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Understanding Protozoa: One-Cell Animal's Life Cycle & Pathogenesis

Explore the world of protozoa, from classification to reproduction, pathogenesis, and amoebic infections. Learn about various species, modes of reproduction, and clinical manifestations. Dive into the epidemiology and morphology of these fascinating unicellular organisms.

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Understanding Protozoa: One-Cell Animal's Life Cycle & Pathogenesis

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  1. Protozoa(原虫)

  2. General Account • One-cell animal – monocellular or unicellular organisms with full vital functions • Species – total named species:65,000;parasitic: around 10,000

  3. Amoebae Flagellates Sporozoa Classification of protozoa Ciliates

  4. Life cycle patterns One-host form • One stage form – Trophozoite • Two stage form – Trophozoite & Cyst Two-host form • Mammals mammals • Mammals insect vectors

  5. Mode of Reproduction • Asexual Reproduction • Binary fission – result in 2 daughter cells • Schizogony –multiple fission result in multiple cells • Budding • Exogenous budding - by external budding result in multi- cells • Endodyogony - by internal budding result in 2 cells • Sexual Reproduction • Conjugation – exchange of nuclear material of 2 • Gametogony – sexually differentiated cells unite -- zygote

  6. Pathogenesis Opportunistic & Accidental (protozoa) infections • Host Resistance • Innate immunity • Acquired immunity • Parasite Invasion • Toxin • Mechanically damage • Immune impair • Immune inhibition • hypersentivity

  7. Opportunistic parasites • Opportunistic infection • An infection by a microorganism that normally does not cause disease but becomes pathogenic when the body's immune system is impaired and unable to fight off infection

  8. Amoebic Infections • Entamoeba histolytica • Acanthamoeba • Naegleria

  9. Epidemiology • 4th leading cause of death from parasitic diseases worldwide Organism# of deaths/yr# infected Entamoeba ~75,000 ~300 million Ascaris ~200,000 ~480 million Schistosoma ~750,000 ~200 million Plasmodium 2-3 million ~500 million (Malaria) • Amoebiasis is not restricted to the tropics and subtropics, it also occurs in temperate and even in arctic and antarctic zones

  10. Contaminated water is a source of infection.

  11. Infection is common in developing countries where sanitation is poor.

  12. Amoeba in alimentary tract • Entamoeba • E. histolytica (pathogenic) • E. dispar (non-pathogenic) • E. coli(big sister) • E. hartmani(little brother) • E. gingivalis(oral) • Endolimax nana (occasionally pathogenic) • Iodamoeba butschlii

  13. Morphology

  14. Morphology Ingested RBC Endoplasma Ectoplasma Nucleus with central karyosome and finely divided chromatin granules Pseudopod E. histolyticatrophozoite

  15. Trophozoites Morphology Single nucleus with a central, dot-like karyosome

  16. Micrograph of a trophozoite ingesting a red blood cell deprived from its host.

  17. Morphology 1-4 ring-like nucleiwith finely divided peripheral chromatin Cyst wall and round shape Mature E. histolyticaCyst

  18. Morphology

  19. E. Colitrophozoites Morphology

  20. E. Colicysts Morphology

  21. E. histolytica Stages - CYSTS • Infective Stage for humans • Resistant walls maintain viability • If moist can last several weeks • Killed by desiccation orboiling • Diagnostic Stage in formed stools • Can be concentrated and stained easily • Not seen in liquid (diarrheic) stools or tissues

  22. E. histolytica Stages - TROPHOZOITES • Cause amoebiasis (damage tissue) • Spread throughout the body, but ... • Rarely transmit the infection to others • Labile in liquid stools or tissue, and • must be rapidly found or preserved (quick fixation & cold storage) for Diagnosis

  23. Life cycle

  24. Life cycle • Humans acquire E. histolytica by: • Ingestingcysts (4 nuclei mature) in fecally contaminated food or water • Rarely by directly inoculatingtrophozoites into colon or other sites • (anal sex?) • Fecal-Oral transmission (hand to mouth)

  25. Life cycle • The basic generation-cycle: cyst – lumen trophozoites – cyst • Trophozoites may invade intestine and spread • Cyst formation – essential factors: enviroment + time • Infective cysts and trophozoites pass in feces

  26. Pathogenesis General Types of Virulence Factors: • Adherence factors • 260kDa Gal/GalNAc lectin • Invasion factors • Amoeba pores • Cysteine proteinases • Endotoxins

  27. Pathogenesis Trophozoites ... • Attachto mucosal epithelial cells (MEC) • LyseMEC • Ulcerate and invade mucosa • Cause dysentery(diarrhea + blood) • Metastasize via blood &/or lymph to • Form abscesses in extraintestinal sites ...

  28. Clinical Classification of Amoebiasis(World Health Organization) • Asymptomatic Infection:"Cyst Passers/carrier” • Symptomatic Infection: • Intestinal Amoebiasis: (colon and rectum盲肠、升结肠、直肠、乙状结肠和阑尾) • Acute Dysenteric (dysentery) • Chronic Non-Dysenteric (“self-cured”) • Extra-Intestinal Amoebiasis: • Amoebic Liver Abscess (ALA) • Amoebic Pulmonary Abscess • Other sites (brain, skin, GU, ?)

  29. Clinical classification • Asymptomatic infection (carrier) >90% (E. dispar?) • Symptomatic cases <10% • 8% -10% dysentery, colitis, etc • 2% invasive amoebiasis • 0.1% deaths

  30. Acute Dysenteric Amoebiasis Clinical manifestation Symptoms: • Bloody mucoid diarrhea • RBCs and few WBCs in stools • Abdominal pain • weight loss • bloating, tenesmus(里急后重) and cramps

  31. Acute Dysenteric Amoebiasis Clinical manifestation Signs: • Fever (33%) • Tender (enlarged) liver • Stools positive for trophozoites +/- WBC • NO cyst in loose stools

  32. Clinical manifestation • Pinpoint lesion on mucous membrane • Flask-shaped crateriform ulcers Pathological changes in large intestine

  33. Chronic Non-Dysenteric Amoebiasis Clinical manifestation “self-cured” carrier state • Usually for 1 year, 37% symptomatic >5 years • Intermittent diarrhea, mucus, abdominal pain, flatulence and/or weight loss • E. histolyticatrophs in loose stools • Cysts in solid stools • Positive serology and ulcerations on sigmoidoscopy or pathologic test

  34. Amoebic Liver Abscess (ALA) Clinical manifestation Extra-Intestinal Amoebiasis • Symptoms • History of dysentery (1 yr), weight loss, abdominal pain, chest or shoulder pain • Signs • fever, hepatomegaly • Diagnostic aspiration:non-odorous, reddish-brown in color aspirate (chocolate jam) "anchovy paste" • Might find trophozoites in the aspirate • Skin inflammation

  35. Clinical manifestation Ulcers caused by invasion of E. histolytica into the liver.

  36. Clinical manifestation

  37. Clinical manifestation

  38. An Amoebic Liver Abscess Being Aspirated. • Note the reddish brown color of the pus (‘anchovy-sauce’). This color is due to the breakdown of liver cells. Gross pathology of amoebic abscess of liver. Tube of "chocolate" pus from abscess.

  39. X-ray of Amoebic Liver Abscess Clinical manifestation

  40. Diagnosis • Pathogenic diagnosis • Stool examination: • Direct Fecal Smear (trophs and cysts) • Fecal concentration and iodine dye techniques - (cysts) ZnSO4 or formalin-ether • Cultivation • DNA detection • Sigmoidoscopy • Serologic Tests (for chronic disease): ELISA, IHA (indirect hemagglutination) • Imaging: X-ray; CT

  41. trophozoite cyst specimen loose feces solid feces method direct smear with normal saline direct smear with iodine stain diseases amoebic dysentery chronic intestinal amoebiasis or carriers remarks 1.container must clean2.examined soon after they have been passed.3.select bloody and mucous portion. Stool examination

  42. Two microscopically indistinguishable Entamoeba sp. • E. histolytica • invades tissues • should always be treated • E. dispar • is non-pathogenic, even in AIDS • should not be treated

  43. Treatment of Amoebiasis • For invasive forms: metronidazole • For luminal forms: Iodoquinofonum, paromomycin, diloxanide • Do not treat asymptomatic intestinal E. dispar infection

  44. Treatment of Amoebiasis

  45. Prevention & Control • Individual measures • Diagnosis and treatment of E. histolytica patients • Safe drinking water (boiling or 0.22 µm filtration) • Cleaning of uncooked fruits and vegetables • Prevention of contamination of foods • Chemotherapeutic Trial

  46. Prevention & Control Community measures • Public services and utilities • Adequate disposal of human stools • Safe and adequate water supply • Primary health care systems • Health education (washing hands, cleaning and protecting food, controlling insects) • Specific surveillance programs and Control programs integrated into ongoing sanitation & diarrhea control • Health Regulations • Control of food vendors and food handlers • Control of flies and cockroaches

  47. Infections with Free Living Amoebae • Naegleria 耐格里属 • Acanthamoeba 棘阿米巴属

  48. Free Living Amoebae Not seenin humans Naegleria i i 10-35 µm (smaller than A. spp.) with lobate pseudopodia Acanthamoebacysts & trophs are seen in humans i 15-45 µm with filiform pseudopodia

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