Protozoa (原虫)

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

Classification of protozoa Amoebae Flagellates Sporozoa Ciliates

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

Mode of Reproduction Asexual Reproduction Sexual 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

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

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

Amoebic Infections Entamoeba histolytica Acanthamoeba Naegleria

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

Contaminated water is a source of infection.

Infection is common in developing countries where sanitation is poor.

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

Morphology

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

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

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

Morphology 1-4 ring-like nuclei with finely divided peripheral chromatin Cyst wall and round shape Mature E. histolytica Cyst

Morphology

Morphology E. Coli trophozoites

E. Coli cysts Morphology

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

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

Life cycle

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

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

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

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

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, ?)

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

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

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

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

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

Amoebic Liver Abscess (ALA) Clinical manifestation Extra-Intestinal Amoebiasis Amoebic Liver Abscess (ALA) 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

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

Clinical manifestation

Clinical manifestation

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. 

X-ray of Amoebic Liver Abscess Clinical manifestation

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

Stool examination trophozoite cyst loose feces solid feces 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 clean 2.examined soon after they have been passed. 3.select bloody and mucous portion.

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

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

Treatment of Amoebiasis

Prevention & Control Individual measures Chemotherapeutic Trial 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

Community measures Prevention & Control 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

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

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

Acanthamoeba spp. Acanthamoeba trophozoites with acanthopodia

Primary Amoebic Meningoencephalitis PAME An acute suppurative infection of the brain and meninges that is rapidly fatal and usually not diagnosed antemortem Caused by Naegleria fowleri Headache, lethargy and olfactory problems Sore throat, runny nose, severe headache, vomiting, stiff neck, confusion leading to ... Coma and death

DIAGNOSIS Patient History (child) Symptoms/Signs PAME Prior Health Excellent Recent History of Swimming (fresh water/pools) Cases peak during HOT months Symptoms/Signs Sore throat, runny nose, headache, vomiting, stiff neck, mental confusion, olfactory problems, lethargy, coma and death

Treatment PAME None effective - few patients survive Amphoteracin B +/- ?

Granulomatous Amoebic Encephalitis GAE A more slowly progressive, chronic form of the disease not associated with swimming (except in hot tubs) cause: Acanthamoeba castellanii history of subcutaneous nodules, eye or skin infection, progressive nasal congestion, headache ... CNS lesions with negative serology for toxoplasmosis in debilitated/immuno-compromised Pts with CD4+ TL <200/mm3 disseminated infection: skin, sinuses, lungs, CNS/CSF

Pathology abscesses/lesions (tissues) have amoebae rarely seen in CSF GAE Pathology abscesses/lesions (tissues) have granulomatous inflammation hemorrhagic necrosis and vasculitis trophozoites & cysts with wrinkled-walls! amoebae rarely seen in CSF

GAE Treatment No satisfactory or effective treatment ? amphotericin B

Acanthamoeba Keratitis AK Corneal infection with Acanthamoeba spp. trophozoites & cysts Ulcerations & “Ring Infiltrate” of cornea Induced by trauma to eye, exposure to contaminated H2O contact lens wear with tap water rinsing

AK Diagnosis Treatment Examine corneal scrapings or smear Histopathologic examination of cornea Treatment Triple Antiamoebic Therapy neomycin-polymyxin-gramicidin/propamidine/miconazole Penetrating keratoplasty (cadaver cornea)

Summary E. histolytica Free living amoeba Life cycle, pathogenesis, Diagnosis, treatment carrier Morphology differences with E. coli Free living amoeba prevention

QUESTIONS How to diagnose hepatic amoebiasis? What are the transmission route of E. histolytica ? Who should be treated for amoebic infection? How will one get amoebiasis? What are the consequences?