toxoplasmosis

1. Dr.M.Malathi

2.  Obligate intracellular parasite
 It belongs to coccidian parasites
 The name toxoplasma derived from “toxon”
arc or bow ( curved shape of the tachyzoites)
 Phylum - sporozoa

3. Three morphological forms
Asexual forms
Tachyzoite
Bradyzoite (Tissue
cyst)
Sexual form oocyst

4.  Actively multiplying form
 Crescent shaped
 Seen in acute infection
 Infect all the nucleated mammalian cells
 Inside the host cell, the tachyzoites are
surrounded by a vacuole  asexual
multiplication occurs  rosettes
 Host cell  distends  pseudocyst

7.  Resting stage of the parasite
 Seen in chronic infections  most common
site is muscles and brain
 Inside the cyst  slowly multiplying
trophozoites are called as bradyzoites
 BRADYZOITE:
 Resistant to gastric juice
 Multiplies slowly
 Contains PAS positive amylopectin granules

9.  Sexual form of the parasite found only in cats
and felines

10. Definitive host

11. Intermediate host:

12. Enteric cycle or sexual
cycle
Exo enteric cycle or
asexual cycle

15. 1. Ingestion of sporulated oocysts from
contaminated soil, food or water
2. Ingestion of tissue cyst containing
bradyzoites from undercooked meat
3. By blood transfusion, needle stick injuries,
organ transplantation
4. Transplacentral transmission
5. Laboratory accidents
( Tachyzoites are the infective form in blood)

16.  A known AIDS patient presents with
complaints of fever, seizures, visual defects
and facial nerve palsy and altered sensorium.
 His CD4 count is 78/ul
 CT scan brain shows multiple ring enhancing
lesions in the basal ganglia

18.  A newborn baby is presenting with visual
impairment, microcephaly, hydrocephaly and
on CT scan it showed intracerebral
calcification.

19.  Features in immunocompetent individual
 Features in immunodeficient individual
 Congenital toxoplasmosis
 Ocular toxoplasmosis

22.  Direct microscopy  Detection of
tachyzoites in blood and tissue cyst in tissue
biopsy
 Staining methods:
1. Giemsa
2. PAS
3. Silver stains
4. Immunoperoxidase stain

23.  Detection of Toxoplasma antigen by ELISA
 Detection of Toxoplasma antibody by
1. Sabin feldman dye test
2. IgM ELISA
3. IgG ELISA
4. IgG avidity test

24.  Molecular diagnosis
 Animal inoculation
 Tissue culture
 Imaging methods

25.  Gold standard antibody detection test
 Done only in reference laboratories
 Complement mediated neutralization test
that requires live tachyzoites
 Live tachyzoites are incubated with
complement and test serum
 Alkaline methylene blue dye is added and
reincubated

26.  Toxoplasma antibodies in the serum bind to
the antigens in the live tachyzoites  killed
due to complement mediated lysis
 Killed tachyzoites  thin, distorted and
colourless
 The dilution of the test serum at which 50% of
the tachyzoites are killed  antibody titer of
the test serum

27.  Toxoplasma antigens in amniotic fluid
 PCR
 IgM antibodies in fetal blood by ELISA
 Role of IgG antibodies in diagnosing
congential toxoplasmosis ?
 Ultrasound of fetus at 20 to 24 weeks of
gestation

28.  Congenital toxoplasmosis:
oral pyrimethamine (1mg/kg) and
sulfadiazine ( 100mg/kg) with folinic acid
daily for one year

29.  Toxoplasmosis in AIDS:
Cotrimoxazole
Dapsone – Pyrimethamine
Atovaquone with pyrimethamine

30.  Consumption of cooked meat
 Hand hygiene
 Prenatal and antenatal screening to detect
Toxoplasma infection in women of child
bearing age
 Proper handling of pet cats
 Screening of blood donors and organ donors