Nematoda

• Nematodes are the most numerous animals with over 28,000 described species
• Nematodes are the second most numerous species
• Nematode species are very difficult to distinguish
• Free-living nematodes


  • Abundant as decomposers in soil, aid in recycling of nutrients
• Over 16,000 nematodes are parasitic
• Nematodes are among the most successful parasites of plants and animals
• Nematodes occupy a wide range of habitats including freshwater, sea, and soil
• Nematode body


  • Thin, elongated, cylindrical and non-segmented with both ends tapered
  • Pseudocoelomates unlike flatworms

  
• Buccal cavity


  May have styles or teeth
• Nematode digestive system


  • Oral cavity opens into a muscular-sucking pharynx which connects directly to intestine (produces additional enzymes)
  • No stomach
• Nematode head


  • Radially symmetrical, rest of body is bilaterally symmetrical
  • Mouth has either three or six lips, often bear a series of teeth on their inner edge
• Nematode epidermis and body wall

  • Epidermis (single layer of cells) is covered by a thick cuticle
  • Underneath epidermis lies a layer of muscle cells, which surrounds body cavity

  
• Excretion in nematodes


  • Nitrogenous waste (ammonia form) through body wall
  • Excretory pore also present
• Ascaris lumbricoides


  Causes Ascariasis, one of the most common intestinal worm infections

  
• Ascaris lumbricoides


  • Largest nematode parasitizing human intestine
  • Adult females (20-35 cm) much larger than males (15-30 cm)
  • Male has curved posterior end, bears anal opening with pair of copulatory spicules
  • Females may produce about 200,000 eggs per day

  
• Life cycle of Ascaris lumbricoides


  1. Fertile eggs passed in faeces, embryonate & become infective after 18 days to several weeks

  2. Ingested eggs hatch in intestine, larvae burrow into intestinal wall, blood vessels & get to the liver (2nd stage larvae, 6hrs post-infection)

  3. Develop to early 3rd stage larvae in liver after few days

  4. Larvae get to heart, lungs (4 – 7 days), break out of capillaries, enter alveoli (7 or 8 days)

  5. They enter trachea, pharynx and are swallowed (8-10th day)

  6. Larvae develop into adult worms in small intestine (2-3 months post- infection, there is oviposition)

  
• Ascaris lumbricoides eggs may remain viable for up to 17 months in the environment
• Symptoms of Ascaris lumbricoides infection

  • Usually no acute symptoms
  • Infection may cause stunted growth
  • High worm burden may cause abdominal pain & intestinal obstruction
  • Pulmonary symptoms e.g. coughing
• Diagnosis of Ascaris lumbricoides

  Microscopic identification of eggs in stool

  
• Scientific classification of Ascaris lumbricoides
• Life cycle of Hookworm spp.

  1. Eggs are passed in the stool

  2. Larvae hatch in 1 to 2 days

  3. After 5 to 10 days they become filariform that are infective

  4. Filariform can survive 3 to 4 weeks (penetrate the human skin when in contact)

  5. Larvae enter blood vessels and are carried to the heart, lungs, trachea and are swallowed

  
• Hookworm


  • Adult hookworms live in small intestine of their host, attached to intestine and feed on blood and tissue
  • Female can produce up to 20,000 eggs per day after mating and passed in faeces

  
• Ancylostoma duodenale can also infect cats and dogs
• Ancylostoma duodenale can successfully enter man by oral ingestion
• Other common parasitic nematodes in humans

  • Filaria
  • Pinworms (Enterobius)
  • Whipworms (Trichuris trichiura)

  
• Life cycle of Pinworm (Enterobius vermicularis)

  1. Gravid (carrying eggs) female lays eggs on the perianal folds (around the anus)

  2. Eggs hatch in duodenum, larvae grow rapidly to 140 to 150 micrometers in size, migrate towards colon, moulting twice to become adults

  3. Females survive for 5 to 13 weeks, and males about 7 weeks

  
• Pinworm transmission


  • Through soiled night clothes, bed linens, contaminated furniture, toys and other objects
  • Handling of contaminated clothes
  • From host to host through contamination
• Pinworm symptoms


  • Most common symptom is itching in anal area, making sleeping difficult (insomnia), restlessness
  • Continuously scratching may lead to secondary infection bacterial dermatitis
  • A considerable proportion of children suffer from loss of appetite, weight loss, irritability, emotional instability
• Pinworm diagnosis


  Seen eggs under microscope, worms visible in the night

  
• Treatment and control of pinworms

  1. Albendazole and mebendazole effective for treatment

  2. Personal hygiene measures like keeping fingernails short, washing hands, changing bed covers and sleeping garments regularly, covering food, children wearing gloves while asleep, changing underwear daily

  3. Detergents have little effect on viability of eggs