Chad Kumm 5/14/10

The parasite Toxoplasma gondii is a protozoan parasite of the phylum Apicomplexa. The parasite has an indirect life cycle in which members of the Felidae family are the definitive host. This parasite is very successful in terms of its propagation given that it can infect all types of cells in any warm blooded mammal. The most interesting aspect of this parasite however is the fact that it increases reproductive success by altering the behavior of certain intermediate hosts such as rodents. Moreover, evidence is now showing behavioral modifications in humans.

 Estimated 30-60% of the worlds population is infected  Ingestion of any parasitic stage results in toxoplasmosis  The parasite can also be transmitted congenitally or through blood transfusion  Ingestion of tissue cysts in undercooked meat is the primary mode of transmission in humans (after animals ingest oocysts) MMMMM PARASITE

INFO  Trachyzoites preferentially invade tissue of the central nervous system  With their unique glidosome and apex structure, trachyzoites are able to cross the blood brain barrier and force their way into cells  Although T. gondii invades most brain structures, slight tropism is observed in that the amygdala normally has a higher density of cysts in infected individuals SLIGHT TROPISM Amygdala

 The amygdala is an important structure involved in fear pathways/fear conditioning  Experiments show that infection changes fear of cat pheromone in rodents to an attraction in a highly specific manner  Elimination of fear is associated with destruction of specific dendritic arbor in the amygdala  Attraction to pheromone is thought to be associated with the activation of reward pathways via diffusible secretions

Trachyzoites invade CNS cells Next trachyzoites form cysts that are protected from the immune system Cysts are closely associated with Mitochondria the ER and Golgi for nutrient acquisition and active secretion of diffusible substances Cell

SYNTHESIS  Parasite synthesizes and secretes tyrosine  Tyrosine hydroxylase catalyzes the formation of L-Dopa  L –amino acid decarboxylase then catalyzes the formation of Dopamine  Dopamine is a neural transmitter associated with reward and pleasure and is likely associated with behavioral alterations in infected individuals Tyrosine L-Dopa Dopamine Tyrosine Hydroxylase L-amino acid Decarboxylase