Download The significance of Medical Parasitology

Protozoan 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
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
10
Denmark
27
2
8
4
Italy
12.5
3
0.5
12.5
Norway
19
3
21
3
Switz.
8
13
10
5
Adapted from Sukthana, 2006
Seropositivity rates
Continents and countries
Seropositivity (%)
Europe
Spain
Austria
France
Norway
UK
Poland
28.6%
43%
up to 75%
10.9%
57-93%
46.4-58.5%
USA
16-40%
Central and South America
Costa Rica
Argentina
76%
72%
S.E. Asia
Indonesia
Thailand
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)
•
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
Intra-uterine
infections
•
Immunosuppression,
malignancy, AIDS,
organ transplantation
•
Neurological
complications meningoencephalitis
or cerebral mass
lesions : cerebral
toxoplasmosis
•
Headache, confusion,
ataxia, hemiparesis,
retinochoroiditis
•
Endogenous versus
exogenous infection
Toxoplasma in the
immunocompromised
host
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)
• 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
Prevention
and control
Program for mass screening and prophylactic
treatment of pregnant women for T. gondii
Test 1
Test 2
Test 3
Group
IgG +ve
IgM -ve
No test
No treat
No test
No treat
Infection
before
pregnancy
no risk
IgG +ve
IgM +ve
Repeat IgG
after 3 wks
Treat if high
or rising
IgG -ve
IgM -ve
Treat if IgG
+ve
Possible
infection
soon after
conception
slight risk
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 residance
45
40
35
30
25
Seroprev %
20
15
10
5
0
L
W
K
M
D
D
Toxoplasma gondii and
Schizophrenia
E. Fuller Torrey & Robert H.
Yolken (2003)
Emerging Infectious Diseases 9
(11) 1375-1380