Nematodes

• Nematodes

  • Roundworms are unembryonated, elongated, cylindrical in shape
  • With sensory organs known as chemoreceptors
  • The sexes are separate
  • Female may be oviparous, viviparous/ovoviparous, or larviparous
  • Developmental stage: Egg-Larva-Adult
  • 3 basic morphologic forms: Eggs, Larvae, Adult
  • Female worms are usually larger than the adult males
  • Complete digestive and reproductive system
• Digestive system


  • Mouth (hooks, teeth, plates and other structures)
  • Buccal Cavity (tubular or funnel-shaped)
  • Esophagus (a muscular tube that pumps food posteriorly into the intestine)
  • Intestine (a flattened tube with a wide lumen that follows a straight course from the esophagus to the rectum)
  • Rectum (Defecation occurs when the anus is dilated and the pseudocoel pressure forces the feces out)
• Class Enoplea (Class Adenophorea; Class Aphasmidea)


  Without caudal chemoreceptor organ (phasmids)
• Class Rhabditea (Class Secernentia; Class Phasmidea)


  With caudal chemoreceptor organ (phasmids)
• Classification according to habitat

  • Intestinal nematodes
  • Extraintestinal nematodes
• Roundworms are unembryonated, elongated, cylindrical in shape.
• Enterobius vermicularis


  Pinworm, seatworm, society worm, oxyuris
• Enterobius vermicularis (Enterobiasis, pinworm infection)

  • Eggs are oval, flattened on one side, and loopsided
  • Adult females are yellowish-white and oviposit eggs at the perianal region at night
• Enterobius vermicularis is the final host, inhabits the large intestine, and the diagnostic and infective stages are ova and adult, and fully embryonated egg respectively. The mode of transmission is ingestion and inhalation.
• Trichuriasis, whipworm infection


  • Eggs are barrel-shaped, foot-ball shaped, japanese lantern & lemon shaped, with a prominent hyaline polar plug visible at each end
  • Adult anterior end is colorless and contains a slender esophagus, while the posterior end is pinkish-gray and resembles a whip handle. Adult males are usually smaller than females and have a curled tail.
• Trichuris trichiura is the final host, inhabits the large intestine, and the diagnostic and infective stages are ova and fully embryonated eggs respectively. The mode of transmission is ingestion.
• Ascaris lumbricoides

  Large intestinal roundworm, roundworm of man
• Ascariasis, roundworm infection

  • Egg shell consists of 3 layers: inner: vitelline membrane, middle: glycogen layer, and outermost: albuminous/mammilary coat
  • Adult has a terminal mouth with trilobate lips and a small triangular buccal cavity, and a cuticle with faint longitudinal white lateral lines
• Ascaris lumbricoides is the final host, inhabits the small intestine, and the diagnostic and infective stages are ova and adult, and fully embryonated egg respectively. The mode of transmission is ingestion.
• Necator americanus

  • New world hookworm, characteristic S-shaped adult, buccal capsule with semilunar cutting plates, equipped with an amphidial gland, tail contains a copulatory bursa and copulatory spicule
• Ancylostoma duodenale

  • Old world hookworm, characteristic C-shaped adult, adult worm has 2 pairs of ventral teeth, has a pair of copulatory spicule which is bristle like
• Ancylostoma braziliense

  • Cat hookworm, adults have a pair of teeth and a pair of inconspicuous median teeth, copulatory bursa is broad and long with short lateral rays
• Ancylostoma caninum

  • Dog hookworm, adult worm has 3 pairs of ventral teeth, has a cephalic amphidial gland
• Laboratory diagnosis of hookworms is done using DFS and Harada-Mori technique.
• Strongyloidiasis and Cochin china diarrhea

  Adult contains short buccal cavity and a long esophagus, body of the worm is transparent with fine striated cuticle, ova has a characteristic Chinese lantern shape
• Laboratory diagnosis of Strongyloides stercoralis is done using zinc sulfate concentration technique, duodenal aspirates, and Harada Mori stool culture.
• Dracunculus medinensis


  Guinea worm, Fiery serpent worm
• Dracunculosis, Dracunculiasis, Guinea worm infection

  • Larval stages include rhabditiform or first stage larvae (diagnostic stage) and third stage larvae (infective stage)
  • Adult female has a prominent rounded anterior end, while the adult male anterior end coils itself at least once
• Dracunculus medinensis has humans, dogs, cows, horses, apes, and leopards as final hosts, the adult inhabits the subcutaneous tissue while the larvae inhabit the stomach and intestinal wall, the diagnostic stage is the rhabditiform larvae and the infective stage is the third stage larvae, the intermediate host is copepods (freshwater fleas), and the mode of transmission is ingestion.
• Laboratory diagnosis of Dracunculus medinensis involves recovery of adult worms from infective ulcers and induced rupture of ulcers via immersion in cool water to reveal first stage larvae.
• Larvae


  • Hookworm: Average juvenile larvae 75-120 μm long and 4-7 μm wide, average mature larvae up to 1 mm in length
  • Threadworm: Rhabditiform larvae with a long buccal cavity and prominent genital primordium, filariform larvae lack a sheath and have a notched tail
• Trichinella spiralis


  Trichina worm
• Trichinosis, trichinellosis


  Final host is animals (zoonosis), adult inhabits the intestines and larvae inhabit the striated muscles, the diagnostic and infective stage is the encysted larvae, and the mode of transmission is ingestion
• Laboratory diagnosis of Trichinella spiralis involves muscle biopsy, blood examination showing leukocytosis and eosinophilia, elevated serum muscle enzymes, bentonite flocculation test, intradermal Bachmann, and xenodiagnosis.
• Capillaria philippinensis


  Pudoc Worm
• Capillariasis, Mystery disease


  Ova are peanut shaped with striated shells and flattened bipolar plugs, adult has a thin filamentous anterior and thicker shorter posterior, with rows of secretory cells in the esophagus termed stichocytes, female has the vulva located at the junction of the anterior and middle thirds, male has an unsheathed spicule at the posterior part
• Capillaria philippinensis has migratory birds/fish eating birds and humans as final hosts, inhabits the small intestine, the diagnostic stage is the ova and the infective stage is the larvae, the intermediate host is freshwater or brackish water fish, and the mode of transmission is ingestion.
• Laboratory diagnosis of Capillaria philippinensis involves direct fecal smear, stool concentration methods, and duodenal aspiration, with findings of low electrolyte levels and malabsorption of fats and sugars.
• Oviparous: Lays unembryonated/unsegmented eggs
• viviparous/ovoviviparous: Lays embryonated/segmented eggs
• Large adult worm


  Refers to the size of the adult Trichuris trichiura worm that inhabits the large intestine of the human host. The worm can reach lengths of up to 4 cm (1.6 inches).
• Small infective egg


  Refers to the size of the infective stage of Trichuris trichiura, which is the fully embryonated egg. These eggs are relatively small, typically measuring around 50-60 micrometers in length and 20-30 micrometers in width.