Toxoplasma gondii

Toxoplasma gondii is an invasive intracellular element in the coccidia. Its occurrence is cosmopolitan, the disease is one of the most common diseases. In the Czech Republic, over 20% of people are positive for specific antibodies.

Transmission
The definitive host is felines. An intermediate host can be any warm-blooded vertebrate (rodent, sheep, cattle or human ). While tissue cysts occur in both types of host organisms, infectious oocysts produced by sexual reproduction of the parasite are found only in the definitive host. The infection is possible:


 * 1) alimentary- foods that are contaminated with oocysts secreted with cat feces - insufficiently heat-treated meat containing tissue cysts
 * 2) transplacentally
 * 3) organ transplants

1. Tachyzoite

 * = pathogenic stage
 * strongly resembles a malarial plasmodium
 * is invasive (enters cells)
 * under certain circumstances it transforms to the bradyzoite stage

2. Bradyzoite

 * they multiply slowly inside the cells without destroying them
 * creates tissue cysts in immune privileged organs ( brain, muscles , eye )
 * infectious stage

3. Oocyst

 * resting infection stage
 * occurs in the intestines of infected cats → is excreted in the faeces (excreted only for a certain time, not for life)
 * contains sporozoites
 * lasts a year or more in the wild

Definitive host



 * 1) the cat becomes infected by ingesting meat containing tissue cysts or food contaminated with oocysts
 * 2) the sporozoite / bradyzoite is converted to tachyzoite
 * 3) tachyzoite attacks enterocytes (it is able to attack any nuclear cell)
 * 4) inside the cell it divides rapidly until the cell is completely filled with tachyzoites
 * 5) the cell bursts
 * 6) tachyzoites are released into the environment and attack other nuclear cells
 * 7) inside the cells, immature oocysts are formed, which are released into the lumen of the intestine during cell breakdown and excreted
 * 8) the immature oocyst matures in a humid environment with air access to the infectious oocyst in 1-5 days

Interhost

 * 1) the intermediate host (human) becomes infected by ingesting meat containing tissue cysts or food contaminated with oocysts
 * 2) the sporozoite / bradyzoite is converted to tachyzoite
 * 3) tachyzoites in its digestive tract pass through the intestinal epithelium and there is a hematogenous spread throughout the body → if it multiplies constantly : acute toxoplasmosis occurs
 * 4) by the reaction of the immune system, the tachyzoite inside the tissue cells changes to the bradyzoite stage
 * 5) the cell changes into an infectious tissue cyst (= cell enlarged, completely filled with bradyzoites) → formation of tissue cysts : latent toxoplasmosis develops

If tachyzoites penetrate the placenta : congenital toxoplamosis develops (followed by fetal harm or miscarriage)

Toxoplasmosis
For more information, see Toxoplasmosis, Congenital Toxoplasmosis .

Related articles

 * Rizikové těhotenství a novorozenec

Reference

 * 1) VOLF, Petr a Petr HORÁK. Paraziti a jejich biologie. 1. vydání. Praha : Triton, 2007. 318 s. s. 103–104.  ISBN 978-80-7387-008-9.