Parasites

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Author:
Anonymous
ID:
190975
Filename:
Parasites
Updated:
2012-12-31 11:02:11
Tags:
bod pathology parasites parasite
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Description:
1st parasite lecture
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  1. 2 types of hosts with regards to life cycles
    • Definitive: in which parasite reaches sexual maturity/ sexual reproduction occurs
    • Intermediate: required for parasite development, but parasite does not reach sexual maturity
  2. 3 major endoparasitic groups
    • protozoa (reproduce in host)
    • metazoa (no direct replication in definitive host)
    • helminths
  3. 4 types of protozoa and their diseases... where does reproduction happen?
    • Leishmania: leishmaniasis
    • Plasmodium: malaria
    • Trypanosomes: sleeping sickness
    • Babesia: tick borne diseases in cattle
  4. 3 groups of helminths
    • nematodes (ascaris, hookworms, filarial worms)
    • trematodes (schistosomes)
    • cestomes (tapeworms)
  5. 3 groups of nematodes
    • Filarial nematodes: Wuncheria bancrofti, Onchocerca volvulus
    • Ascaris (lumbricoides)
    • Hookworms (Necator americanis)
  6. why is investigating life cycles so important in parasitology?
    Numerous developmental forms may have different pathologies, have different immune evasion mechanisms, be susceptible to different control measures
  7. 2 types of life cycles of parasites
    • Direct: single host species
    • Indirect: multiple host species eg malaria with mosquito vector
  8. What is Ascaris lumbricoides? Size? Life span? Egg production?
    Hookworm (nematode), 15-35cm, 1 year, ~200,000 eggs produced per day
  9. Describe life cycle of Ascaris
    • Adults in small intestine
    • Eggs laid and passed out in faeces
    • Infective larvae within eggs
    • Ingestion
    • Larvae hatch and penetrate villi of small intestine into portal circulation
    • Arrive at lungs, mature, penetrate alveoli, coughed up, swallowed
  10. What type of immune response to intestinal helminths provoke?
    • Th2
    • IL3, 4, 5: increased IgE, eosinophils, mastocytosis
    • Increased mucus and smooth muscle contraction -> expulsion of worms
  11. How does Ascaris cause damage to host? (7)
    • Intestinal blockage (fatal with several 100 worms)
    • Lung damage (Eg pneumonia due to infection of pools of blood caused by burrowing)
    • Abdominal pain, nausea, vomiting
    • Protein and fat deficiency
    • Impaired Vitamin A absorption
    • Lactose intolerance
    • Allergic reactions to worm metabolites: rashes, eye pain, asthma
  12. Describe resilience of ascaris
    • As infective larvae within eggs, can survive in soil for over 10 years
    • Sensitive to UV light (eg sunlight)
  13. Example of Hookworm, size
    Necator americanis, 1cm
  14. Hookworm life cycle
    • Adults in small intestine, eating blood
    • Eggs passed in faeces
    • Eggs HATCH to release free living larvae
    • Infective larvae enter host by skin penetration
    • Migrate to lungs, coughed up, swallowed
  15. What do hookworms feed on?
    Blood
  16. What does Ascaris feed on?
    Liquid food in small intestine
  17. How long can hookworms live? Egg production?
    • Up to 15 years
    • around 10,000 eggs produced per day
  18. How do hookworms cause damage to host?
    • Laceration of small intestine: up to 200ml blood lost per day - anaemia
    • Abdominal pain, loss of appetite
    • Protein and iron drain: can cause catastrophic malnutrition in children with stunted growth and impaired cognitive development
  19. 6 things hookworms do to enable survival in host
    • Induce apoptosis in T cells
    • Release factors inc Superoxide dismutase (prevent ROS destruction), AchE (anti-inflammatory), proteases
    • Inhibit neutrophil migration
    • Produce anti-coagulant molecules so that blood does not clot as they feed
  20. 2 types of filarial nematodes and the diseases they cause, sizes
    • Wuncheria bancrofti: elephantiasis, 4-10 cm
    • Onchocera volvulus: river blindness, 20-50 cm
  21. Life cycles of filarial nematodes. Differences between the 2 types.
    • INDIRECT (Wb = wuncheria bancrofti, Ov = onchocera volvulus)
    • Wb in lymph nodes, Ov in subcutaneous nodules
    • Microfilaria released into blood (Wb) or skin (Ov)
    • Transmission via mosquito (Wb) or blackfly (Ov)
    • Infective larvae enter wound during feeding
  22. What parasite causes elephantiasis? Describe pathology
    • Wuncheria bancrofti
    • Live in lymph nodes, cause inflammatory response
    • Lymph return is obstructed
    • Progressive infiltration of fibrous connective tissue eg in scrotum, legs, arms
  23. What parasite causes river blindness? Describe pathology
    • Onchocera volvulus
    • Microfilaria degenerate in skin: elephantiasis, dermatitis, blindness (fibrous tissue in eye causing sclerosing keratitis)
  24. Describe bacterial symbiosis with nematodes
    Wolbacteria: use antibiotics to kill bacteria, nematodes cannot reproduce and also die
  25. Describe life cycle of Toxoplasma gondii
    • T. gondii in gut epithelial cells of cat
    • Oocysts shed in faeces
    • DIRECT: ingestion by cat
    • INDIRECT: ingestion by intermediate host (human, mouse, rat, cow, sheep, pig)
    • Cysts develop due to immune response to parasites in tissues
    • Can cross placenta and damage foetus
    • Tissues eaten by cat
  26. Describe T. gondii cell invasion
    • Active process
    • T. gondii enclosed in parastophorous vacuole: host proteins excluded from membrane to prevent degradation
  27. 2 ways in which T. gondii avoids immune system
    • Parasitous vacuole with host proteins excluded
    • Interference with NF-kB translocation to nucleus
  28. Pathogenesis in T. gondii
    • Cysts in heart, brain, CNS, skeletal muscle - can be asymptomatic for years
    • Immunosuppression: dissemination: ocular toxoplasmosis and fatal CNS disorders
  29. 4 public health measures to control parasitic diseases
    • proper sewage disposal
    • food
    • water
    • education
  30. 3 methods of vector control
    • drainage schemes
    • spraying
    • bite avoidance

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