Introduction to Helminthology PDF

INTRODUCTION TO HELMINTHOLOGY  Helminthology The study of free-living worms or as parasite for other organism. Helminths are multicellular organisms (metazoan), eukariot, bilaterally symmetry Can be classified according to zoological system, habitat, mode of infecti...

INTRODUCTION TO HELMINTHOLOGY  Helminthology The study of free-living worms or as parasite for other organism. Helminths are multicellular organisms (metazoan), eukariot, bilaterally symmetry Can be classified according to zoological system, habitat, mode of infection or morphology  Zoological Classification 1. Nemathelminthes (round worm) 2. Platyhelminthes (flat worm) 2.1 Trematode/Fluke (leaf worm) 2.2 Cestode (tape worm) 3. Acanthocephala 4. Nematomorpha 5. Annelida  Mode of Infection 1. Orally 2. Penetration of skin 3. Autoinfection/Retrofection 4. Bite of Arthropod 5. Transmammary 6. Inhalation CHARACTERS CESTODE TREMATODE NEMATODE SHAPE Segmented & Leaf like & non Long, tape like segmented cylindrical, non segmented SEX Not separated Not separated Separated (hermaphodite) except Schistosoma HEAD END Sucker with Sucker without No sucker, no hooks hooks hook ALIMENTARY No Yes but not Complete CANAL complete, no anus BODY CAVITY No No Yes  GENERAL Diagnosis of worm infection made by observation of 1. characteristic eggs (ova) 2. larvae (immature forms) 3. adults Eggs are much larger than protozoa; easier to observe Observe the size, shape, colour, thickness of eggshell, embryonated or not  INTESTINAL NEMATODES Nematodes are the commonest worms that infect human Cylindrical shape, has outer covering (cuticle), complete digestive system, separate sexes (females larger than males) Ova and larvae are commonly found in feces and rarely adult worm  Life Cycle of Intestinal Nematode Life cycle usually direct without the need for intermediate hosts Life cycle involves 4 larval stages, undergoing 3 molts, and 1 adult stage  Terminology Oviparous – egg laying Ovoviviparous – producing living young (larva) from eggs that hatch within the body Viviparous – producing living young (larva) and not eggs NEMATODE  MORPHOLOGY Cylindrical body, radial symmetry. Non-cellular outer c uticle. Usually bisexual, (sexes are separated) The alimentary canal of roundworms is complete, with both mouth and anus GENERAL STRUCTURE OF NEMATODE GENERALIZEDLIFE CYCLE OF INTESTINAL NEMATODES NEMATODE DEVELOPMENT  They are common and medically important. Nematodes which infect humans normally live in intestinal tract or in the tissue Most of the medically important intestinal nematodes are soil transmitted (spread by faecal pollution of the soil). E.g: Ascaris lumbricoides, Trichuris trichuria, Hookworm, Strongyloides stercoralis. Tissue nematodes are transmitted mainly by insect vectors. E.g.: Brugia spp., Wuchereria bancrofti, Loa loa, Onchocerca volvulus LIFE CYCLE OF ASCARIS LUMBRICOIDES TREMATODE (FLUKE)  CHARACTERISTICS Dorsoventrally flattened body. Bilateral symmetry. Complex outer tegument, lacks body cavity. Usually hermaphrodite, except Schistosoma Intermediate snail host. Great morphological diversity between developmental stages.  Flukes are leaf-shaped, ranging in length from a few millimeters to 7 to 8 cm. Flukes possess an oral sucker around the mouth and a ventral sucker or acetabulum that can be used to adhere to host tissues. A body cavity is lacking. Organs are embedded in specialized connective tissue or parenchyma. STAGES IN TREMATODES  STRUCTURE OF FLUKES (A) HERMAPHRODITIC FLUKE (B) BISEXUAL FLUKE GENERALIZED LIFE CYCLE OF FLUKES.  CHARACTERISTICS All cycles involve snails as intermediate hosts. Hermaphroditic flukes - Clonorchis sinensis, Fasiolopsis buski, Paragonimus westermani, and Heterophytes heterophyes. Metacercaria are infective for humans. Bisexual flukes: Schistosoma japonicum, S. mansoni and S. hematobium. Cercariae and metacercariae are infective to humans. CESTODE (SESTODA)  CHARACTERISTICS Segmented structure (segment = proglottid) adults of different species vary in length from 2-3 mm (3-4 proglottids) to 20-30 feet (thousands of proglottids). Therefore, tapeworms vary in length from 2 to 3 mm to 10 m, and may have three to several thousand segments.  BODY PARTS Scolex (head) with attachment organs & strobila (chain of proglottids). The strobila elongates as new proglottids are formed in the neck region. The segments nearest to the neck are immature (sex organs not fully developed) and those more posterior are mature.  The terminal segments are gravid, with the egg-filled uterus as the most prominent feature. No alimentary canal, absorbence across tegument. Hermaphrodite, each proglottid has male & female genital organs, male organs develop before female. GENERALIZEDLIFE CYCLE OF TAPEWORMS