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Parasitology Final Study Guide.docx

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Microbiology and Immun (Sci)
MIMM 413

Parasitology Final Study Guide Post MT Material Toxoplasmosis Dr Ndao Aside Chagas Disease can be transmitted up to 34 generations ParasitesSome of the parasites that we will discuss are bioterrorism organisms if they are dumped into our water supply the way that we treat our water will not kill themThere is a way to treat a Toxoplasmosis Toxoplasma gondii infection but it is difficult3350 of us are already infected with this parasite When women get pregnant often the dormant parasite becomes active o Only in France and Austria is there mandatory Toxo screening for pregnant women o Aside Trichimonas foetus and Trichimonas vaginalis are also problemsThere is only ONE species for Toxoplasmosis o It is part of the phylum Apicomplexa ToxoplasmaDomainEukaryotaKingdomChromalveoataSuperphylumAlveolataPhylumApicomplexaClassCoccidia o Other Coccidian parasitesEimeria species Sarcocystis species Neospora species Cryptosporidium speciesAll Eukaryotes unicellular intracellularOrderEucoccidioridaFamilySarcocystidaeGenusToxoplasmaSpecies ONLY ONET gondiiToxoplasma is a food and water borne pathogen The development of oocytes that are shed with the definitive host cat feces and contaminate the encironment Toxoplasma gondiiA protozoan parasite that was first described in 1908 in Tunis by Nicolle also got the Nobel Prize for typhus and Manceaux in the gundi Ctenodoactylus gundi whch is an African rodent The same year it was described in Brazil by Splendore in rabbitsIn 1909 the organism was named Toxoplasma gondiiSeveral decades passed before the pathogenic role of T gondii in humans was discovered o The first recorded congenital case1923 o The first recorded adult case19401948 Sabin and Feldman serological dye test the standard basis for diagnositic testsBeginning of the 1970s whole parasite life cycle described by Frenkel and Hutchinson Life CycleThe life cycle is very simple compared to other parasitesT gondii can infect any warmblooded vertebrate including cats But important is that most infection is through intermediate hosts this is when the asexual stage of the parasite occurs Intermediate hosts would include humans The definitive host has the sexual stage of the parasite therefore the gametes and the oocysts are in the felines HINT When diagnosing it is important that you would not look in the feces of intermediate hosts to try and find oocysts In intermediate hosts you need to be looking for seropositivity In this case we would be looking for IgM more recent IgG exposed a while ago1 o HOWEVER sometimes when you get infected the IgM can remain in the body for up to 2 years So you can take a blood sample and look for it You can also look for AgIg binding in a blood sampleSo the oocysts are only in cats and the intermediate hosts have 4 sporozoites Most intermediate hosts might have the dormant bradyzoites which may be activated later Intermediate hosts can be infected by cat litter or by meat raw undercooked from other intermediate hosts Infected water is another way When your immune system is down tachyzoites cross the placenta and the baby will get the disease There is even ocular toxoplasmosis and it can also get into the brain ContaminationOccurs mainly by the oral route o 1 Ingestion of raw or partly cooked meat especially pork lamb or venison thatcontains tissue cysts of bradyzoites Handtomouth contact after handing undercooked meat or from using utensils contaminated by raw meat that contains tissue cysts o 2 Ingestion of oocystcontaminated cat feces through handtomouth contactUnwashed vegetables gardenine cleaning a cat litter box contact with child sandboxes touching anything that has come into contact with cat feces o 3 Drinking water that is contaminated with oocysts sporozoites o 4 Transplacental infection in utero tachyzoites o 5 Transplantation of an infected organ bradyzoites in tissue cysts or blood transfusion tachyzoites rare T gondii is a major zoonotic pathogenThere is a huge reservoir in intermediate hostsPrevalence in humans o 30 of the human population is seropositive o Up to 60 in Quebec especially Nunavilk Inuit Nunavut Western Europe o Depends mostly on nutritional habits where undercooked meat is traditionally eaten and on contact with catsPrevalence in animals o 10 in pork 40 in sheeplamb and 2063 in goats Quebec 2000 Toxoplasmosis is usually benignAn average of 30 of the population is seropositive for Toxoplasma but very few have developed clinical symptoms because the immune response is usually very efficiento First line of defense is the innate immune system neutrophils DCs macrophages These become activated release IL12 IFNgamma and try to get rid of the infection there o But the parasite interacts with the immune system in order to surviveAcute toxoplasmosis can be asymptomatic but flulike symptoms are often observed 13 weeks postinfectionThe acute phase virulent tachyzoites fades in a few days to weeks leading to the latent stage of the infection bradyzoite tissue cysts which is normally asymptomatico The parasite does not want to come in and kill you right away this is not very helpful for the parasiteAny nucleated cell can be infected by the tachyzoitesToxoplasmosis is not benign in two cases o 1 In the case of immunocompromised patients HIVAIDS transplant or cancer patients on immunosuppressive therapy toxoplasmosis can develop The most notable manifestation is the toxoplasmic encephalitis which is fatal without drug treatment o 2 If a primary infection with T gondii occurs during pregnancy tachyzoites can cross the placenta possibly leading to hydrocephaly microcephaly intracranial calcification and chorioetinitis with the possibility of miscarriage or intrauterine death Ocular toxoplasmosis may occur later in lifeInfection in the 1st trimester incidence of transplacental infection is low 15 but disease in neonate is most severe 2Infection in the 3rd trimester incidence of transplacental infection is high 65 but infant is usually asymptomatic at birthClinical toxoplasmosis in vulnerable groups common denominatorcompromised immunological mechanisms o 1 AIDS patients symptomatic phase when CD4 T cell count200 cellsmicrolitre due to tissue cyst reactivation toxoplasmic encephalitis TEWhen the bradyzoites are shifted to tachyzoites because it is sensed that the host is lacking IFNgamma or IL12 for exampleWhen there is stressHSP then the tachyzoite will go back to the bradyzoite o 2 Allograft organ recipients immunosuppressive therapy is necessary to tolerate the allograft but high risks of tissue cyst reactivation o 3 Patients on prolonged corticosteroid therapy powerful antiinflammatory drug to suppress inflammatory disorder o 4 Fetus incmpetent immunological mechanisms transplacental transmission of tachyzoites The tachyzoite of T gondii the acuteinvasiveproliferative stage67 micrometers in length 23 micrometers in widthReplicate intracellularly in any nucleated cell T gondii subcellular organellesWhen the parasite invades they will form a parasitophorevacuole so that they are protectedSome stagespecific surface antigens SAG are present so when you want to diagnose it is easy to find something immunogenic in the host o Adhesins SAG1 SAG2 SAG2b SAG3 etc GPIanchored proteins which act as redundant receptors for binding or selfproteoglycans on various host cells Toxoplasma has a complete set of canonical eukaryotic organelles nucleus secretory pathway etc plus TWO endosymbionic organelles mitochondrion apicoplast The parasite contains an apical complex of specialized cytoskeletal elements and secretory organelles micronemes rhoptries Rhoptries and the microneme are secretory vesicles that help to invade host cells It also contains an inner membrane complexReplication is by endodyogeny assembly of two daughter cells within a mother cell therefore they divide in exponential form The bradyzoite of T gondii the dormant chronic stage 3
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