Nematodes

• Nematodes


  • Ubiquitous - found everywhere
  • Some are parasitic, some are free-living
  • Live in all environments
• Nematode morphology


  • Cylindrical
  • Body wall - cuticle (colourless, helps with movement)
  • Hypodermis - cuticle secreted here
  • Musculature - contract and relax for movement
• Nematode migration


  1. Gastro-intestinal parasites remain entirely within gut during development

  2. Others migrate
• Internal cavity


  Fluid filled (suspends guts and reproduction)
• Nematode digestive system


  • Mouth
  • Buccal cavity
  • Oesophagus
  • Intestines
  • Rectum
  • Anus
• Nematode nervous system


  • Simple, for muscle contraction and digestion
• Nematode reproductive system


  • Female - oviduct, ovary, uterus, vulva
  • Male - ejaculatory duct, testes, spicules (for clasping onto female)
• Nematode life cycle


  1. Adult

  2. Egg

  3. Larval stages (with cuticle moult between each)
• Parasites migrate to ease pressure on host, keep host alive longer, access different nutrients and environments
• Arrested development (hypobiosis)


  Stimuli for mounting, L3 is most infective stage if ingested
• Most common arrested development is in L4 stage, e.g. Teladorsagia in sheep
• Arrested development can lead to inhibited development with mass emergence
• Most nematodes do not pose a zoonotic risk to humans, but some can be very harmful and migrate through the body causing organ damage
• Nematodes affecting large animals

  • Trichostrongylidae - disease in sheep and cattle, some risk for horses
  • Examples - Teladorsagia (Ostertagia), Trichostrongylus, Haemonchus
• Direct life cycle


  Larval stages remain within host gut and undertake no migration
• Indirect life cycle


  Larvae develop and become adults outside the host, then infect the host
• Different nematode species have unique predilection sites for larvae within the host
• Pre-patent period (PPP)

  Time taken from ingestion of larvae to eggs being present in faeces
• Effects of nematodes in large animals

  • Abomasum - Ostertagia, Teladorsagia
  • Small intestines - Trichostrongylus, Cooperia
• Parasitic Gastro Enteritis (PGE)


  Caused by large numbers of trichostrongylidae in the GIT, usually in young stock prior to development of immunity
• Clinical signs of PGE

  • Watery diarrhoea
  • Staining of back legs/tails
  • Dehydration
  • Lethargy
  • Weight loss
• Pathogenesis of PGE


  Damage to GIT, weight loss, anaemia, lethargy
• PGE treatment and control

  • Anthelmintics
  • Reduce contamination levels on pastures
  • Awareness of peri-parturient rise and seasonal fluctuations
• Nematodirus battus


  Found in small intestine of sheep and goats, large and long eggs that can take up to 2 years to hatch, need high and low temperatures to develop
• Nematodirus battus life cycle

  1. Egg

  2. Adult migrates in egg every year to complete cycle

  3. Egg hatched once ingested
• Control of Nematodirus battus involves changing fields, anthelmintics, and monitoring
• Pathogenesis of Nematodirus battus

  Damage to mucous lining of gut
• Dictyocaulus viviparous (lungworm)


  Host response is coughing and inflamed, frothy mucous
• Clinical signs of dictyocaulosis

  • Coughing
  • High respiratory rate
  • Salivation
  • Neck and head outstretched
• Transmission of dictyocaulosis is by ingesting larvae, treatment is with anthelmintics, and prevention is by vaccination
• Toxocara canis


  Large white nematode in small intestine of dogs, complex life cycle with hepatic-tracheal migration in young pups and reactivation of dormant larvae in pregnant bitches
• Effects of Toxocara canis

  • Stunted growth
  • Distended belly
  • Vomiting
  • Diarrhoea
  • Intestinal blockage
  • Pulmonary damage
• Visceral larva migrans


  Zoonotic condition caused by Toxocara canis, where larvae can invade muscles, liver, kidney, eyes
• Symptoms of visceral larva migrans


  • Wheezing
  • Anaemia
  • Abdominal pain
  • Swollen liver
  • Blindness
• Control of Toxocara canis involves reducing environmental egg contamination, anthelmintic treatment, and good hygiene
• Toxocara cati


  Large white nematode in small intestine of cats, eggs passed in faeces and infective larvae ingested by cats
• Effects of Toxocara cati

  • Failure to thrive
  • Dull coat
  • Diarrhoea
  • Potbelly
• Control of Toxocara cati involves anthelmintic treatment of pregnant cats and kittens
• Angiostrongylus vasorum


  Nematode found in the heart and pulmonary arteries of dogs, larvae migrate out of the heart and are coughed up and swallowed
• Clinical signs of angiostrongylosis


  • Difficulty breathing
  • Coughing
  • Heart failure
  • Asymptomatic