Introduction of helminthology

Helminthology is such an important topic not only in India but worldwide. Here is an introduction to the medically important parasites causing diseases to man.

1. Introduction to Helminthology Dr. Moumita Adhikary Assistant Professor Microbiology

2. Introduction The helminthic parasites are multicellular Kingdom : Metazoa Bilalerally symmetric animals Having 3 germ layers ( triplobastic metazoa ) head, tail and tissue differentiation (endoderm, mesoderm and ectoderm) The term 'helminth'(Greek helmins -’worm’ ) originally referred to intestinal worms, but now comprises many other worms, including tissue parasites as well as many free-living species

3. Characteristics Eukaryotic, multicellular animals that usually have digestive, circulatory, nervous, excretory and reproductive systems Parasitic helminths spend most or all of their lives in host and usually have the following specializations: May lack a digestive system . Absorb nutrients from host’s food, body fluids or tissues Have a reduced nervous system Means of locomotion is reduced or absent Complex reproductive system . Individuals produce many eggs that can infect another host

4. Classification Two main groups (phyla) 1. Platyhelminths (Flatworms )  It includes 2 classes :  Class – Cestoda (tapeworms)  Class – Trematoda (Flukes) 2. Nemathelminths : class N ematoda and 2 subclasses:  Subclass – Adenophoraea ( Aphasmidia )  Subclass – Secernentea ( Phasmidia )

5. HELMINTHOLOGY Phylum Platyhelminthes = Flat worms Class Trematoda = Flukes Class Cestoda = Tape worms Phylum Nemathelminthes = Round worms Class Nematoda Genus Ascaris Genus Trichinella Genus Necator , Ancylostoma Genus Enterobius Genus Dranunculus Genus Wucereria

6. Important Features of Helminths Adult Worms Cuticle/Integument : Outer protective covering, which may be tough and armed with spines/hooks : R esistant to intestinal digestion Mouth: Teeth/Cutting plates Suckers with/without Hooks: for attachment to host tissues Organs of locomotion: Absent, but in some species the suckers assist in movement, M ovement- by muscular contraction and relaxation Nervous system: Many helminths have a primitive one E xcretory system : is better developed

7. Reproductive system G reatest development - Monoecious (with functioning male and female sex organs in the same individual) - Diecious (the two sexes, male and female, separate ) H ermaphroditic helminths : both male and female reproductive systems are present in the same worm  self-fertilization/cross-fertilization ( e.g. Taenia solium ) In the diecious species- Male being smaller than the female (e.g. Ascaris lumbricoides ) Parthenogenic : being able to produce fertile eggs or larvae without mating with males ( e.g.Strongyloides )

8. Eggs P roduced in enormous numbers - ≥ 200,000/female/day Various helminths have distinct morphology of eggs, which can be used to differentiate the helminths Larval Forms Cestodes : C ysticercus , coenurus , coracidium , cystecercoid , procercoid , hydatid cyst, plerocercoid forms Trematodes: miracidium , cercaria , redia , metacercaria , sporocyst Nematodes : microfilaria , filalariform larva, rhabditiform larva

9. I . Platyhelminths (Flatworms ) Characters Flattened from front to back ( dorsoventrally ) , tape-like They either lack alimentary canal (as in cestodes ) or their alimentary canal is incomplete, lacking an anus (as in trematodes) Class Cestoda : Intestinal parasites Cestodes have tape-like, dorsoventrally flattened , segmented bodies T hey do not possess an alimentary system ( absorb food through cuticle) The head carries suckers and some also have hooks They possess scolex , neck and proglottids - segments They are monoecious and body cavity is absent Each proglottid has both male and female reproductive organs They are oviparous : Proglottids farthest from head are mature and contain many fertilized eggs

10. Cestode (Tapeworm) Body Structure: Scolex and Proglottids

11. Parasitic human tapeworms: Beef Tapeworm ( Taenia saginata ) : Human is definitive host. Can reach up to 6 meters in length, scolex is 2 mm long with hundreds of proglottids . Infection occurs by ingestion of contaminated, undercooked beef (“measly beef ”) Pork Tapeworm ( Taenia solium ) : Human is definitive host. Infection can occur from eating infected undercooked pork (rare in the U.S.) or from human to human contact Echinococcus granulosus : Dogs and coyotes are definitive hosts. Humans may become infected by contact with dog feces or saliva

12. Class Trematoda Trematodes have flat or fleshy , leaf-like unsegmented bodies The alimentary canal is present but is incomplete i.e., without an anus They possess suckers but no hooks The sexes are separate in the schistosomes , while the other flukes are hermaphroditic They are oviparous Leaf shaped bodies -Ventral and oral suckers for attachment and sucking fluids from host -Some can absorb nutrients through their cuticle

13. Named after host tissues in which adult lives Blood Fluke ( Schistosoma spp. ) : Cause schistosomiasis which affects over 400,000 immigrants in U.S. and 200 million people worldwide Cause damage to blood vessels, liver, and many other organs Live in waters contaminated with feces , burrow through skin of human and enter the circulatory system , particularly abdominal and pelvic veins Asian Liver Fluke ( Clonorchis sinensis ) : Infests gallbladder, bile ducts, pancreatic ducts, causes biliary cirrhosis and jaundice. Lung Fluke ( Paragonius westermani ): Lives in bronchioles of humans and other animals. 12 mm long. Infection from eating undercooked crayfish

14. Asian Liver Fluke ( Clonorchis sinensis )

15. Phylum Nemathelminthes ( Nematoda ) Elongated, cylindrical, unsegmented body (sometimes tapered at each end) Have a complete digestive system : mouth, intestine and anus Body is covered by tough cuticle that resists drying and crushing Most species are dioecious : separate males and females: oviparous/ larviparous Males are smaller than females and have one or two spicules on posterior end Over 90,000 known species. Most are free-living. Only about 50 are human parasites Life cycle : S impler than flatworms Infections : Eggs/Larvae relatively well-developed Body cavity is present The head does not have suckers or hooks, but may have a buccal capsule with teeth or cutting plates

16. Infectious eggs Pinworm ( Enterobius vermicularis ) : Spends entire life in human host. Adults live in large intestine . Female lays eggs in perianal region which causes itching . Up to 90% of children are infected through contaminated clothes or bedding. Infection usually disappears after a few years. Ascaris ( Ascaris lumbricoides ) : Large nematode , up to 30 cm . Dioecious with sexual dimorphism . Live in small intestines of humans, horses, and pigs. Eggs can survive in soil for long time. Infectious larvae Adult Hookworm ( Necator americanus ): Live in small intestine of humans, eggs are excreted in feces. Enter host by penetrating skin . Enters bloodstream, travels to lungs, swallowed in sputum. Avoided by wearing shoes. Trichinosis ( Trichinella spiralis ): Reproduce sexually in small intestine of humans. Obtained from eating undercooked pork . Larvae enter blood vessels and form cysts throughout body. Anisakines (Wriggly worms): Infected fish and squid . Killed by freezing and cooking.

17. Multiplication Donot multiply in the body of the host S ingle infection does not generally leads to disease Heavy worm load follows multiple infections Sometimes , multiplication occurs within larval forms in Platyhelminths

18. Life Cycle Extremely complex Intermediate hosts harbor larval (developmental) stage Definitive host harbors adult stage Sexual reproduction strategies: Dioecious : Male and female reproductive organs are found in separate individuals Monoecious (Hermaphroditic): One animal has both male and female sex organs. Most hermaphrodites copulate with other animals, a few copulate with themselves

19. Life Cycle • Cestodes : 2 different hosts , except Hymenolepis nana- single host Diphyllobothrium latum - 3 hosts • Trematodes : 1 definitive host (man) and 2 intermediate hosts Fresh water snail/mollusc: 1st intermediate host fish or crab act : 2 nd intermediate host except schistosomes which require 2 hosts – 1 definitive host ( man) and other intermediate host (snail ) • Nematodes: only 1 host except filarial nematodes & Dracunculus medinensis : 2 hosts