- Toxoplasma gondii – a protozoan – occurs worldwide in mammals and birds. Asymptomatic infection in humans is common.
- The main host in Australia is the domestic cat, which become infected mainly through eating small infected mammals, including rodents and birds.
- Acute toxoplasmosis in pregnant women can affect the unborn child.
- Adults most commonly become infected after by eating raw or undercooked meat infected with T. gondii tissue cysts.
Notification requirement for toxoplasmosis
Notification is not required.
Primary school and children’s services centres exclusion for toxoplasmosis
Exclusion is not required.
Infectious agent of toxoplasmosis
Toxoplasma gondii is the protozoan that causes disease.
Identification of toxoplasmosis
Toxoplasmosis is asymptomatic in 80 per cent of cases. The most common sign in symptomatic patients is enlarged lymph nodes, especially around the neck. The illness may mimic glandular fever, with other symptoms of muscle pain, intermittent fever and malaise.
Dormant infection persists for life and can reactivate in the immunosuppressed person. These patients are at risk of serious disease, with brain, heart or eye involvement, pneumonia and occasionally death.
Cerebral toxoplasmosis or chorioretinitis may complicate AIDS, typically when the lymphocyte CD4 cell count drops below 100 per cubic millimetre.
Acute toxoplasmosis in pregnant women can affect the unborn child. In early pregnancy, brain damage, and disorders of the liver, spleen and eye may occur. Infection in late pregnancy may result in persistent eye infection through life. Toxoplasmosis acquired after birth usually results in no symptoms or mild illness.
Infection may be diagnosed by visualisation of the protozoa in biopsy material, serology or polymerase chain reaction (PCR) testing.
Serological results require careful interpretation, and should preferably be performed and discussed with a reference laboratory. In general, Toxoplasma-specific IgG antibody appears 2–3 weeks after acute infection, peaks in 6–8 weeks and often persists lifelong.
Presence of Toxoplasma-specific IgM antibody suggests infection within the past 2 years. False-positive IgM results are common, and the tests should always be repeated before final interpretation. False-positive results are particularly common in autoimmune disease.
Presence of IgA antibodies is said to correlate with acute infection.
Testing paired sera taken 2 weeks apart is often helpful, as is IgG antibody avidity testing.
A specific PCR test performed on amniotic fluid may determine whether a fetus has become infected.
Incubation period of Toxoplasma gondii
The incubation period is uncertain but probably ranges from 5 to 23 days.
Public health significance and occurrence of toxoplasmosis
T. gondii occurs worldwide in mammals and birds. Infection in humans is common, generally without clinical sequelae.
Infections during pregnancy may lead to severe complications for the fetus. Primary or reactivated lesions may lead to severe complications in immunosuppressed patients.
Reservoir for Toxoplasma gondii
The main host in Australia is the domestic cat. Cats acquire the infection mainly through eating small infected mammals, including rodents and birds, and rarely from the ingestion of infected cat faeces. Only young felines harbour the parasite in the intestinal tract, where the sexual stage of the life cycle takes place, resulting in the excretion of oocysts in faeces for 10–20 days.
Many other intermediate hosts, including sheep, goats, rodents, cattle, swine, chicken and birds, may carry an infective stage of T. gondii encysted in their tissues. This occurs more commonly in muscle and brain. Tissue cysts remain viable for long periods.
Mode of transmission of Toxoplasma gondii
Adults most commonly acquire toxoplasmosis by eating raw or undercooked meat infected with tissue cysts. Consumption of contaminated, unpasteurised milk has been implicated. Unfiltered water in developing countries can also be contaminated and cause outbreaks.
Children may become infected by ingestion of oocysts in dirt or sandpit sand after faecal contamination by cats, particularly kittens, or other animals.
The infection may also be transmitted through blood transfusion and organ transplantation. Transplacental transmission may occur when a woman has a primary infection during pregnancy.
Period of communicability of toxoplasmosis
Toxoplasmosis is not transmitted person to person except in utero.
Oocysts excreted by cats sporulate and become infective 1–5 days later. They may remain infective in water or moist soil for more than a year.
Tissue cysts in meat remain infective for as long as the meat is edible and undercooked.
Susceptibility and resistance to toxoplasmosis
Everyone is susceptible to infection. About 75 per cent of women of childbearing age are susceptible to primary infection.
Immunity is thought to be lifelong. However, patients undergoing immunosuppressive therapy – in particular, for haematological malignancies – or patients with AIDS are at high risk of developing illness from reactivated infection.
Control measures for toxoplasmosis
No immunisation is available.
Pregnant women and immunosuppressed people should be advised to:
- cook meat thoroughly (until no longer pink) and avoid uncooked cured meat products
- not consume unpasteurised milk or its products
- wash all raw fruit and vegetables carefully before eating
- wash hands thoroughly before meals and after handling raw meat
- delegate the cleaning of cat litter trays to others wherever possible; if this is not possible, gloves should be worn during cleaning and hands washed well afterwards
- ensure that cat litter trays are emptied daily and regularly disinfected with boiling water to dispose of the oocysts before they become infective.
Cats should only be fed with dry, canned or boiled food, and should be discouraged from hunting and scavenging. However, direct contact with cats is rarely the cause of infection. Cats are generally infected as kittens and only excrete the oocysts for 2 weeks after their initial infection.
Sandpits should be covered when not in use to stop cats defaecating in the pit.
Control of case
Isolation of the patient is not required.
Specific anti-protozoal treatment may be indicated in immunosuppressed people, for infections during pregnancy, or where there is eye or other organ involvement. Specialist advice should be sought. Immunosuppressed people may also require prophylactic treatment for the duration of their immunosuppression, generally with cotrimoxazole therapy.
Infants who acquire an infection before birth may require prolonged treatment to reduce the risk of ongoing active infection.
Control of contacts
Children of mothers with evidence of previous immunity more than 6 months before conception are not at risk. Primary infection in pregnancy is rare, although up to one-third of these infections result in transplacental spread to the developing fetus.
Primary infection in pregnancy can cause serious fetal disease. Infection in the first trimester results in a low fetal infection rate (15 per cent) but a higher risk of serious disease. Infection later in pregnancy results in a higher infection rate but generally less severe disease.
Diagnosis and treatment during pregnancy appear to reduce the effects on the baby.
False-positive IgM (and less commonly IgG) antibody test results do occur, and treatment should never begin without further testing. Where infection of the mother is confirmed, treatment is indicated.
Amniocentesis with PCR testing can be carried out to determine whether transmission to the fetus has occurred.
Newborns of mothers with primary or active infection during pregnancy are treated empirically until congenital disease is ruled out. Where infection is confirmed, treatment is continued for 12 months to help reduce long-term effects.
Outbreak measures for toxoplasmosis
Reviewed 08 October 2015