Toxoplasmosis

Cause

Toxoplasma gondii, a protozoa.

Description

Cats are the definitive host for this parasite but there are a wide range of intermediate hosts such as livestock, wildlife, birds and people.

Where the disease occurs

Toxoplasmosis is one of the most common infections in the world. Almost one half of the human population will at some time become infected, but most will not be adversely affected.

The disease in animals

Cats, both wild and domestic, are the only definitive hosts for Toxoplasma gondii. This means that the parasite can only produce oocysts (eggs) when infecting a cat. These oocysts are excreted in great numbers in the cat's faeces. Oocysts are very resistant and may survive in the environment for well over a year.

Other animals and people, are intermediate hosts of Toxoplasma gondii. These hosts can become infected but do not produce oocysts. The infection results in formation of tissue cysts in various tissues of the body.

Most cats infected with T.gondii will not show any signs of disease. Other animals can show various signs of disease, abortion, weak newborn, respiratory problems and occasionally nervous signs. Deaths can occur.

Control of disease in animals

Cats should be controlled and kept away from animal and human food.

How people can get the disease

The parasite occurs everywhere but clinical disease is uncommon. Most cases go undiagnosed as only 10-20% of adults will develop symptoms. Symptoms in people are mild and include: fever, headache, muscle aches and enlarged lymph nodes.  

Infection occurs from exposure to cat faeces or by eating raw or undercooked meat or vegetables that are contaminated with the parasite. It is an occupational risk for veterinarians, farmers and abattoir workers who handle infected animals.

If contracted by a pregnant woman, toxoplasmosis can pose a serious risk to her unborn baby. Up to 90% of infected babies appear normal at birth. However, 80-90% will develop sight-threatening eye infections months to years after birth. Some also develop hearing loss, hydrocephalus (water on the brain), mental retardation, learning disabilities or seizures.

Toxoplasmosis during pregnancy also can result in miscarriage or stillbirth. About 1-10 infected babies have a severe toxoplasma infection evident at birth. Some die within a few days of birth. Those who survive sometimes suffer from mental retardation, severely impaired eyesight, cerebral palsy, seizures and other problems.

Active infection normally occurs only once in a lifetime. If a woman develops immunity to the infection at least 6-9 months before pregnancy, there is rarely any danger of passing it on to her baby.

Pregnant women and their foetuses are most at risk. A form of cerebral disease occurs in people with impaired immune systems such as AIDS patients and organ transplant recipients.

Treatments for people

Treatment is usually not necessary but may be undertaken in pregnant women. Cerebral toxoplasmosis cases can be treated with appropriate antibiotic therapy.

Preventing the disease in people
  • Pregnant women should avoid cats and should not empty litter containers.
  • Pregnant women should avoid lambing ewes.
  • Undercooked meats and raw vegetables and water supplies potentially contaminated with cat faeces should be avoided.
  • Cook meat well and wash vegetables before eating.
  • Wash your hands after contact with cats or potentially contaminated material (i.e. soil).
  • Wear gloves whilst gardening.
  • Feed commercial/formulated food to cats or well cooked meats.

Further information

Last updated 27 September 2012