nematodes

• nematodes body plan 


  tube within a tube
• nematodes are 


  mainly freely living, some are parasites of humans, animals or plants
• biochemistry of nematodes

  • survive wide range of conditions
  • survive under aerobic and anaerobic conditions
  • utilise wide range of food sources
  • tough outer cuticle
• nematodes have 4 larval stages and 4 moults
• L3 larvae is infectious stage
• no asexual reproduction
• lots of eggs released for nematodes
• 9 cases of parasitism in nematodes
• Ascaris-> 200,000 eggs/day/female
• don't multiply in host
• number of adult worms is due to number of infection events of

  L3 larvae
• endemic populations definition 


  number of worms in individual is overdispersed
• intensity is important, not prevalence
• over dispersion definition


  more than 70% of worms found in less than 15% of hosts
• Ascaris lumbricoides has 


  direct life cycle
• Wuchereria bancrofti is 


  vector transmitted
• soil transmitted helminths (STHs)
• faecal oral route of infection for STHs
• STH infections are prevalent because

  • widespread distribution of nematodes
  • resilience of eggs to harsh environmental conditions
  • high number of eggs produced per parasite
  • poor socioeconomical conditions
  • lack of education
• Ascariasis life cycle

  • eggs ingested (L3)
  • eggs shed in un-embryonated state
  • into gut, then shed shell
  • migrate to lungs to mature
  • migrate back to stomach and become adults
• pathology

  • pneumonia
  • breathing difficulties
  • highly allergenic
  • abdominal discomfort
  • lots of worms -blockage
  • malnutrition of host
  • leave small intestines and enter other organs
  • bile duct blockage- causing jaundice
  • appendix
  • intestinal tract
  • enter trachea
• coprological 


  detection of eggs in faeces
• serological 


  detection of antibodies or antigens
• molecular 


  PCR detection of parasite DNA from eggs passed in faeces
• image based diagnostics to determine infection
• filariasis is a disease 


  caused by infection with Wuchereria bancrofti
• 8 species of filarial nematodes which infect humans
• lymphatic filariasis, subcutaneous filariasis and serous filariasis
• filarial worms are transmitted by mosquitoes and black flies
• Elephantiasis is a type of filariasis
• Wuchereria bancrofti life cycle (in mosquito):

  • mosquito takes blood meal
  • microfilariae shed sheath, penetrate mosquito midgut, migrate to thoracic muscles
  • L1-L3 larvae
  • migrate to head
  • mosquito takes blood meal
• Wuchereria bancrofti life cycle (in humans)

  • L3 larvae enter humans from mosquito
  • adults in the lymph
  • adults produce sheathed microfilariae and migrate into lymph and blood channels
  • mosquito takes up blood containing microfilariae
• most people are asymptomatic
• lymphoedema

  • swelling caused by fluid collection
  • make hard to fight infection
  • bacterial infections cause hardening and thickening of skin (elephantiasis)
• morbidity management

  • surgery
  • hygiene management
  • lymphoedema- continuous care
• prevention

  • no prophylactic treatment
• way to prevent LF is to avoid mosquito bites
• prevention

  • mosquito net
  • longs sleeves and trousers
  • mosquito repellent
• Ascaris treatment 


  Mebendazole- binds to beta-tubulin, good for GI infection
• Ivermectin

  • hyperpolarisation of worms, causing paralysis and death
  • due to increased permeability of cell membrane to chloride ions