Protist parasite of human importance

Disease : Toxoplasmosis Agent : Toxoplasma gondii

Diverse routes of transmission

Tissue-inhabiting Apicomplexan. Zoonosis. At

risk groups.

Life cycle of Toxoplasma

Toxoplasma life cycle stages

Oocyst

Tachyzoites

Bradyzoites

Bradyzoites within tissue cysts

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

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

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%

Symptomatology : Toxoplasma

• Most infections benign• Rarely severe

– hepatitis, encephalomyelitis, myocarditis

• Few cases of retinochoroiditis which can progress to blindness

• At risk groups (see over)

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

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

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

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

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)

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

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

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

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

Toxoplasma and Schizophrenia

Robert H. Yolken, F.B. Dickerson & E. Fuller Torrey

(2009)Parasite Immunology 31 (11),

706-715

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