Toxoplasma gondii

Dr.M.Malathi

Obligate intracellular parasite

It belongs to coccidian parasites

The name toxoplasma derived from “toxon” arc or bow ( curved shape of the tachyzoites)

Phylum - sporozoa

Introduction

Three morphological forms

Morphology:

Asexual forms

Tachyzoite

Bradyzoite (Tissue cyst)

Sexual form oocyst

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

TACHYZOITE

Image of a tachyzoite

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

TISSUE CYST:

Image of a tissue cyst:

Sexual form of the parasite found only in cats and felines

OOCYST:

Definitive host

Life cycle

Intermediate host:

Enteric cycle or sexual cycle

Exo enteric cycle or asexual cycle

Life cycle – two phases:

Life cycle

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 transmission5. Laboratory accidents ( Tachyzoites are the infective form in blood)

Transmission to man:

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

CLINICAL HISTORY

CT image :

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

IM NOT RESPONSIBLE FOR MY INFECTION

Features in immunocompetent individual

Features in immunodeficient individual

Congenital toxoplasmosis

Ocular toxoplasmosis

Clinical features:

Congenital toxoplasmosis

Ocular toxoplasmosis:

Direct microscopy Detection of tachyzoites in blood and tissue cyst in tissue biopsy

Staining methods:1. Giemsa2. PAS3. Silver stains4. Immunoperoxidase stain

Diagnosis :

Detection of Toxoplasma antigen by ELISA

Detection of Toxoplasma antibody by1. Sabin feldman dye test2. IgM ELISA3. IgG ELISA4. IgG avidity test

Serology:

Molecular diagnosis

Animal inoculation

Tissue culture

Imaging methods

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

Sabin Feldman dye test

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

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

Diagnosis of congenital toxoplasmosis:

Congenital toxoplasmosis:

oral pyrimethamine (1mg/kg) and sulfadiazine ( 100mg/kg) with folinic acid daily for one year

Treatment:

Toxoplasmosis in AIDS:

Cotrimoxazole Dapsone – PyrimethamineAtovaquone with pyrimethamine

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

Prevention

Time for questions?

Am I causing infection ? OMG

Have you screened me?

THANK YOU……