醫(yī)學(xué)寄生蟲學(xué)：Toxoplasma gondii（弓形蟲）1

1、Toxoplasma gondii（弓形蟲）2016-12-13CONCEPTION Initially found in 1908 as a tissue parasite of gondi (an African rodent) The pathogen of toxoplasmosis Toxoplasma. gondii infection is distributed worldwideBroad host: carnivores, herbivores, birds Intracellular parasite of many kinds of tissues, muscle, i

2、ntestinal epithelium all nucleated cells. “A highly successful parasite”T. gondii is an obligate intracellular parasiteAll apicomplexa T. gondii only replicates within nucleated cells, one species High/Low toxicity strain, RH/Beverley strainThree clonal genotypes, I - III strains. Animals - Type III

3、 Most humans I, II strains ( mostly AIDS patients). MORPHOLOGYTACHYZOITE （速殖子）BRADYZOITES（緩殖子 ）（Tissue） CYST Pseudocysts(假包囊)OOCYST（卵囊）SPOROCYST (孢子囊）Crescent shaped （sunflower seed) 2 by 6 m Asexual form Endodyogeny（孢內(nèi)生殖） It can infect phagocytic and non-phagocytic, nucleated cells.Organelles: pell

4、icle薄膜, apical rings, polar rings, conoid 圓錐體, rhoptries 棒狀體, micronemes微線體, dense granules, apicoplast頂質(zhì)體 , acidocalcisome, micropore, subpellicular microtubules, mitochondrion, endoplasmic reticulum, Golgi complex, ribosomes, rough and smooth endoplasmic reticulum, nucleus. THE TACHYZOITE (速殖子） M.

5、 Black and J. C. Boothroyd (2000).The lytic cycle of Toxoplasma gondii. Microbiology and Molecular Biology Reviews, 64 (3) p. 607Am, amylopectin granule(淀粉顆粒）; Co, conoid; Dg, electron-dense granule; Go, Golgi complex; Mn, microneme; No, nucleolus；Nu, nucleus; Pv, parasitophorous vacuole; Rh, rhoptr

6、y. Dubey, et al (1998). Clinical Microbiology Reviews, 11: 267-299.The tachyzoiteCarey et al, (2004) PNAS 101: 7433THE CYTOSKELETON OF TOXOPLASMAThe anterior end of the parasite is enlarged in the box to the left so as to illustrate the preconoidal rings (CR), the conoid (C), the two apical microtub

7、ules (M), and the polar ring (PR) from which 22 subpellicular microtubules (SPM) emanate. The IMC is located just beneath the plasma membrane from the anterior to the posterior poles and is interrupted only by the micropore (MP) located in the middle of the parasite body. This pore is believed to be

8、 the primary portal through which endocytosis takes place.M. Black and J. C. Boothroyd (2000). The lytic cycle of Toxoplasma gondii. Microbiology and Molecular Biology Reviews, 64 (3) p. 607Micrograph by J. Boothroyd and D. Ferguson.圓椎體Hu, K. et al. J Cell Sci 2004;117:5697-5705Structure of Toxoplas

9、ma gondii類錐體 IMC inner membrane complex subpellicular microtubules The IMC extends， the nucleus (N) and mitochondrion (Mitoch.) divide into these membranous outlines. Nascent apical organelles (NO) develop within the anterior poles as the daughter cells grow. The entire cytoplasm is divided between

10、the daughters and the IMC of the mother dissociates. A cleavage furrow divides the cells from the anterior pole. This division continues down the length of the cells until it reaches the posterior end, where it can leave a residual body connecting the two daughters. Diagram of endodyogeny (孢內(nèi)生殖）M. B

11、lack and J. C. Boothroyd (2000). The lytic cycle of Toxoplasma gondii. Microbiology and Molecular Biology Reviews, 64 (3) p. 607Transendothelial migration peripheral blood monocytes infected by Toxoplasma gondii can be actively function as Trojan horses for parasite spread in the bloodstream.The inf

12、ection increases monocyte integrin Mac-1 (CD11b/CD18) expression, enhance the fluidic shear stress to push more transendothelial migration (TEM) then normal. Visualizing the trans-endothelial migration (TEM) of T. gondiiinfected primary human monocytes during the initial minutes following contact wi

13、th human endothelium. 4.5 times fasterNormal InfectedTACHYZOITE 1The acute infection is carried by tachyzoite stageTachyzoites divide rapidly and aggressively destroy tissuesAll pathology is associated with tachyzoitesTachys can cross the blood-brain barrier and the placentaTACHYZOITE 2BRADYZOITESPs

14、eudocysts（假包囊）When the IR slows down tachy replication, they differentiate in bradys and form tissue cysts Bradyzoite cysts are highly infective if ingestedCysts form in brain and skeletal muscleA highly stretched tissue cyst with more than 1,000 bradyzoites inan impression smear of brain homogenate

15、 from a rat 14 months after infection with the VEG strain of T. gondii. The cyst wall (arrow) is barely visible. TISSUE CYST Dubey, J.P., Lindsay, D.S. and Speer, C.A. (1998). Structures of Toxoplasma gondii tachyzoites, bradyzoites, and sporozoites and biology and development of Tissue Cysts. Clini

16、cal Microbiology Reviews, 11: 267-299.Latent bradyzoite cysts confer life-long infectionbeginning of the chronic phase of infection persist in the immune host for the rest of its liferesistant to low pH, digestive enzymes, all currently available drugsTissue cysts show very little evidence of inflam

17、mation or immune cell infiltrates.Protective cyst wall is finally dissolved and bradyzoites infect tissue and transform into tachys。Tachyzoites: pathogenesis, Bradyzoites: epidemiology TACHYZOITES（速殖子）: rapidly growing meront（分裂體） or zoite observed in the early stage of infection BRADYZOITES（緩殖子）: S

18、low-growing zoite or meront inside the tissue cysts TISSUE CYSTS: Found in the tissues contain bradyzoites Infective form. OOCYSTS（卵囊）: Zygote form. Highly resistant Infective formSporocyst (孢子囊） Sporozoites PARASITE FORMSa tissue cyst with its many bradyzoites within the brain of an infected mouse.

19、Photo courtesy of David Ferguson, Oxford University. /micro/boothroyd/boothroydlabdesc.htmlThe intestinal phase in the catCat ingests tissue cysts containing bradysNumber of merogonous cycles （無(wú)卵核受精周期) is variable；Gametocytes develop in the small intestine, more common in the ileum（回腸）. 2-4% of game

20、tocytes are male, each produces around 12 microgametes, each femal gamitocyte produce one macrogamete3-5 days after infection of cysts, oocysts appear in the cats feces with peak production around 5 and 8 dayOocysts require oxygen and they sporulate in 1-5 daysTHE OOCYST The oocyst is noninfectious

21、before sporulation (孢子形成）. Unsporulated oocysts are subspherical to spherical and are 10 by 12 m in diameter. Sporulated oocysts are subspherical to ellipsoidal and are 11 by 13 m in diameter. Each oocyst has two ellipsoidal sporocysts （孢子囊）. Sporocysts measure 6 by 8 m. Each sporocyst contains four

22、 sporozoites. Shedding（囊膜蛻落）occurs 3-5 days after ingestion of tissue cysts or 20-34 days after ingestion of oocysts. LIFE CYCLE OF TOXOPLASMA TOXOPLASMA TRANSMISSIONSources ofinfection:Contaminated water or foodUndercooked meatMother to fetusOrgan transplant (rare)Blood transfusion (rare)DEFINITIVE

23、 HOSTTransmissionby tissue cysts (containing bradyzoites 緩殖子) or by the oocyst (containing sporozoites 孢子體) Infection through ingestion of undercooked or raw meat or contaminated waterMother to fetus Toxoplasma is an opportunistic pathogen15-70% of the population is chronically infectedMost people s

24、how no or only benign symptoms (headache, sore throat, lymphadenitis, fever）Three situations can lead to severe disease:1) congenital toxoplasmosis 2) ocular toxoplasmosis in immunocompetent adults3)fatal disorders of the CNS such as encephalitis when loss of a functional immune systemPATHOGENESIS C

25、ongenital disease:（先天性疾病）acute infection of the expectant mother.Severity depends on the stage of pregnancy. Spontaneous abortions or neurological disorders such as blindness and mental retardation. Immunocompromised individuals: toxoplasmic encephalitis 弓形蟲腦炎R(shí)eactivation of a latent infection (95%

26、cases)Recently acquired infection Ocular toxoplasmosis (眼弓形體?。〤linical significance - Asymptomatic in healthy individuals- CNS involvement in immunocompromised patient- Congenital diseaseCongenital toxoplasmosis is a problem in 1/1000 pregnanciesFirst pregnancy， parasite transfer the placenta and ca

27、use fetal diseaseearly: low transmission, but severe disease, late: high transmission, more benign symptomsscreen all pregnant women for acute infection efficacy of in utero（宮內(nèi)）treatment？顱內(nèi)鈣化腦積水右側(cè)小眼改變（眼炎）Congenital toxoplasmosisChildren who are asymptomatic at birth often develop disease later on, l

28、ong term treatment of these kids is quite successfulThis include antiparasitic treatment as well as symptomatic treatment against e.g. hydrocephalus （腦水腫）Despite calcification throughout the brain this 10 month old child developed completely normalGirl with hydrocephalus due to congenital toxoplasmo

29、sis. Toxoplasmic encephalitis (TE， 弓形蟲腦炎) Only 25-30% of seropositive AIDS patients develop TEInvolvement of the CNS. Symptoms: lethargy （嗜睡）, loss of memory to severe dementia （失憶到癡呆）, focal to major motor seizures （抽搐）T. gondii is a major pathogen in late stages of AIDSIn the majority of cases thi

30、s is due to reactivation of the chronic infection rather than new infectionUsually a multifocal process. Multiple brain abscesses: necrotic central zone surrounded by hyperemic region containing parasites and infiltrating mononuclear cells. Sometimes disseminated TETE can be treated with pyrimethami

31、ne(乙嘧啶） and sulfa（磺胺) but not all patients tolerate side effectsAs for all other opportunistic infections the incidence is much lower in patient on HAART (highly active antiretroviral therapy)Ocular toxoplasmosisOcular toxoplasmosis can be a sequel of congenital infection (neonatal or late forms)How

32、ever recent epidemiological studies show that it also occurs after infection of seemingly fully immunocompetent adults Severe retinochorioditis 視網(wǎng)膜脈絡(luò)膜炎(cleared yellowish zone), after treatment scaring occursThe acute phase responds well to treatment, but 80% probability of relapse and relatively poo

33、r prognosis of eyesight in the long termClinic StagesAcute infection: the first extraintestinal sites mesenteric lymph nodes, liver parenchyma. Painfull, swollen lymph gands at cervial, superclavicular, inguinal regione, flu like symptom. Subacute infection: extensive lesions in the lung, liver, hea

34、rt, brain, and eyes. More CNS damages than other organes. Chronic infection: tissue cysts formed, remain for years, death of dradyzoites elicite an intense hypersensitive inflammatory reaction. The cyst replaced by glial cells（ 膠質(zhì)細(xì)胞） in brain may develop symptoms of chronic encephalitis, blindness,

35、myocarditis, pneumonia. DIAGNOSIS OF TOXOPLASMOSISObservation of parasites in patient specimens, such as bronchoalveolar lavage material （支氣管灌洗液）from immunocompromised patients, or lymph node biopsy.Isolation of parasites from blood or other body fluids, by intra-peritoneal inoculation into mice or

36、tissue culture. The presence of Toxoplasma organisms in the peritoneal fluid 6 to 10 days post inoculation; if negative, serology can be performed 4 to 6 weeks post inoculation.Detection of parasite genetic material by PCR, especially in detecting congenital infections in utero（羊水？）.Serologic testin

37、g is the routine method of diagnosis for specific IgG or/and IgM.the pseudocysts of T.gondii can be observed in tissue sections with monoclonal antibodies. Formation of trails containing surface membrane proteins. Can be visualized by staining with antibodiesSibley, D.L., Hakansson, S., Carruthers,

38、V.B. Gliding motility: an efficient mechanism for cell penetration. (1998). Current Biology 8.CHEMOTHERAPY OF TOXOPLASMOSIS Inhibitors of dihydrofolate reductasePyrimethamine in combination with sulfonamides 乙嘧啶+磺胺類 SulfonamidesSulfadiazine, sulfamethazine, sulfamerzaine. Clindamycin Macrolides and

39、azalides 螺旋霉素類 Roxithromycin, azythromycin, clarithromycin, spiramycin TetracyclinesDoxycline, minocycline HydroxynaphthoquinonesAtovaquone. OthersEimycine, aprinocid, dapsone, quinghasou, pentamidineCombination therapypyrimethamine-dapsone, clarithromycin-minocycline,azithromycin-pyrimethamine, azi

40、thromycin-sulfadiazine, etc Biological response modifiers Cytokines (IFN-, IL-2, TNF, IL-1, IFN-) in combination with chemotherapyEpidemiologyToxoplasmosis is present in every country, seropositivity rates range from 90%。 Highest burden of CT is in South America, parts of Middle East, some low-incom

41、e countries in Africa. 巴西新生兒CT 6000-9000例/年The leading cause of death attributed to foodborne illness in the United States.The global estimated incidence of CT is 190,000 annual cases, approximately 1.5 cases of CT per 1000 live births. (Bulletin of the WHO, 2013; 91: 501-508) The global burden of c

42、ongenital toxoplasmosis: a systematic reviewPaul R Torgerson & Pierpaolo MastroiacovoVolume 91, Number 7, July 2013 a Per 100 cases.95% CI: confidence interval (置信區(qū)間)EpidemiologyInfection is often highest in areas of the world that have hot, humid climates and lower altitudes.FoodborneAnimal-to-human (zoonotic)Mother-to-child (congenital)Rare instances (transplant reciptents.)Latent Toxoplasmosis: higher frequency of road traffic ac