Toxoplasma gondii

1. TOXOPLASMA
NAVAS. V
II SEM Msc. MICROBIOLOGY
DEPARTMENT OF LIFE SCIENCES
UNIVERSITY OF CALICUT
Toxoplasma
gondii

2. INTRODUCTION
 Toxoplasma gondii is a
protozoan, obligate
intracellular parasite
 Cause Toxoplasmosis
 Infects most species of
warm-blooded animals,
including humans.
 Members of the cat family
Felidae- the only known
definitive host for the sexual
stages - the main reservoirs
of infection.
 Alter the behavior in
Rodents- Manipulation
hypothesis ( Decrease the
aversion of rodents towards
cat’s urine)

3. TAXONOMY
 Phylum Apicomplexa
 Class Conoidasida
 Subclass Coccidiasina
 Order Eucoccidiorida
 Suborder Eimeriorina
 Family Sarcocystidae
 Subfamily Toxoplasmatinae
 Genus Toxoplasma

4. STRUCTURE/MORPHOLOGY
 Crescent shaped, pointed anterior, round posterior, 2 by
6 Micrometer
 Conoid: Rotate, tilt, extent
 Rhoptries: Secretory function associated with host cell
penetration
 A Pellicle, apical rings, microneme, micropore,
microtubules, ER, apicoplast( multi-membrane plastid
like organelle)

5. LIFE CYCLE
 The three stages of T. gondii
(i) Tachyzoites (trophozoites): rapidly proliferate and destroy
infected cells during acute infection.
(ii) Bradyzoites: slowly multiply in tissue cysts.
(iii) Sporozoites in oocysts.
 Cats become infected with T. gondii by carnivorism or
by ingestion of oocysts

6. (i) Tachyzoites (trophozoites): rapidly proliferate and destroy infected cells during acute
infection.
(ii) Bradyzoites: slowly multiply in tissue cysts.
(iii) Sporozoites in oocysts.
LIFE CYCLE…

7. LIFE CYCLE…

8. Toxoplasma gondii -
Tachyzoite

9. EPIDEMIOLOGY / TRANSMISSION
 Toxoplasmosis is one of the most common
infections of humans throughout the world(30 –
50% of global population exposed or chronically
infected)
 Infection is more common in warm climates and
at lower altitudes.
 Distribution is probably related to conditions
favoring the sporulation and survival of oocysts.
 Variations in the prevalence of infection between
geographic areas and between population
groups within the same locale are probably due
to differences in exposure.
◦ Eg 1: A high prevalence of infection in France (65 to 85%) has been
related to a preference for eating raw or undercooked meat.
◦ Eg 2: A high prevalence in Central America has been related to the
frequency of stray cats in a climate favoring the survival of oocysts.

10. EPIDEMIOLOGY / TRANSMISSION
 Human infection may be acquired in several
ways:
◦ Ingestion of undercooked infected meat containing T.
gondii cysts
◦ Ingestion of the oocyst from fecally contaminated hands,
food, or water.
◦ Organ transplantation or blood transfusion
◦ Transplacental transmission
◦ Accidental inoculation of tachyzoites
 The two major routes of transmission to humans
are oral and congenital.
 In human, The tachyzoites are pressured by the
host’s immune response to transform into
bradyzoites and form tissue cysts; these cysts may
remain throughout the life of the host
 Clinical disease may appear if the host becomes
immuno suppressed and the cysts rupture,

11. EPIDEMIOLOGY / TRANSMISSION
 The transmission rate from mother to
fetus ranges from 11% in the first
trimester to 90% in the late third
trimester, with an overall transmission
rate is 40 to 50%.

12. CLINICAL SIGNIFICANCE/
PATHOGENECITY
 Toxoplasmosis can be categorized
into four groups:
◦ 1- Acquired in the immunocompetent
patient
◦ 2 - Acquired or reactivated in the
immunodeficient patient
◦ 3 - Congenital
◦ 4 – Ocular
 Methods of diagnosis and their
interpretations may differ for each
clinical category.

13. Acquired in the immunocompetent
patient
 Generally an asymptomatic infection.
 10 to 20% of patients with acute
infection may develop cervical
Lymphadenopathy and/or a flu-like
illness.
 The clinical course is benign and self-
limited
 Symptoms usually resolve within
weeks to months.

14. Acquired or reactivated in the immunodeficient patient
 Immunodeficient patients often have
central nervous system(CNS) disease
but may have myocarditis or
pneumonitis.
 In patients with AIDS, Toxoplasmic
encephalitis is the most common
cause of intracerebral mass lesions
 Toxoplasmosis in immunosuppressive
drugs using patients due to either
newly acquired or reactivated latent

15. Congenital Infection
 Congenital toxoplasmosis results from an
acute primary infection acquired by the
mother during pregnancy.
 The incidence and severity vary with the
trimester during which infection was acquired.
 Treatment of the mother may reduce the
severity of symptoms in the infant, So an
accurate diagnosis is extremely important
 Many infants with subclinical infection at birth
will subsequently develop signs or symptoms
of congenital toxoplasmosis
 Treatment may help prevent subsequent
symptoms.

17. Ocular Infection
 Ocular toxoplasmosis, an important cause of
Chorioretinitis in the United States, may be
the result of congenital or acquired infection
 Congenitally infected patients are often
asymptomatic until the second or third
decade of life
 Lesions develop in the eye presumably due
to cyst rupture and subsequent release of
tachyzoites and bradyzoites.
 Chorioretinitis is characteristically bilateral
in congenital infection but is often
unilateral in individuals with acute acquired
T. gondii infection.

19. DIAGNOSIS
 DIRECT EXAMINATION :
◦ Microscopy
◦ Antigen Detection
◦ Nucleic Acid Detection Techniques
 SEROLOGIC TESTS :
◦ Determination of Immune Status
◦ Diagnosis of Acute Acquired Infections
◦ Diagnosis of Congenital Infection
◦ Diagnosis of Infection in the Newborn

20. DIRECT EXAMINATION
 MICROSCOPY:
 The slides should be air dried,
fixed in methanol, and stained
with Giemsa for microscopic
examination.
 Tachyzoites may be observed
as free organisms or within
host cells such as leukocytes.
 Well preserved tachyzoites
are crescent shaped and stain
well
 Degenerating organisms may
be oval and stain poorly.
 Tissue imprints stained with
Giemsa may reveal T. gondii
cysts.

21. DIRECT EXAMINATION…
 ANTIGEN DETECTION:
 Immunologic methods are used to identify
parasites in tissue sections or tissue cultures
 For detecting tachyzoites in tissue sections
◦ Fluorescein isothiocyanate-labeled antisera
◦ Peroxidase-labeled antisera
 Enzyme immunoassay(EIA) antigen detection
◦ Due to lack sensitivity for human samples it is
not recommended.
 NUCLEIC ACID DETECTION:
◦ Important use of PCR appears to be in the
prenatal diagnosis of congenital toxoplasmosis
◦ PCR of amniotic fluid has been shown to be
more sensitive for the confirmation of fetal
infection

22. SEROLOGIC TESTS
 Many tests are there for the detection of
antibodies to Toxoplasma:
◦ Methylene blue dye test (DT)
◦ Commercial kits for agglutination tests
◦ Indirect fluorescent antibody (IFA) tests
◦ Enzyme immunoassay(EIA)
 The serologic tests, however does not
give a clear idea about the surety of
infection.
 The specificity and sensitivity rates from
time to time, is used to select a
Toxoplasma-specific antibody

23. Determination of Immune Status
 Screening one serum specimen with a sensitive test for IgG antibodies, such as
DT, IFA, or EIA, is sufficient. A negative test result indicates that the patient has
not been infected. A positive result of any degree indicates infection with T. gondii
at some undetermined time.

24. Diagnosis of Acute Acquired
Infections
 If an acute acquired infection is
suspected, the serum is tested for the
presence of Toxoplasma-specific
antibodies
 A negative result in DT, IgG IFA or EIA
excludes the diagnosis of acute
Toxoplasma infection in an
immunocompetent person.
 The presence of typical
Lymphadenopathy, a high DT or IgG
IFA titer (300 IU/ml or 1:1,000), and
the presence of specific IgM are

25. Diagnosis of Congenital Infection
 Diagnosis of congenital toxoplasmosis
involves:
◦ Diagnosing acute infection in a pregnant woman
◦ Demonstrating infection in the fetus
◦ Documenting infection in the newborn infant
 Amniotic fluid PCR is the recommended test
of choice to establish the intrauterine
diagnosis of congenital toxoplasmosis
 If collected, fetal blood should be tested for
Toxoplasma specific IgG, IgM, and IgA
antibodies
 Demonstrating Toxoplasma-specific IgM or
IgA antibodies in fetal serum or isolating the
parasite from fetal leukocytes is a definitive

26. Diagnosis of Infection in the Newborn
 Diagnosis is made through a
combination of serologic testing, parasite
isolation, and nonspecific findings
◦ An attempt should be made to isolate T.
gondii from the placenta, amniotic fluid, and
cord blood
◦ The child’s serum should be tested for total
IgG and IgM antibody levels and
Toxoplasma-specific IgG, IgM, and IgA
antibodies.
◦ A child with suspected congenital
toxoplasmosis should have a thorough
general, neurologic, and ophthalmologic
examination and a computed tomographic

27. Diagnosis of Ocular Infection
 Toxoplasma Chorioretinitis results
from both acute infection and
congenital infection
 In addition to demonstrating IgG
antibody to Toxoplasma in the serum
of a person with compatible eye
lesions, demonstration of the local
production of antibody and detection
of parasite DNA in aqueous humor
have been used to document active
ocular toxoplasmosis

28. TREATMENT
 In general, physicians treat T. gondii infection in
four circumstances:
◦ Pregnant women with acute infection to prevent fetal
infection
◦ Congenitally infected infants
◦ Immunosuppressed persons, usually with reactivated
disease
◦ Acute and recurrent ocular disease
 Drugs also prescribed for preventive or
suppressive treatment in HIV-infected persons
 The currently recommended drugs work primarily
against the actively dividing tachyzoite form of T.
gondii and do not eradicate encysted organisms
(bradyzoites).

29. TREATMENT…
 The most common drug combination used to treat
congenital toxoplasmosis consists of
Pyrimethamine and a Sulfonamide plus Folinic
acid in the form of leucovorin calcium to protect
the bone marrow from the toxic effects of
pyrimethamine.
 Pyrimethamine inhibits dihydrofolate reductase,
which is important in the synthesis of folic acid and
produces a reversible depression of the bone
marrow.
 Sulfonamides inhibit synthesis of dihydrofolic acid,
also important in the synthesis of folic acid.
 After the 18th week, pyrimethamine and
sulfadiazine may be given if fetal infection is
confirmed by amniocentesis or cordocentesis.
 Spiramycin is recommended for pregnant
women with acute toxoplasmosis when fetal

30.  In Immunosuppressed persons with
toxoplasmosis, a regimen of
Pyrimethamine and Sulfadiazine plus
Leucovorin is the preferred treatment
 Clindamycin is a second alternative for
use in combination with pyrimethamine
and leucovorin for those who cannot
tolerate sulfonamides
 Alternative drugs such as Azithromycin,
Clarithromycin, and Dapsone should be
used in combination with another drug,
preferably pyrimethamine
TREATMENT…

31.  Because of relapse occurs after toxoplasmosis in
HIV infected patients, maintenance therapy
(secondary prophylaxis) with pyrimethamine plus
sulfadiazine (first choice) or pyrimethamine plus
clindamycin (alternative) is recommended for the
patient
 Persons with ocular disease often suggested
Pyrimethamine and sulfadiazine
 Clindamycin, in combination with other
antiparasitic medications, is also frequently
prescribed for ocular disease
 Atovaquone,Rifabutin, Trovafloxacin,
Azithromycin, and Clarithromycin are newer
drugs
 Leucovorin is given with all regimens including
pyrimethamine to avoid potential toxicity.
TREATMENT…

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