Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings. The Helminths

Transcription

1 The Helminths

2 Helminths (parasitic worms) Eukaryotic Multicellular animals Chemoheterotrophic Kingdom: Animalia Phylum: Platyhelminthes (flatworms) Class: Trematodes (flukes) Class: Cestodes (tapeworms) Phylum: Nematodes (roundworms)

3 We will focus on parasitic helminths Characteristics of parasitic animals They may have a reduced digestive system They may have a reduced nervous system They may have a reduced nervous system The generally have very complex life cycles Parasitic helminths go through many developmental stages in (often) several hosts Each stage is referred to as a LARVAL stage Dioecious - each adult is only one sex (most NEMATODES!) Monoecious - each adult is BOTH sexes (true hermaphrodite - most PLATYHELMINTHS! ) The generally have very complex life cycles: The DEFINITIVE HOST harbors the adult INTERMEDIATE HOSTS harbor larval stages

4 Kingdom Animalia/Phylum Platyhelminthes Platyhelminthes - "the flatworms Trematodes, or "flukes", attach to host tissue and suck tissue fluids for nutrition. Cestodes, or "tapeworms", generally exist in the G-I tract and eat a lot of their host's food! Disgustingly, they can get quite large (greater than 20 ft.). Generally monoecious

5 Phylum: Platyhelminthes/Class:Trematoda Trematodes or flukes Asian liver fluke

6 Humans as Definitive Host: the lung fluke (Paragonimus westermani) Figure 12.26

7 Schistosomiasis: a dangerous disease caused by a fluke Symptoms are caused by eggs shed into the bloodstream from the adult in a human host Female lives in a groove on the male s body Spread by feces and urine that contaminate water supplies 250 million people affected! The eggs can infiltrate and lodge in tissues Inflammatory reactions cause tissue damage called granulomas

8 Schistosomiasis S. haemotobium S. japonicum S. mansoni Swimmer s itch Granulomas in urinary bladder wall Africa, Middle East Granulomas in intestinal wall East Asia Granulomas in intestinal wall African, Middle East, South American, Caribbean Cutaneous allergic reaction to cercariae U.S. parasite of wildfowl

9 Schistosomiasis Egg and granuloma Male and female schistosomes.

10 Schistosomiasis

11 Phylum: Platyhelminthes/Class:Cestoda Cestodes or tapeworms They are intestinal parasties Scolex (point of attachment) Have no digestive system Mature proglottids (segments)

12 Humans as Definitive Host (e.g., Beef tapeworm) Taenia spp. Transmitted as larvae in undercooked meat (beef) - ova do not infect humans Taenia solium Cysticerci may develop into adults in humans, living in the colon Diagnosed by observing proglottids and eggs in feces Worm may live in the human host for 25 years and grow to 18 feet Strangely, there are often few symptoms

13 Humans as Intermediate Host (Dog tapeworm) (Echinococcus granulosis) We are a dead end in the cycle

14 Hydatid Disease (when larvae migrate to liver, lungs, brain) Echinococcus granulosus Definitive host: Dogs, wolves Intermediate host: Sheep and other herbivores; Humans Transmitted by ingesting E. granulosis eggs Treatment is surgical

15 Kingdom Animalia: Phylum Nematoda Nematoda - the "roundworms - Generally not parasites, and are very ubiquitous in soil and water. "Pinworms" and "hookworms" are the exceptions. Humans can be infected by either eggs or larvae - all are dioecious! Example: Pinworm Enterobius vermicularis Spends its entire life in a human host (G-I system), we are infected by the eggs (we are definitive host) Host is infected by ingestion of eggs - often contaminated clothing or bedding

16 Nematodes: Eggs Infective for Humans Eggs are deposited on perianal skin

17 Hookworms

18 Hookworms

19 Kingdom Animalia: Phylum Nematoda Example: Hookworm Trichinella spiralis Causes trichinellosis (trichinosis), acquired by eating undercooked pork or game animals Larvae migrate to muscles and encyst Symptoms include fever, swelling, muscle pain, and gastroenteritis Can cause death if heart muscle is affected Few cases in U.S., about 100/year, few deaths The disease is self-limiting One pork chop can contain 10,000 larvae!

20 Trichinellosis Garbage, including undercooked or raw pork 5 1 Meanwhile, other animals are infected by eating infected meat that has been dumped. Adult Trichinella spiralis develop, invade intestinal wall of pig, and produce larvae that invade muscles. Undercooked pork 3 Human eats undercooked pork containing cysts. Capsule 2 Section showing T. spiralis larvae encysted in pig s muscle tissue (capsule is 0.25 to 0.5 in length). Section of T. spiralis 4 In human intestine, cyst walls are removed, and T. spiralis adults develop. Adults produce larvae that encyst in muscles. T. spiralis adult

21 A very common hookworm: Ascariasis Ascaris lumbricoides Often diagnosed when an adult worm (about a foot long) emerges from the anus, mouth, or nose (I know ) Lives in human intestines Transmitted by ingesting Ascaris eggs Not usually severe symptoms Infects over 1 billion people worldwide Proper sanitation helps elimate risk

22 Helminthic Diseases of the Digestive System

23 Summary of genera Flukes Clonorchis, Paragonimus, Schistosomia Tapeworms Taenia, Echinococcus Pinworms Enterobius Hookworms Ascaris, Trichinella