Toxoplasmosis (toxo) is an infection caused by a single-celled parasite called Toxoplasma gondii. The parasite infects most genera of warm-blooded animals, including humans, but the primary host is the felid (cat) family. Up to one third of the world's human population is estimated to carry a Toxoplasma infection. Cats are the primary source of infection to human hosts, although contact with raw meat, especially pork, is a more significant source of human infections in some countries.


In humans the disease takes the following forms:


  • congenital toxoplasmosis (passed from infected mother to unborn child) - this may have serious consequences.
  • occular toxoplasmosis (also called retinochoroiditis, which usually results from congenital infection but some symptoms may not occur until age 20 to 40).
  • acute toxoplasmosis in an otherwise healthy person.
  • acute toxoplasmosis in an immunocompromised individual, eg person with AIDS, cancer or treated with immunosuppressing medicines.


Congenital toxoplasmosis is a special form in which an unborn child is infected via the placenta.


A positive antibody titer indicates previous exposure and immunity and largely ensures the unborn baby's safety. A simple blood draw at the first pre-natal doctor visit can determine whether or not the woman has had previous exposure and therefore whether or not she is at risk. If a woman receives her first exposure to toxoplasmosis while pregnant, the baby is at particular risk.


A woman with no previous exposure should avoid handling raw meat, exposure to cat feces, and gardening (cat feces are common in garden soil). However, while risks can be minimized, they cannot be eliminated. For pregnant women with negative antibody titer, indicating no previous exposure to T. gondii, as frequent as monthly serology testing is advisable as treatment during pregnancy for those women exposed to T. gondii for the first time decreases dramatically the risk of passing the parasite to the fetus.


Acute toxoplasmosis During acute toxoplasmosis, symptoms are often influenza-like: swollen lymph nodes, or muscle aches and pains that last for a month or more. Rarely, a patient with a fully functioning immune system may develop eye damage from toxoplasmosis. Young children and immunocompromised patients, such as those with HIV/AIDS, those taking certain types of chemotherapy, or those who have recently received an organ transplant, may develop severe toxoplasmosis.


This can cause damage to the brain (encephalitis) or the eyes (necrotizing retinochoroiditis). Infants infected via placental transmission may be born with either of these problems, or with nasal malformations, although these complications are rare in newborns. Swollen lymph nodes are more commonly found in the neck followed by axillae and then groin. Swelling may occur at different times after the initial infection, persist, and/or recur for various times independently of antiparasitic treatment. It is usually found at single sites in adults, but in children multiple sites may be more common.

Latent toxoplasmosis It is easy for a host to become infected with Toxoplasma gondii and develop toxoplasmosis without knowing it. In most immunocompetent patients, the infection enters a latent phase, during which only bradyzoites are present, forming cysts in nervous and muscle tissue. Most infants who are infected while in the womb have no symptoms at birth but may develop symptoms later in life.


Cutaneous toxoplasmosis While rare, skin lesions may occur in the acquired form of the disease, including roseola and erythema multiforme-like eruptions, prurigo-like nodules, urticaria, and maculopapular lesions. Newborns may have punctate macules, ecchymoses, or “blueberry muffin” lesions. Diagnosis of cutaneous toxoplasmosis is based on the tachyzoite form of T. gondii being found in the epidermis.

Possible link to psychiatric disorders Studies have been conducted that show the toxoplasmosis parasite may affect behavior and may present as or be a causative or contributory factor in various psychiatric disorders such as depression, anxiety and schizophrenia.


Toxoplasmosis is usually caught from cats – the only animal in which the parasite can mature and sexually reproduce. The parasite lives in the cat's bowel and its eggs are discharged with the cat's faeces. They mature and become infectious after approximately one day and can be contagious for several months.


Humans and many kinds of animals are in danger of being infected. After the parasite has entered the body, it's absorbed by the bowel and the organism is carried through the blood. The parasites are finally encapsulated in tissues as so-called tissue cysts. Dormant cysts may become activated and cause illness in the host when they become immunocompromised.


  • Failing to wash one's hands after handling cat litter may cause an infection.
  • Children who eat soil contaminated with faeces are at risk.
  • Eating undercooked meat from infected animals.
  • Blood transfusions (rare).
  • Congenital infection.  


Once the diagnosis of toxoplasmosis is confirmed, you and your doctor should discuss whether treatment is necessary. In an otherwise healthy person who is not pregnant, treatment is not needed. Symptoms will usually go away within a few weeks. For pregnant women or people who have weakened immune systems, drugs are available to treat the parasite that causes toxoplasmosis.

Combination therapy is usually given with folinic acid supplements to reduce incidence of thrombocytopaenia.

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