Toxoplasma gondii

The only known definitive hosts for Toxoplasma gondii are members of family Felidae (domestic cats and their relatives). Unsporulated oocysts are shed in the cat’s feces and these take 1-5 days to sporulate in the environment and become infectious. Intermediate hosts in nature (including birds and rodents) become infected after ingesting soil, water, or plant material contaminated with oocysts. Cats become infected after consuming intermediate hosts harboring tissue cysts. Humans can become infected by any of the following routes:

• Eating undercooked meat of animals harboring tissue cysts
• Consuming food or water contaminated with cat feces or by contaminated environmental samples (such as fecal contaminated soil or changing the litter box of a pet cat)
• Blood transfusion or organ transplantation
• Transplacentally from mother to fetus

Congenital toxoplasmosis is a group of symptoms that occur when a fetus is infected with T. gondii. If a mother becomes infected while pregnant, the parasite can spread to a developing fetus across the placenta. The risk of congenital disease is lowest (10 – 25%) when maternal infection occurs during the first trimester and highest (60 – 90%) when maternal infection occurs during the third trimester. Congenital disease is most severe when infection is acquired in the first trimester. The overall risk of congenital infection from acute T. gondii infection during pregnancy ranges from approximately 20 – 50%.