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The significance of Medical Parasitology

The significance of Medical Parasitology. The significance of Medical Parasitology. Prevalent infections worldwide Significant morbidity & mortality Significant impact on economic & social development Increased mobility of individuals & populations

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The significance of Medical Parasitology

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  1. The significance of Medical Parasitology

  2. The significance of Medical Parasitology • Prevalent infections worldwide • Significant morbidity & mortality • Significant impact on economic & social development • Increased mobility of individuals & populations • Drug resistance, climate change & opportunistic infections

  3. Global estimates of parasitic diseases and disease burden (Topley & Wilson, 2005)

  4. Definitions of parasitism • Concept of metabolic dependence (Smyth) (nutrition, developmental stimuli, control of maturation) • Genetic complementation • Population dynamic approach (Crofton)- lethal level, overdispersion, reproductive rate

  5. Parasitic adaptations • Morphological adaptations • Biochemical changes • Specialized mechanisms for entry • Complex life cycles and transmission opportunities • Mechanisms for immune evasion • Impact on host versus impact of host

  6. Parasitic adaptations

  7. Important parasitic groups • Microparasites (Protozoa) • Kinetoplastida • Ciliophora • Apicomplexa • Macroparasites(Helminths, Arthropods) • Platyhelminthes • Nematoda • Arthropoda

  8. Important issues associated with parasites of human importance • Life cycle and transmission • Pathology and symptomatology • Epidemiology, human behaviour and at risk groups • Medical history • Diagnostic difficulties • Prevention and control

  9. Approach to the patient • Full history required particularly travel history • Symptoms may be subtle and may change over time (repeated history taking) • General history also important - occupation, hobby and leisure activities, diet, drugs taken. • Clinical exam

  10. Life cycle and routes of transmission • Diverse routes of transmission which relate to human behaviour and risk factors • e.g. Toxoplasma gondii • Diverse routes of transmission with implications for parasite survival and pathogenicity • e.g. Strongloides stercoralis

  11. Toxoplasma Life cycle

  12. Strongyloides life cycle

  13. Symptomatology and pathology 1 • Parasites often provoke nonspecific and diverse symptoms • e.g. Toxocariasis in children • Microparasites often provoke more acute disease compared to the chronicity of macroparasites • e.g. Plasmodium falciparum versus Strongyloides stercoralis in returned travellers

  14. Symptomatology and pathology 2 • Differential pathology • Immunocompromised versus Immunocompetent hosts • e.g. Toxoplasma gondii & Cryptosporidium parvum

  15. Epidemiology • Changes in human behaviour • Migration and International travel • Exotic foods • Pet ownership (including exotic pets) • Intensification of agricultural practices • At risk groups • Age, Occupation, Immune status, Pregnancy, Organ transplantation

  16. Diagnostic dilemmas • Different diagnostic tests for different patient groups • Toxoplasma gondii • Need for repeat diagnostic testing • Giardia intestinalis • Need for improved sensitivity of diagnostic methods • Strongyloides stercoralis & Taenia solium

  17. Prevention and control

  18. Dracunculus medinensis : guinea worm

  19. Prevalence of important Microparasites • Malaria : 500 million (annual deaths 2.2 to 2.5 million) • Giardiasis : 200 million • American Trypanosomiasis : 16-18 million (annual deaths 60,000) • Leishmaniasis : 12-13 million • Amoebiasis : 500 million

  20. Prevalence of important Macroparasites • Cestodiasis : 70 million • Schistosomiasis : 200 million (annual deaths 500,000 to 1 million) • Lymphatic filariasis : 78.6-90 million • Onchocerciasis : 17.5 million • Ascariasis : 1.3 billion • Hookworm : 1 billion • Strongyloidiasis : 80-100 million

  21. Three vector-borne protozoa: Leishmaniasis, African Trypanosomiasis & Chagas disease Three bacterial infections: trachoma, leprosy and Buruli ulcer Seven helminth infections: hookworm, ascariasis, trichuriasis, lymphatic filariasis, onchocerciasis, guinea worm & schistosomiasis Cysticercosis, food-borne trematodiasis & some other parasitic infections could be included The Big Three and Neglected tropical diseases (NTDC) From Hotez et al, 2006, PLoS Medicine

  22. Implications of co-infections

  23. Challenges • Rare diseases • Echinococcus multilocularis : alveolar echinococcosis (AE) • Emerging diseases

  24. Toxoplasmosis • Malaria • Schistosomiasis • Neurocysticercosis • Lymphatic filariasis

  25. Texts • Topley and Wilson’s Microbiology and Microbial infections Parasitology (2005). Eds Cox, F.E.G., Wakelin, D., Gillespie, S.H and D.D. Despommier. 10th Edition. Hodder Arnold. • Peters, W. and Pasvol, G. (2007). Tropical Medicine and Parasitology. Mosby 6th edition.

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