PHYLUM PLATYHELMINTHES

1. PHYLUM PLATYHELMINTHES • Major characteristics • Dorsoventrally flattened • Acoelomates • Digestive tract greatly reduced or missing • Excretory system consists of flame cells or protonephridia

2. CLASSIFICATION • Great deal of work being done in Platyhelminthes systematics. • One of the most current classification schemes is given on page 189-190 of text. • The older, more traditional classification scheme is given on page 192. We will use the older, much simpler classification.

3. CLASSIFICATION • Class Turbellaria - mostly free-living flatworms (commensals) • Class Monogenea - parasitic on skin and gills of fish and amphibians. (ectoparasites) • Class Trematoda - all parasitic, called flukes • Class Cestoidea (formerly Cestoda) all parasitic, the tapeworms. Adult tapeworms found in intestine of definitive host.

4. Class Monogenea (chapter 19) • Most are hermaphroditic ectoparasites of fish, amphibians, turtles • Some are found in urinary bladder, lower intestine of frogs and turtles. • Have a direct life cycle • In nature they cause little economic damage but can be very destructive in fish farming.

5. Monogenea • Most distinguishing feature is the presence of a large attachment organ called an opistohaptor (see fig 19.12). • Have a single host.

6. Some Interesting Examples • Dactylogyrus sp - cause large kill-off in fish in commercial fish ponds. • Gyrodactylus sp. can cause large fish-kills in fishponds. These organisms are viviparous and 4 generations may be seen within an adult worm. (see fig. 19-12). • Diplozoon paradoxum - two larval forms fuse together (fig. 19-13)

7. Digenetic Trematodes • Require two or more hosts • Some very important parasites of man • Most are hermaphroditic, Schistosomes are exception being dioecious. • Some can reproduce parthenogenetically

8. Digenetic Trematode Structure

9. Trematode Reproduction • Male reproductive system • Usually contains two testes (number may vary) • Vas efferent leaves each testis and forms the vas deferens. • The vas deferens gives rise to a seminal vesicle which stores sperm • the muscular cirrus pouch stores the male copulatory organ called the cirrus.

10. Trematode Reproduction • Usually a single rounded ovary but in some species may be lobated or branched. • A short oviduct leads from the ovary and has a sphincter called the ovicapt which regulates the passage of ova. • Vitellaria or vitelline glands are important because they contribute yolk to the eggs. • Where the oviduct and the vitelline duct join there is a expansion which forms the ootype. • Mehlis glands surround the ootype and in combination with the ootype and vitelline glands forms the oogenotop or egg forming apparatus. • Beyond this, the duct expands to form the uterus and on to the genital pore.

11. Fasciola hepatica: Trematode Life Cycle Representative • Ova or egg • Miracidium • Sporocyst • (Daughter sporocyst, or redia) • Cercaria • Metacercaria • Adult

12. Stages of Trematode Life Cycle • Ova or egg - maybe a better term is shelled embryo. • Contains miracidium inside shell • Under appropriate conditions, the operculum (cap on shell) opens to allow miracidium to escape. • Many of flukes have very distinctive eggs.

13. Stages of Trematode Life Cycle • Miracidium • Ciliated organism that can be mistaken for a ciliated protozoan. • In species that hatch in water, it contains penetration glands that release histolytic or proteolytic enzymes to help penetrate snail • Some species do not hatch until eaten by snail host. In these the miracidium is not as prominent.

14. Stages of Trematode Life Cycle • Sporocyst • The miracidium develops into sporocyst often in the digestive gland of the snail. • The sporocyst is an embryonic bag or germinal sac that has asexual reproduction occurring. • The sporocyst will produce many daughter stages called rediae or in some cases daughter sporocysts. The term daughter has nothing to do with gender.

15. Stages of Trematode Life Cycle • Rediae or Daughter Sporocyst • In function they are very similar to sporocysts. • Contain digestive tract and are more active • Asexually reproduce to yield many cercariae. • Some species they can live for many years.

16. Stages of Trematode Life Cycle • Cercariae • Usually escape snail and often swim by some means of tail structure. (see fig 15.22) • Responsible for transmission from snail to the next host. • Differences in this mechanism will be discussed later

17. Stages of Trematode Life Cycle • Metacercaria • Resistant stage that is formed in many species • Cercaria that have this stage contain cystogenic glands that helps the organism encyst on vegetation. • Cercaria that form metacercaria in second intermediate hosts, often have penetration glands that enable them to penetrate the second intermediate host.

18. Stages of Trematode Life Cycle • Adult • Always found in the definitive host • Responsible for sexual reproduction • Often restricted to specific region of host. Often very host specific.

19. Stages of Trematode Life Cycle • .

21. Digenetic Trematodes: Order Strigeiformes • Superfamily Strigeoidea • Strange looking (see fig 16-1, page 234) Anterior end large spoon-shaped oral sucker with pseudosuckers on the sides • Alaria americana - • may require 4 hosts: snail, tadpole or frog,, water snake, and frog or snake eating vertebrate. • Man can become infected eating infected frogs

22. Digenetic Trematodes: Order Strigeiformes • Superfamily Schistosomatoidae - the blood flukes • Differ from other trematodes • Dioecious • Do not have second intermediate host. • Penetrate integument of definitive host • Not really flat but rounded.

23. Schistosoma sp. • Adult worms are found in blood vessels of digestive tract or urinary bladder thus called blood flukes • male worm has a split body called the gynecophoral canal. The female is usually found within this canal “safe in the arms of her lover.” She leaves only during the egg laying period.

27. Schistosomiasis • Migratory phase - 4-10 weeks after infection. Is characterized by fever and toxic or allergic reactions resulting from migration of immature organisms. Often results in bronchitis, hepatomegaly, splenomegaly, and diarrhea.

28. Schistosomiasis • Acute phase - 10 weeks to years. Eggs can become trapped and produce granulomas and scar tissue. • Form fibrous nodules called pseudotubules. • Eggs may lodge in gastrointestinal, renal, neural, and other systems. • A person infected with 50 mating pairs would be exposed to about 15,000 eggs per day for several years. ½ of eggs might remain trapped in tissues.

29. Schistosomiasis • Chronic phase - persons living in endemic regions are often asymptotic. May have mild, chronic bloody stools or urine. Often have formation of granulomas. Hepatomegaly, Spleenomegaly, Ascites (accumulation of fluid in abdominal cavity fig 16.17, page 245.

30. Epidemiology • Human waste into water. • Moslem religious practice of ablution • Agricultural projects • Irrigation extends snail habitats • Use of night soil (human feces) • Planting and harvesting of water crops • Dependence of people on rivers.

31. Epidemiology • Before the Aswan Dam was built, the region between Cairo and Aswan was subject to annual floods. The prevalence of Schistosomiasis was only about 5%. Four • years after completion of the dam the prevalence ranged from 19%-75% (average 35%) or a 7 fold increase.

32. Schistosoma sp. • Important parasites of man and some domesticated animals • Three species infect man • Schistosoma mansoni • Schistosoma japonicum • Schistosoma haematobium • similar see table 16.1 pg 237 for differences

33. Schistosoma japonicum. • Common in parts of Japan, China, Taiwan, Philippines, Thailand, and other parts of Southeast Asia. • Most pathogenic and most difficult to control • Located in blood vessels of small intestine. • Eggs may lodge in brain causing CNS damage, coma, and paralysis. • Low host specificity

34. Schistosoma mansoni • Common in Egypt, the Middle East, parts of Africa, and parts of South and Central America. • Found in portal veins draining large intestine • The sharp lateral spine is distinctive • Primary pathological effects come from the damage done by eggs.

35. Schistosoma mansoni • In heavy infections eggs become trapped in the mucous and submucosa of the gut and cause granuloma formation • If extensive, they can cause colon blockage and significant blood loss. • In liver can cause hepatomegaly. • Destruction of lungs and heart tissue. • Reservoir hosts are of limited or no importance.

36. Schistosoma haematobium • often referred to as Bilharzia after Theodore Bilharz who discovered it. • found in parts of Africa, and parts of the Middle East, southern Europe and some parts of Asia. • Found primarily in the veins of the urinary bladder. Eggs released in urine. • They are least pathogenic

37. Diagnosis, Treatment, and Control • Finding eggs in feces or urine • Biopsy - in chronic cases if eggs not passed • Treatment - very difficult - page 245-246. • Control is very difficult • Customs and traditions • Agricultural practices • Socioeconomics

38. Breakthroughs in Control • new molluscicides • Biological controls • Compeditory and Predatory snails in Puerto Rico compete with intermediate snail host • Crayfish from North America introduced into drainages of Kenya and have significantly reduced prevalence of snail hosts. • fresh water shrimp that eat snail hosts. Natives eat shrimp

39. Schistosome cercarial dermatitis or swimmers itch • Schistosomes of animals other than man (usually rodents and birds) try to penetrate the skin of man, they can not establish themselves in the blood vascular system of man. • Often cause a dermatitis which can be severe and in some cases life threatening. • Allergic reaction

40. Swimmer’s Itch

41. Order Echinostomata • Most parasites of wild animals, but a few cause diseases in man or domestic animals • have spines or scales near anterior end • Some common examples • Echinostoma revolutum • Fasciola hepatica • Fasciolopsis buski • Fasciola gigantica

42. Echinostoma revolutum • Cosmopolitan • Shows little host specificity and is common in any bird or mammal that eats molluscs, planaria, fish, or tadpoles found infected with the metacercarial stage. • Man usually becomes infected by ingesting metacercaria found in raw snails

43. Fasciola hepatica • Commonly known as the sheep liver fluke • Important parasite of sheep and cattle (other grazers) can be found in humans. • Morphology • Large size, frequently over 30 mm long • Characteristic cone-shaped projection at anterior end followed by wide shoulders

44. Fasciola hepatica adult

45. Fasciola hepatica • Adult in bile duct of definitive host passes eggs in feces. • If eggs land in water, they hatch into miracidium that actively swims until it finds an appropriate snail. • Penetrates snail, develops into germinal sac (sporocyst), asexual stages of rediae and cercariae formed.

46. Fasciola hepatica • Cercariae leave snail, encyst on vegetation, and form metacercaria. • Herbivore infected when it ingests vegetation with metacercaria. • Metacercaria develop into adult penetrates gut wall, moves to the liver. • Humans infected by eating watercress that has metacercaria on it.

48. Fasciola hepatica Pathology • Necrosis of the liver by wandering fluke • Anemia common, inflammation and damage of the bile ducts, abscesses formed • May damage other organs (eye, brain, lung) • halzoun - Ingestion of raw liver - adult worms migrate to the lungs and cause a respiratory blockage.

49. Fasciola hepatica Epidemiology • liver blockage and watercress consumption • Prevention - Eschewing (shunning or avoiding) watercress. • Rabbits are probably important in spreading • In some parts of southeastern United States, it is important parasite of domestic animals

50. Fasciolopsis buski - Intestinal fluke of man • large fluke infects man when he ingests metacercaria found on vegetation including water chestnuts, bamboo, and water caltrop. • eat these raw or peel or crack with teeth. • elimination of feces (human and animal) into water and use of night soil for farming