Protist parasite of human importance
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Protist parasite of human importance
Disease : Toxoplasmosis Agent : Toxoplasma gondii
Diverse routes of transmission
Tissue-inhabiting Apicomplexan. Zoonosis. At
risk groups.
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Life cycle of Toxoplasma
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Toxoplasma life cycle stages
Oocyst
Tachyzoites
Bradyzoites
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Bradyzoites within tissue cysts
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Toxoplasma gondii : Modes of
transmission
• Ingestion of cyst-containing meat (carnivores)
• Ingestion of oocysts (environmental contamination)
• Congenital infection• Transfusion (rare)• Raw goat’s milk,
lambing, transplantation
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Percentage of Toxoplasma infection associated with type of meat consumed
Country Beef (%)
Pork (%)
Lamb (%)
Salami (%)
Belgium 6 2 10 10Denmark 27 2 8 4Italy 12.5 3 0.5 12.5Norway 19 3 21 3Switz. 8 13 10 5
Adapted from Sukthana, 2006
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Seropositivity rates
Continents and countries Seropositivity (%)
EuropeSpainAustriaFranceNorwayUKPoland
28.6%43%up to 75%10.9%57-93%46.4-58.5%
USA 16-40%
Central and South AmericaCosta RicaArgentina
76%72%
S.E. AsiaIndonesiaThailand
58%2.3-21.9%
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Symptomatology : Toxoplasma
• Most infections benign• Rarely severe
– hepatitis, encephalomyelitis, myocarditis
• Few cases of retinochoroiditis which can progress to blindness
• At risk groups (see over)
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Intra-uterine infections
• Severe clinical picture : retinochoroiditis, encephalomyelitis, hydrocephalus, microcephaly
• Most infections result in blindness, severe visual impairment and/or mental retardation
• Estimates 50-70 seriously affected births UK ; approx 3000 congenital cases USA
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Toxoplasma in the immunocompromise
d host
• Immunosuppression, malignancy, AIDS, organ transplantation
• Neurological complications - meningoencephalitis or cerebral mass lesions : cerebral toxoplasmosis
• Headache, confusion, ataxia, hemiparesis, retinochoroiditis
• Endogenous versus exogenous infection
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Cerebral toxoplasmosis : Centre for Disease Control (CDC) criteria for
diagnosis
• Recent onset of focal neurological abnormality consistent with intercranial disease or reduced consciousness
• Evidence from brain imaging of a lesion (CT or MRI)
• Positive serum antibody to T. gondii or response to treatment
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Diagnostic tests for Toxoplasma
• Sabin-Feldman dye test (DT)• Enzyme immunoassay for T. gondii
specific IgM (EIA)• Immunsorbent agglutination assay
(ISAGA)• Enzyme immunoassay for IgG avidity• Isolation and culture of parasite • Direct detection by microscopy and PCR
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Differential Diagnosis
• Immunocompetent adults (DT, IgM EIA)
• Pregnant women (maternal serum DT, IgM EIA, IgG avidity; Amniotic fluid culture or PCR)
• Neonates (DT, EIA, ISAGA for IgM, IgA)
• Organ transplantation (DT, IgM EIA)
• Immunodeficiency (serum and CSF : DT, EIA, ISAGA for IgM and IgA; PCR, culture, microscopy)
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Prevention and control
• Avoid consumption of raw or undercooked meat
• Litterpans should be changed daily
• Wash hands after handling raw meat, litter pans & soil
• Pregnant women should avoid contact with cats
• Issue of prenatal screening
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Program for mass screening and prophylactic treatment of pregnant women for T. gondii
Test 1 Test 2 Test 3 Group
IgG +veIgM -ve
No testNo treat
No testNo treat
Infection before pregnancy no risk
IgG +veIgM +ve
Repeat IgG after 3 wksTreat if high or rising
Possible infection soon after conceptionslight risk
IgG -veIgM -ve
Treat if IgG +ve
Treat if IgG +ve
No previous infection, if seroconver. high risk
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Treatment : toxoplasmosis
• Only accepted treatment pyrimethamine with trisulfapyrimines for 1 month
• Intravenous clindamycin used to treat encephalitis in AIDS patients
• In France spiramycin has been used to treat toxoplasmosis in pregnancy
• Spiramycin is available in the US on a case-by-case basis
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Seroprevalence of Toxoplasmosis by county of
maternal residence
0
5
10
15
20
25
30
35
40
45
L W K M D D
Seroprev %
%
Ferguson et. al. 2009 IMJ
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Toxoplasma and Schizophrenia
Robert H. Yolken, F.B. Dickerson & E. Fuller Torrey
(2009)Parasite Immunology 31 (11),
706-715
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Key points• Individuals with schizophrenia higher
seroprevalence of Toxoplasma• Epidemiology of Toxoplasma and
schizophrenia similar• Antipsychotic drugs inhibit
Toxoplasma• Toxoplasma induces elevated levels
of dopamine• Individuals with schizophrenia higher
exposure to cats