TISSUE COCCIDIADr. Devika IddawelaDepartment of Parasitology10/11
ObjectivesTo be able to-• Name the Tissue coccidia that cause human disease andstate the habitats of each• State the source (s) of infection, entry to and exit ofagent from humans• Describe the life cycle with stages and events• Identify the stages that cause pathogenic effects• Outline laboratory methods of identification of organism• Identify points in the life cycle where preventive measuresare applicable• Describe the pathogenicity•List the clinical features•Describe transmission, prevention and control of toxoplasmosis
Toxoplasma gondii• Coccidian parasite• Cats ONLY known DEFINITIVEHOST• INTERMEDIATE HOSTS: widespreadin birds & mammals
TOXOPLASMOSISWorld wide distribution; most prevalentparasitic infection of humans-• on serological assays, rates vary incommunities 4-90%Sri Lanka > 50% healthy adults have Ab.Many animals (dogs, cats, rodents arepositive; cats 24% )
•obligate intracellular parasite of all nucleated cells• Latent infection is common• It is an important opportunistic parasite• Causes fatal infections in the immuno-compromisedeg.AIDS
Morphology – There are 3 forms:1. Tachyzoites (endozoites) and pseudocysts–Crescent shape, 4 – 8 µm with single nucleusfound in macrophages (pseudocyst) or anynucleated cell . Multiply rapidly (tachyzoites) .Pseudocysts can cross the placentaCharacteristic form is crescentic shaped trophozoite
2. Bradyzoites ( cystozoites) and true cysts – can befound in any part of the body Organscommonly affected are brain, eye, heart.Cyst wall is by the parasite and host.Zoites in true cysts multiply slowly(bradyzoites)
3.Oocyst – formed in the small intestine ofthe cat and passed in cat faeces. Each sporulatedoocyst contains 02 sporocysts and each sporocyst has04 sporozoitesNOT FOUND IN HUMANS and other intermediate hosts
DefinitivehostLife cycleOnly known definitive hosts for Toxoplasma gondiiare members of family Felidae (domestic cats andtheir relatives)Unsporulated oocysts areshed in the cat’s faecesOocysts take 2-5 days to sporulate in theenvironment and become infective.
Toxoplasma in Definitive host–Gut epithelial cells of catSCHIZOGONY(asexual multiplication)GAMETOGONYmale gametocytesfemale gametocytesZygoteSPOROGONY oocystoutside environment- (sporozoites)
Pathogenesis• Tachyzoites actively invade the cells• Multiply rapidly• Form intracellulaer pseudocyst• This leads to cellular disruption, releasedtachyzoites infect adjacent cells• As the host immunity develops,Tissuetrue cyst form, containing bradyzoitesPeriodic excystation can occur
clinical diseasemajority asymptomaticexcept inNeonatesimmunocompromisedeg. Transplant surgery, AIDS
In Immunodeficient patients- mostlydue to reactivationCommon _ central nervous system(CNS) disease – encephalitisIn patients with AIDS, toxoplasmicencephalitis is the most commoncause of intracerebral mass lesionsbut may have retinochoroiditis,pneumonitis, or other systemic disease.
Ocular toxoplasmosisMost common cause of infectious posterior UveitisDue to• periodic reactivation of congenital toxoplasmosis or• acquired acute infectionClinical features• Floaters• Blurred vision• Usually unilateral• Active lesion is whitish with ill-define margins ( cotton –woolappearance) and pigmented whenquiescentInvolves macular in majority
CONGENITAL TOXOPLASMOSISoccurs generally with acute (1ry) infection inMother –(endometrial reactivation reported))Placental infection Zoites transmittedto foetusRisk of infection increases with durationof pregnancybut foetal damage severe during earlypregnancy- abortion, intra uterine death
diagnosisThe diagnosis of toxoplasmosis istypically made by serologic testing.IndirectDetection ofIgM, IgA or low avidity IgG , rising IgGtitreindicate acute infection,IgG – Past infection
•Use live tachyzoites• live tachyzoites stain blue withalkaline methylene blue dye• If antibodies to T gondii arepresent in the patients serum, theywill damage the organisms• damaged organisms will not takeup the dye and appear as pale"ghosts" compared to undamagedorganisms.• The test needs live tachyzoites and is difficult to perform, soother serological tests are typically used. However, the test isvery sensitive and specific and remains the reference method.Sabin-Felman dye test
Serological test for toxoplasmosis: FATpositive negative
Direct – Demonstration of Parasite1. Observation of parasites in patientspecimens, such as bronchoalveolar lavagematerial from immunocompromised patients,or lymph node biopsy2. Isolation of parasites from blood or otherbody fluids, by intraperitoneal inoculationinto mice or tissue culturemice should be tested for the presence ofToxoplasma organisms in the peritoneal fluid6 to 10 days post inoculation;if no organisms are found – serology 4 -6weeks post innoculation,
• especially in detecting congenital infections inutero. Amniotic Fluid - parasite DNA byPCRPrenatal diagnosis:•Fetal US - calcifications / hydrocephalus•Isolation of parasiteplacenta, amniotic fluid, foetal bloodDetection of parasite genetic material by PCR,
Amniocentesis• Done around 16th week of pregnancy• A long needle is inserted into the Amniotic sac and amniotic fluid is drawn.
TransmissionParasitic stages that can betransmitted to humans• Oocysts• Tachyzoites or pseudocysts• Bradyzoites or true cysts
Transmissiona) oocysts via contaminatedVegetables, fruits and waterFood and water borne
• Accidental ingestion of oocysts after cleaning a cats litter boxwhen the cat has shed Toxoplasma in its faeces• Accidental ingestion of oocysts after touching or ingestinganything that has come into contact with a cats faeces thatcontain Toxoplasma• Accidental ingestion of oocysts in contaminated soil (e.g. notwashing hands after gardening)• Drinking water contaminated with the Toxoplasma oocystsAnimal-to-human (zoonotic) transmission
true cysts (bradyzoites)• eating uncooked or undercooked meat ofinfected animal• Eating food that was contaminatedby knives, utensils, cutting boards,or other foods that had contact withraw, contaminated meat•Organ transplant recipientscan become infected byreceiving an organ from aToxoplasma-positive donor.Rarely•Accidental ingestion ofundercooked, contaminated meatafter handling it and not washinghands thoroughly (Toxoplasmacannot be absorbed through intactskin)
Mother-to-foetus (congenital) transmission• A woman who is newly infected withToxoplasma during pregnancy can pass theinfection to her unborn child (congenitalinfection).Tachyzoites or pseudocysts•Laboratory workers who handleinfected blood can also acquireinfection through accidentalinoculation. • Entering body through abrasions(butchers, veterinarians),• Blood transfusion
PREVENTIONReduce Risk of Toxoplasmosis from Food Avoid eating raw/undercooked meat-15 C for 3 days-65 C 4-5 minutes-4 C persists for monthssalt/nitrates kills cysts,
•Avoid eating raw/undercookedmeats-Wash foods such as green salads leavesand fruits, especially if it is to be eatenuncooked.•Wash cutting boards, dishes, counters,utensils, and hands with hot soapywater after contact with raw meat,poultry, seafood, or unwashed fruits orvegetables.To reduce riskfrom food
Reduce Risk of Toxoplasmosis from theEnvironment• Wear gloves when gardening and during any contactwith soil or sand•Keep outdoor sandboxes covered.• Wash hands after contact with soil
•Feed cats only canned or driedcommercial food or well-cookedfood, not raw or undercookedmeats.••Change the litter box daily .•The Toxoplasma parasite does notbecome infectious until 2 to 5 daysafter it is shed in a cats faecesTo reduce environmentalcontamination
High risk:pregnancy, immunocompromised-•Avoid contact with cats/gardening• Avoid changing cat litter
• Keep cats indoors.• Do not adopt or handle straycats, especially kittens.
SARCOSPORIDIOSIS / SARCOCYSTOSISTwo types - Intestinal sarcocystosisMuscle sarcocystosisOrganism - Sarcocystis spp. many species presentcoccidian parasite, tissue protozoanLife cycle - requires two hosts ; a definitive host & anintermediate hostman can be the definitive host for some species and anintermediate host for some other speciesIn the definitive host - sporogony in intestinal mucosaewith the production of sporocysts (infective stage)In the intermediate host-sarcocysts or Meischer’stubes in muscle (intermediate stage)
Muscle sarcocystosis• Man act as the intermediate host• Definitive host may be a carnivore; monkey, dog• Sarcocysts are found in muscles andconnectivetissues of man• Sarcocysts vary in size from few µm to 5 mm.• These contain cystozoites. Similar to Toxoplasmazoites but larger; banana shaped.Cysts in the muscles can cause myositisand muscle necrosis.
True/ false regarding toxoplasmosisCats act as definitive hostsOocysts could be found in human faecesTrue cysts can be transmitted by blood transfusionTachyzoites can be transmitted by mosquito biteRisk of congenital infection increase with duration ofpregnancyIf the mother get infected during the later part of pregnancy,foetal damage is severKnown to cause life- threatening infections in immuno-compromized patients
Can cause sever disease in pregnancySerology is diagnosis of choiceDetection of IgM indicate a past infectionPrenatal diagnosis is usually rely on serologyWashing hands after going to toilet is goodmethod of preventing infectionOocysts are infective as soon as it pass in thefaeces