Toxoplasmosis

Toxoplasmosis is caused by infection with Toxoplasma gondii, a parasite that infects up to 60% per cent of the population in some places. It is related to the parasites that cause malaria and cryptosporidiosis, two other globally significant illnesses.

Humans become infected with Toxoplasma through contact with parasites shed into the environment from infected cat faeces, or by eating raw infected meat. In most people, the initial infection causes mild, or no, symptoms.

In people with weakened immune systems, toxoplasmosis can lead to:

• Brain damage, including encephalitis (inflammation), which can cause confusion and loss of coordination
• Eye damage, impairing vision. Toxoplasmosis is a leading cause of blindness in some communities
• Lung infections
• Coma and death

Pregnant women with toxoplasmosis can transmit the parasite through the placenta to their foetus. This can cause problems including:

• Premature birth
• Brain damage, potentially causing abnormal brain size, seizures and intellectual disability
• Eye damage, potentially causing blindness
• Ear damage, causing hearing loss

Often these symptoms do not become apparent in the child until a decade or more after birth.

As well as causing an immediate ‘acute’ infection, Toxoplasma parasites can form cysts in the infected person’s muscles, heart, brain and eyes. These cysts are found in an estimate of 25 to 30 per cent of people world wide. The parasite can lie dormant in cysts for years. If a person’s immune system is later weakened, the parasite can emerge to cause severe toxoplasmosis.

Re-emergence of a dormant Toxoplasma infection is a significant cause of illness and death in people infected with HIV.

Chronic infection with Toxoplasma has been associated with mental disorders such as schizophrenia and bipolar disorder. It has recently been suggested that chronic infection of Toxoplasma in the brain might exacerbate symptoms in these conditions due to changes in neurotransmitter pathways.

Most people infected with Toxoplasma do not require any treatment. People with compromised immunity, and pregnant women, can be treated with anti-parasitic medications.

Toxoplasma infections can be reduced in people with HIV by treating with antiretroviral medications, which slow the loss of immune function.

Toxoplasma is a parasite that is closely related to Plasmodium, which causes malaria. Many of the genes and proteins that are used by Toxoplasma to infect cells are similar to those used by Plasmodium.

Research into Toxoplasma can provide insights into processes that are also used by Plasmodium. Toxoplasma is easier to work with in the laboratory than Plasmodium because:

• Toxoplasma is more easily grown in the laboratory.
• It is easier to manipulate or disrupt genes in Toxoplasma than in Plasmodium.