What is toxoplasmosis?

Toxoplasmosis is a parasitic infection caused by Toxoplasma gondii. Humans can be infected by coming into contact with infected animal stools (faeces), most commonly from cats. Healthy people usually do not have any symptoms. However, if a pregnant woman contracts the infection, it can cause birth defects in her baby.

Causes

Toxoplasmosis is caused by infection with Toxoplasma gondii, a parasite that is commonly spread by cats. This infection affects roughly a third of the world's human population. The degree to which certain populations are affected varies greatly from place to place. People become infected when they ingest cysts in water or contaminated foods, such as meat or raw vegetables, or through direct contact with soil or cat faeces. The infection can lie dormant in healthy individuals, but if their immune system is weakened, it can result in reactivation.

It is rare for women who have previously acquired Toxoplasma gondii to pass the infection on to their unborn baby. It usually only occurs if the mother newly acquires the infection or it reactivates during pregnancy. Toxoplasmosis during pregnancy, especially in the first trimester, can lead to a congenital disease in the baby.

Toxoplasmosis transmission. 

Congenital

Present from birth.

Immune system

The organs and cells involved in protecting the body against infection.

Trimester

One third of a period of time. Often used to describe the three stages of pregnancy, in which each trimester is about three months long.

Risk factors

Risk factors for toxoplasmosis include:

  • Eating raw or undercooked meat;
  • Working with meat;
  • Contact with cat faeces;
  • Eating unwashed raw vegetables;
  • Contact with soil (e.g., through gardening);
  • Drinking untreated or unfiltered water;
  • A weakened immune system, and;
  • Being born to a mother who was infected just before or during pregnancy.

Immune system

The organs and cells involved in protecting the body against infection.

Signs and symptoms

Most people with Toxoplasma gondii infection do not know they have it. Many people have no obvious symptoms. When they do, symptoms include:

  • Flu-like symptoms - including swollen lymph nodes and muscle aches that last for a month or more;
  • Organ damage - in severe cases, damage to the eyes or the brain and other organs can develop, usually in people with weakened immune systems, but sometimes even in healthy individuals;
  • Impaired vision - toxoplasmosis of the eyes (ocular toxoplasmosis) can result in blurred or reduced vision, pain upon exposure to bright light, redness of the eye and tears, and;
  • Nervous system abnormalities - including impaired reaction time, reduced concentration and behavioural changes.

Infants exposed to the infection in the uterus can experience brain damage or death (congenital toxoplasmosis). Many show no symptoms at birth and may develop them later in life.

Congenital

Present from birth.

Immune systems

The organs and cells involved in protecting the body against infection.

Lymph nodes

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Methods for diagnosis

Blood tests

The presence of antibodies to Toxoplasma gondii can be tested for using a blood test, known as serology test. This test can help differentiate between previous infection and an acute infection.

Testing during pregnancy

Testing for Toxoplasma gondii during pregnancy is only recommended for high-risk groups, or when ultrasound reveals abnormalities in the fetus, such as a build-up of fluid on the brain (hydrocephalus), an abnormally small head (microcephaly), or a large liver and spleen (hepatosplenomegally).

Polymerase chain reaction

If a pregnant woman is found to be infected, then polymerase chain reaction (PCR) testing can be performed on the amniotic fluid to check if the fetus is also infected. If the fetus has been infected at 16 weeks or less, or has fluid on the brain, then termination of the pregnancy may be considered due to the high likelihood of severe brain damage and other complications.

Amniotic fluid

The fluid surrounding and protecting the fetus inside the uterus during pregnancy.

Ultrasound

A scan that uses high-frequency soundwaves to produce images of the body’s internal structures.

Types of treatment

Healthy individuals usually do not require treatment. If you have a weakened immune system or severe symptoms, antiparasitic medications can be used to treat the condition.

If you are pregnant, similar medications can be used to treat an acute infection. The duration of medication may be prolonged if the fetus is believed to have been affected.

Immune system

The organs and cells involved in protecting the body against infection.

Potential complications

Ocular toxoplasmosis

Toxoplasmosis of the eye (ocular toxoplasmosis) can result in damage to the lining at the back of the eye (retina) or the layer of major blood vessels behind the retina (choroid). This can result in partial loss of sight, one eye looking in a slightly different direction to the other, clouding of the lens of the eye (cataracts), shrinking of the eye (microphthalmia), and a loss of cells from the optic nerve that causes poor vision (optic atrophy).

Congenital toxoplasmosis

In most cases, babies born with toxoplasmosis develop normally after treatment with medication. However, in some cases, permanent visual or brain damage can occur. In rare cases congenital toxoplasmosis can lead to death.

Cognitive impairment and behavioural changes

In addition to impairing long-term concentration, behavioural changes in people without other symptoms have been noticed as well, and they tend to be polar opposites between men and women. Men with toxoplasmosis become less sociable and less concerned with their appearance, whereas women become more sociable and concerned with their appearance. Dozens of studies have also found a higher prevalence of schizophrenia in people with toxoplasmosis. 

Congenital

Present from birth.

Prognosis

Most healthy individuals with Toxoplasma gondii infection do not have any symptoms. However, in individuals with a weakened immune system, or during pregnancy, the infection can reactivate and cause ongoing symptoms.

Immune system

The organs and cells involved in protecting the body against infection.

Prevention

Infection with Toxoplasma gondii can be prevented by washing your hands after contact with raw meat, cats or soil, not drinking untreated or unfiltered water, by washing vegetables thoroughly, and cooking meat well before eating.

If you have a cat there are several measures you can take. Frequently changing cat litter and wearing gloves when you change the litter tray, washing the tray out with hot water, not putting cat litter in the kitchen, keeping your cat indoors and feeding it only canned or dried commercial food, are all good ways of reducing the risk of transmission. Pregnant women are generally advised not to empty cat litter for the duration of the pregnancy.