found in parts of South America and the Caribbean, Africa, and the Middle East; S. haematobium in Africa and the Middle East; and S. japonicum in the Far East.  Schistosoma mekongi and S. intercalatum are found focally in Southeast Asia and central West Africa, respectively.

14 In endemic areas, most at risk are school-age children, women, and those involved in occupations such as irrigation, farming and fishing.

15 Then there is the North American schistosome-induced pathology ---
Duck schistosomes Raccoon schisto;… etc. Sign on the door leading out of a resort to Lake Bemidji, in Minnesota (the advice can’t hurt, but may not help either Cercarial Dermatitis

16 The 2 faces of schistosomiasis
‘Intestinal’ asymptomatic schistosomiasis at the Egyptian village level Egyptian boy with hepatosplenomegaly, ascites fluid build-up and superficial collateral circulation (NAMRU-3 clinical ward in Cairo)

17 BLOOD FLUKES Clinical manifestations of Hepatosplenic Shistosomiasis: eosinophilia, polyps in colon, fever, anorexia, weight loss, anemia, portal hypertension; cirrhosis of liver; pruritic skin rash. Eggs go back through portal circulation to liver, causing hepatomegaly, liver tenderness. Clinical manifestations of Urinary Schistosomiasis: eosinophilia, hematuria, terminal dysuria (pain, difficulty at the end of urination); obstructed urine flow.

18 The abdomen of an 11-year-old boy with intestinal schistosomiasis with the size and extent of the liver and spleen marked, indicating the severity of infection. The disease has caused a stunting of the boy's growth, he is only 120cms tall and weighs 22 kg.

19 BLOOD FLUKES Laboratory diagnostics of Hepatosplenic Schistosomiasis: eggs with lateral spine in feces Laboratory diagnostics of Urinary Schistosomiasis: eggs with terminal spine in urine Prevention: involves proper disposal of human waste and eradication of the snail host when possible. Swimming in endemic areas should be avoided.

20 S. manosni egg: prominent lateral spine
Ovoid (140X61µ) S. haematobium egg: prominent terminal spine, ovoid (150X62µ) S. japonicum egg: lateral spine obscured, round (100X60µ) Morphology of the Eggs of the 3 Key Schistosomes That Infect Humans

21 Control programs Large scale population based chemotherapy
Environmental modification Controlling snail habitat Use of molluscicides Behavioral modification Difficult and costly to sustain

22 How can I prevent schistosomiasis?
Avoid swimming or wading in fresh water when you are in countries in which schistosomiasis occurs. Swimming in the ocean and in chlorinated swimming pools is generally thought to be safe.

23 LUNG FLUKE: PARAGONIMUS WESTERMANI - an agent of paragonimiasis
Distribution: Far East, Central America, Africa, and India. Morphology: an egg-like form of the body, from 7,5 to 16 mm.

24 LUNG FLUKE Mode of transmission: ingestion of metacercaria in crabs or crayfish. Final hosts: carnivoirous mammals, pigs, humans. Intermediate hosts: 1) snail (sporocyst, redia, cercaria); 2) crabs or crayfish (metacercaria). Infective stage: metacercariae

25 LUNG FLUKE Clinical disease: a chronic cough with bloody sputum, dyspnoa, pleuritic chest pain, and pneumonia. Laboratory diagnosis: eggs in sputum or feces. Prevention: cooking crabs and crayfish properly.

CLONORCHIS SINENSIS – oriental small biliary (liver) fluke, causes Clonorchiasis. Distribution: endemic in Far East, China, Japan, and Vietnam. Localization: bile ducts, gallbladder, and pancreas.

27 CLONORCHIS SINENSIS Morphology: the adult worms are 1 to 2 cm; the eggs are small, brownish.

28 CLONORCHIS SINENSIS Transmission: fecal-oral (ingestion of contaminated raw, frozen, dried, pickled, and salted fish). Infective stage: metacercariae. Final hosts: carnivorous mammals and humans. Intermediate hosts: 1- snail (miracidium, sporocyst, rediae, cercariae), 2 - fish Cyprinidae genus- the family that includes carp and goldfish (metacercariae).

29 CLONORCHIS SINENSIS Clinical disease: cholecystitis and cholelithiasis, hepatic colic, associated with profound weight loss and diarrhea. An individual fluke may live for years in the liver. In humans a heavy infestation of liver flukes may cause cirrhosis of the liver and death. Laboratory diagnosis: immature eggs in feces Prevention: adequate cooking of fish and proper disposal of human waste

30 FASCIOLA HEPATICA an agent of fascioliasis. Distribution: endemic in Far East. Localization: bile ducts, gallbladder, and pancreas. Morphology: large size (3-5 cm) and conical form of the body; possess sucking disks (oral and abdominal) that provide them motion. Multibranched uterus is situated under the abdominal sucking disk. Testis are branched too and situated in the middle part of the body.

Final host - herbivorous mammals (horses) and humans. Intermediate host — the snail Limnea truncatula. Transmission: fecal-oral (ingestion of water , some non-water plants and vegetables, which contain adolescariae). Invasive stage: adolescariae.

32 FASCIOLA HEPATICA Clinical disease: Parasites obstruct bile ducts and lay eggs within them, leading to cholelithiasis (gallstones). Biliary obstruction can occur, sometimes causing biliary cirrhosis. Diagnosis: immature eggs in feces. An egg has large sizes, thin membrane, yellow color and small cover in one pole. Prevention: involves not eating wild aquatic vegetables.

small biliary fluke, causing Opisthorchiasis. Distribution: Siberia. Morphology: flat, the length of the body 4-13 mm. In the middle part of the body there is a branched uterus. Behind it there is a round ovary. There is a roseolla-like testis in the back of the uterus - a diagnostic sign of this worm.

Life-cycle: Final host - carnivorous mammals and humans. Intermediate hosts: 1) snail Bithynia leachi genus; 2) fish. Transmission: ingestion of contaminated raw, frozen, dried, pickled, and salted fish, which contains metacercariae. Invasive stage: metacercariae in fish muscles. Localization: bile ducts, gallbladder, liver.

35 Clinical disease: cholecystitis and cholelithiasis, hepatic colic, cirhosis. Clinical picture is very similar to Clonorhis infection. Infection can lay dormant for several years before presenting clinically. Diagnosis: immature eggs in feces, in fluid from biliary drainage, or duodenal aspirate. Eggs are mcm in sizes, have oval form and yellow color. The outer membrane is thick, and there is a cover in the front of the egg. The internal structure of the egg is microgranular. Prevention involves not eating undercooked or contaminated raw, frozen, dried, pickled, and salted fish; eradication of snail hosts when possible.

36 DICROCOELIUM LANCEATUM – causes Dicrocoeliasis
Distribution: worldwide. Localization: bile ducts, gallbladder and liver of mammals (cattle, horses). Very rare in humans. Morphology: the worms are 1 cm long with lanceolate form of the body; the intestine (gut) has two nonbranched channels which are situated in the lateral sides of the body. Two round testis are situated in the front of the body - the diagnostic sign of this worm.

Life-cycle: Final host - herbivorous mammals (cattle, horses). Intermediate hosts: 1) the snail of Zebrina and Helicela genus, 2) ants Fornica genus. Transmission: ingestion of plants with the ants, which contain metacercariae. Diagnosis: immature eggs in feces. An egg have oval form, smooth membrane, brown color, a cover is present in the front end. Prophylactics: eradication of the snails, ants when possible; dehelmithization of cattle.

38 Tapeworms (Cestoda) consist of a rounded head, called a scolex, and long strobila or chain of proglottids (multiple segments) of varying stages of maturity. They have no digestive tract of its own at any point in its life cycle. The scolex has specialized means of attaching to the intestinal wall, namely suckers, hooks, or sucking grooves. All cestodes have stage of larva and stage of oncosphere in the life cycle.

39 General Body Shape of a Tapeworm
Scolex Neck Strobila made up of proglottids

40 Scolices Suckers and hooks

41 Scolex (pl: Scolices) Bothria – with slit-like groove with weak suction powers and usually two in number

42 Neck Undifferentiated stem cells that give rise to proglottids in strobila.

43 Proglottids Unique structure of Cestodes
Contains both male and female organs Essentially a whole reproductive package in one segment of the strobila.

44 Integument Microtriches (like Microvilli of vertebrate small intestine), on surface of proglottid. Absorb nutrients

45 Proglottid RED = Male BLUE = Female

46 Systematics Order Pseudophyllidea Order Cyclophyllidea
Family Diphyllobothriidae Diphyllobothrium latum Order Cyclophyllidea Family Taeniidae Taenia saginata, T. solium, T. multiceps, T. hydatigena, T. pisiformis, T. taeniaeformis, T. ovis Echinococcus granulosus Family Dilepididae Dipylidium caninum Moniezia benedeni, M. expansa Anoplocephala spp.

47 } Life Cycles Adult Egg Coracidium Intermediate Host Oncosphere
Definitive Host Life Cycles Adult Egg } Coracidium Intermediate Host Oncosphere Cysticercus Hydatid Cysts

48 Taenia solium The adult form of T. solium causes taeniasis solium. T. solium larvae cause cysticercosis. Distribution Teniasis and cysticercosis occur worldwide but is endemic in areas of Asia, South America, and eastern Europe Morphology T. solium can be indentified by its scolex with 4 suckers and circle of hooks and by its gravid proglottids, which have 7-12 primary uterine branches. Larva of T.solium called cysticercus. A cysticercus consist of a pea-sized fluid-filled bladder with an invaginated scolex.

49 Taenia solium

50 Taenia solium Life cycle Transmittion: fecal-oral
Definitive hosts – humans Intermediate hosts - pigs Humans can be infected by eating raw or undercooked pork containing the larvae cysticercus. In the small intestine, the larvae attach to the gut wall and take about 3 months to grow into adult worm. The gravid terminal proglottids detach daily, are passed in the feces.


52 Taenia solium Distinct difference with T. saginata is that humans can be infected with egg stage and onocosphere migrates to some site in body and develops into cycticercus This can be serious, called Cysticercosis

53 Taenia solium Most common tissues in order: Connective tissues Eye
Brain Muscles Heart Liver Lungs

54 Taenia solium When in brain, may cause severe central nervous system dysfunction. Most common and distinct symptom is sudden onset epilepsy. Brain imaging can now spot cysticercus in brain.

55 Taenia saginata Beef tapeworm
Most common tapeworm in humans. Large species reaching up to 20 m. No hooks on scolex.

56 Taenia saginata causes taeniasis saginata. Distribution: occur worldwide but is endemic in areas of Asia, South America, and eastern Europe. Morphology. T. saginata can be indentified by its scolex with 4 suckers without hooklets. Its gravid proglottids have primary uterine branches. Larva of T.saginata called cysticercus. Transmittion: fecal-oral Invasive stage: cysticerci


58 Life cycle Taenia saginata Definitive hosts: humans
Intermediate hosts: cattle Humans can be infected by eating raw or undercooked beef containing larvae. In the small intestine, the larvae attach to the gut wall. The gravid terminal proglottids detach, are passed in the feces, and are eaten by cattle. Laboratory diagnosis: gravid proglottids (with uterine branches) may be found in the stools. Prevention. Prevention of taeniasis saginata involves cooking beef adequately and preventing cattle from ingesting human feces by disposing of waste properly.

59 Taenia saginata - Beef tapeworm
Beef Tapeworms do not cause a serious disease. Usually asymptomatic but may cause dizziness, abdominal pain, diarrhea, headache and nausea. Proglottids obvious in feces.

60 Clinical manifestation of teniasis soleum and teniasis saginata: abdominal pain, nausea, diarrhea, weight loss, infection may by asymptomatic

61 Diphyllobothrium latum Fish tapeworm
Important parasite of man. Definitive hosts can be humans, dogs, foxes, cats, mink, bears, and seals.  Site of attachment : small intestine. In humans the tapeworm can reach a length of 10 meters (>30 feet) and produce over a million eggs a day! .

62 Diphyllobothrium latum, the fish tapeworm, causes diphyllobothriasis
Distribution: Scandinavia, northern Russia, Japan, Canada, USA. Morphology. Diphyllobothrium latum can be indentified by its scolex with 2 elongated sucking grooves by which the worm attaches to the intestinal wall. The proglottids are wider than they are long, and the gravid uterus is in the form of a rosette. Adult worm is the longest of the tapeworms, measuring up to 13 m. Larva called plerocercoid.

63 Diphyllobothrium latum
Definitive hosts: humans Intermediate hosts: 1)copepod crustacea 2) freshwater fish Humans infected by eating raw or undercooked fish containing plerocercoids In the small intestine, the larvae attach to the gut wall and develop into adult worms. Gravid proglottids release fertilized eggs. The immature eggs must be deposited in fresh water for the life cycle to continue. Transmittion: fecal-oral Invasive stage: plerocercoid


65 Clinical disease: infection by D
Clinical disease: infection by D.latum causes little damage in the small intestine. In some individuals, megaloblastic anemia occurs as a result of vitamin B12 deficiency caused by preferential uptake of the vitamin by the worm. Most patients are asymptomatic, but abdominal discomfort and diarrhea can occur. Diagnosis depends on finding the typical eggs, oval, yellow-brown eggs with an operculum (lidlike opening) at one end, in the stools. Prevention involves adequate cooking of fish and proper disposal of human feces.

66 Hymenolepis nana (dwarf tapeworm) is found worldwide, commonly in the tropics
Morphology. It is only 2-3 cm in length. Scolex has round form and contain suckers and hooks. A neck is very long and thick. Strobila has 200 proglottides. The uterus has an excretory ostium. Eggs are released from it into the feces. Transmission: fecal-oral (by the ingestion of eggs from contaminated food or water). Invasive stage:egg.

67 Hymenolepis nana Clinical disease: asymptomatic, but diarrhea and abdominal cramps may be present. Diagnosis can be proved by observing eggs in stool. Prevention consists of good personal hygiene and avoidance of fecal contamination of food and water.

68 Echinococcus granulosus
Smallest tapeworms in Family Taeniidae. Normally in small intestine of Canines, as definitive hosts. Dogs are infected when they eat infected herbivores (sheep, goats, camels, reindeer, pigs, etc.) Occasionally infect humans. The hyatid cysts grow very slowly and can overcrowd organs.

69 Echinococcus granulosus (dog tapeworm)
is found primarily in shepherds living in the Mediterranean region, the Middle East, and Australian, USA (western states). Morphology. Worm is up to 3-5 mm. Scolex has suckers and hooks. A neck is short. Strobila has 3-5 proglottides. Posterior segment (mature) is the largest and contains uterus with the haustrums, genital pore situated in the back of the proglottid.

70 Transmission: fecal-oral
Invasive stage:egg Life cycle. Definitive hosts: dogs. Intermediate hosts: sheep, humans. Worms in the dog’s intestine liberate thousands of eggs, which are ingested by sheep (or humans). The oncosphere embryos emerge in the small intestine and migrate to the liver also to the lungs, bones, and brain. The embryos develop into large fluid-filled hydatid cysts The life cycle is completed when the entails of slaughtered sheep are eaten by dogs.


72 Diagnosis: made by Clinical manifestations
Diagnosis: made by Clinical manifestations. asymptomatic, but liver cysts may cause hepatic dysfunction. Cysts in the lungs can erode into a bronchus, causing bloody sputum, end cerebral cysts can cause headache and focal neurologic sings. Diagnosis: made by routine X-ray, observation of eosinophilia, serologic tests. Prevention of human disease involves not feeding the entrails of slaughtered sheep to dogs.

73 Echinococcus multilocularis
is found in northern Europe, Siberia, Canada, the USA. Many of the features of this organism are the same as those of E. granulosus, but the definitive hosts are mainly foxes and the intermediate hosts are various rodents. Humans are infected by accidental ingestion of food contaminated with fox faeces.

74 The disease occurs primarily in hunters and trappers
The disease occurs primarily in hunters and trappers. Within the human liver, the larvae form multiloculated cysts with few protoscoleces. The cysts continue to proliferate, producing a honeycomb effect of hundreds of small vesicles (without fluid). The clinical picture usually involves jaundice and weight loss.

75 Thank you for attention !

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