introduction to helminthology
TRANSCRIPT
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Introduction to Helminthology
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HELMINTHES (WORMS) - Characteristics
• Eukaryotic, multicellular animals that usually have digestive, circulatory, nervous, excretory, and reproductive systems.
• Worms with bilateral symmetry, head and tail, and tissue differentiation (endoderm, mesoderm, and ectoderm).
Flatworm
Roundworm
Earthworm
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Helminthes
Two main groups (phyla)
• Platyhelminths (Flatworms)
• Nematoda (Roundworms)
Life Cycle
• Extremely complex (egg → larva → adult)
• Intermediate hosts harbor larval (developmental) stage.
• Definitive host harbors adult stage.
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Sexual reproduction strategies
Male and female reproductive organs are found in separate individuals.
One animal has both male and female sex organs (most hermaphrodites
copulate with other animals, a few copulate with themselves).
Female helminths:
Oviparous – lay eggs without embryonic development.
Ovoviviparous – embryos develop inside eggs.
Viviparous – the larva develops inside the body of the mother.
Eggs: unsegmented (no larva inside the egg) & segmented (larva inside
the egg)
1
2
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Way of transmission
• Fecal-oral
• Contaminated food, water
• Ingestion of meat (larvae)
• Through skin
• Through vector
Localization
• Intestinal helminthes
• Blood and tissue helminthes
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Nematodes (Roundworms)
• Cylindrical body tapered at each end.
• Have a complete digestive system: mouth, intestine, and anus.
• Body is covered by tough cuticle that resists drying and crushing.
• Separate males and females (males are smaller than females and have one or two spicules on posterior end).
• Infections can be caused by eggs or larvae.
• Reproduction and development:
egg → egg fertilization → embryo in egg → larva 4 molts → adult
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Nematodes - classification
Intestinal nematodes - with adults in bowel
• Ascaris lumbricoides
• Trichuris trichiura
• Enterobius vermicularis
• Ancylostoma duodenale and Necator americanus
• Strongyloides stercoralis
Tissue nematodes - adults or larval stage in tissue
• Trichinella spiralis, native etc
• Toxocara canis (visceral larva migrans)
• Filaria - Wuchereria bancrofti Brugia malayi Onchocerca volvulus Loa loa, etc.
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Cestodes (Tapeworm) - structure
• Scolex - attachment organ, contains suckers and hooks used to attach to a host organism.
• Zone of proliferation - undifferentiated area behind the scolex (neck region)
• Strobilia - chain of segments (proglottids) - square body segments used for reproduction.
Immature proglottids - developing reproductive
Mature proglottids: mature reproductive organs.
Gravid proglottids: contain eggs in the uterus.
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Immature Segment
• note that the reproductive organs are just beginning to differentiate.
Developing reproductive organs (Carmine stained)
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Mature Segments (Proglottids)
• Tapeworms are Hermaphroditic
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Cestodes (Tapeworm)
Intestinal cestodes
• Taenia solium (pork tapeworm)
• Taenia saginata (beef tapeworm)
• Diphyllobothrium latum (fish tapeworm)
• Hymenolepis nana (dwarf tapeworm)
• Hymenolepis diminutia
• Dipylidium caninum
Tissue cestodes
• Taenia solium - cysticercosis
• Echinococcus granulosus (unilocular hydatid)
• Echinococcus multilocularis (alveolar hydatid)
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Principle of stool sampling collection, handling
and processing for parasites examination
Collection and handling: • Minimum 3 samples • Clean, water-tight container with a screw-cap lid • The smallest acceptable amount of stool is 2-5g • Urine should not be allowed to contaminate the specimen • The specimen container should be labeled correctly (patients’
name, date and time of sample collection, test/tests requested, suspected diagnosis, clinical findings, travel history)
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Preservation (fixation)
• The ideal specimen is a freshly collected stool sample
• 5-10% formalin
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Processing
• Macroscopic examination:
- consistency
- color
- gross abnormalities
- blood and mucus in feces
- worms in feces
• Microscopic examination: standard procedures