Intro

• Helminths


  • Nemathelminths (Roundworms)
  • Platyhelminths (Trematodes - Flukes, Cestodes - Tapeworms)
• Nematode


  • Elongated and cylindrical in shape, with bilateral symmetry
  • Non-segmented
  • Rounded anterior end; tapered posterior end
  • Light cream - white in color, pinkish if well-nourished
• Body wall components


  • Cuticle
  • Hypodermis
  • Somatic musculature
• Cuticle


  Tough, elastic protective covering that is metabolically active and periodically undergoes molting (shedding of the outermost covering)
• Layers of the cuticle


  • Epicuticle (thin outermost barrier with glycocalyx)
  • Exocuticle
  • Mesocuticle (with obliquely oriented, collagenous, fibrous sublayers)
  • Endocuticle (fibrous layer with indistinct fiber orientation)

  
• Basal Lamina


  Structure that separates the cuticle from the underlying hypodermis
• Hypodermis


  Thin cellular structure that secretes the cuticle and protrudes into the pseudocoelom along the mid dorsal, mid ventral, and lateral lines to form the longitudinal hypodermal cords

  
• Somatic Musculature


  • One or more layers of longitudinally arranged muscle cells for probing and penetrating motion
  • Polymyarian (more than five per quadrant)
  • Holomyarian (one to two per quadrant)
  • Meromyarian (two to five per quadrant)

  
• Pseudocoelom


  Cavity that contains fluid called hemolymph which bathes the internal organs, offers protection by acting as a cushion, and acts as a hydrostatic skeleton
• Digestive Tract


  • Foregut (proximal)
  • Midgut (medial)
  • Hindgut (distal)
• Foregut


  • Mouth (generally has three lips)
  • Pharynx (triradiate)
  • Esophagus (may be equipped with muscular enlargement called bulbs)
• Midgut


  Contains the intestines where digestion occurs
• Hindgut


  • Male: Cloaca (contains both fecal material and ejaculatory duct)
  • Female: Rectum and anus (separate reproductive and metabolic)

  
• Nervous System


  • Circumesophageal commissure or nerve ring (ganglia from longitudinal nerves, equivalent to the brain)
  • Rectal commissure (ganglia from ventral longitudinal nerve)
• Sensory Organs


  • Mechanoreceptors (Labial papilla, Cephalic papilla)
  • Chemoreceptors (Amphids, Phasmids)
• Nematode Classes


  • Aphasmidea (Trichinella spiralis, Trichuris trichiura, Capillaria philippinensis)
  • Phasmidea (Hookworms, Ascaris lumbricoides, Strongyloides stercoralis, Enterobius vermicularis, Filarial worms)
• Reproductive Organs


  • Sexes are separate (Dioecious), some are parthenogenetic
  • Males are smaller than females, curved posteriorly
  • Females are flat posteriorly
• Male Reproductive Organ


  • Single tubule with testes, vas deferens, seminal vesicle, ejaculatory duct opening into cloaca
  • One or more chitinized copulatory spicules (equivalent to penis)
  • Sperm has no flagella or acrosomes (immotile)
• Female Reproductive Organ


  • Usually didelphic (two cylindrical ovaries expanding into uteri)
  • Symmetrical left and right uteri uniting to form a common vagina
  • Single gonophore or vulva (opening of reproductive organ to exterior, frequently near middle of body)
• Excretory System


  Renettes (large unicellular gland that empties through an excretory pore, function not conclusively known)
• Nematode Life Stages


  • Adult (diagnostic stage)
  • Ova (infective stage)
  • Larva (infective stage)
• Modes of Transmission


  • Ingestion of embryonated egg
  • Ingestion of infective larvae
  • Skin penetration
  • Mosquito-borne
  • Inhalation
  • Autoinfection
• Adult Worm Types


  • Oviparous (produces eggs, young hatches after expulsion)
  • Viviparous (brings forth live young developed inside adult female)
  • Parthenogenetic (asexual reproduction)

  
• Habitat of Adult Worms


  • Small Intestines
  • Large Intestines (Colon)
  • Tissue
  • Larva Migrans in Man

  
• Ova


  • Capillaria philippinensis
  • Enterobius vermicularis
  • Trichuris trichiura
  • Ascaris lumbricoides (corticated fertilized, corticated unfertilized)
  • Hookworm
• Larval Forms


  • L1, L2, L3, L4 (larval stages preceding each molt)
  • Rhabditiform Larvae (first stage larva of Strongyloides stercoralis and hookworms)
  • Filariform Larvae (third stage larva of Strongyloides stercoralis and hookworms, usually infective stage)
  • Microfilaria (pre-larval form of filarial worms)

  
• Molting


  • 1) Formation of new cuticle 2) Loosening of old cuticle 3) Rupturing of old cuticle 4) Escape of larva
  • Exsheathing fluid controls molting sequence
  • Supraphysiologic steroids can hasten molting in immunocompromised patients
• Hypobiosis


  Developmental arrest, lag phase at some stage of life cycle to withstand adverse environmental conditions