Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | Additional sources of information

Victorian statutory requirement

Notification and school exclusion are not required.

Infectious agent

Toxoplasma gondii is a protozoal disease.

Identification

Clinical features
Toxoplasmosis infection is asymptomatic in 80% of people. 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.

More serious disease can develop or reactivate in immunosuppressed patients with brain, heart or eye involvement, pneumonia and occasionally death.

Cerebral toxoplasmosis or chorioretinitis are frequent complications of AIDS when the lymphocyte CD4 cell count drops below 100 / cu mm.

Acute toxoplasmosis in pregnant women can affect the unborn child. In early pregnancy brain damage as well as liver, spleen and eye disorders may occur. Infection in late pregnancy may result in persistent eye infection through life. Toxoplasmosis acquired after birth usually results in no symptoms or only a mild illness.

Method of diagnosis
Infection may be diagnosed by visualisation of the protozoa in biopsy material or serology.

Serological results require careful interpretation and should preferably be performed and discussed with a reference laboratory. In general, toxoplasma-specific IgG antibody appears two to three weeks after acute infection, peaks in six to eight weeks and often persists lifelong.

Presence of toxoplasma-specific IgM antibody suggests infection within the last two years. False positive IgM results are common and should always be repeated before final interpretation. They are common in autoimmune disease.

Presence of IgA antibodies is said to correlate with acute infection.

Testing paired sera taken two weeks apart is often helpful as is IgG antibody avidity testing.

A specific PCR performed on amniotic fluid may determine if a foetus has become infected.

Incubation period

The incubation period is uncertain but probably ranges from 5–23 days.

Public health significance & occurrence

Toxoplasmosis occurs worldwide in mammals and birds. Infection in humans is common.

Infections during pregnancy may lead to severe complications for the foetus. Primary or reactivated lesions may lead to severe complications in immunosuppressed patients.

Reservoir

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 harbor 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

Adults most commonly acquire toxoplasmosis by eating raw or undercooked meat infected with tissue cysts. Consumption of contaminated, unpasteurised milk has also been implicated.

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

Toxoplasmosis is not transmitted from person to person spread except in-utero.

Oocysts spread by cats sporulate and become infective one to five days later. They may remain infective in water or moist soil for over a year.

Tissue cysts in meat remain infective for as long as the meat is edible and under-cooked.

Susceptibility & resistance

Everyone is susceptible to infection. About 75% of women of childbearing age are susceptible.

Immunity is thought to be life long 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

Preventive measures
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 and if this is not possible, gloves should be worn during cleaning and hands washed well afterward
• cat litter trays should be 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 two weeks after their original infection.

Sandpits should be covered when not in use to stop cats defecating in the pit.

Control of case
Isolation of patient is not required.

Specific anti-protozoal treatment may be indicated in immunosuppressed persons, infections during pregnancy, or where there is eye or other organ involvement. Specialist advice should be sought. Immunosuppressed persons may also require prophylactic treatment for the duration of their immunosuppression.

Infants who acquire an infection before birth may require prolonged treatment to reduce the risk of ongoing active infection.

Control of contacts
Not applicable.

Special settings
Pregnancy
Children of mothers with evidence of previous immunity more than six months prior to 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 foetus.

Primary infection in pregnancy can cause serious foetal disease. Infection in the first trimester results in a low foetal infection rate (15%) 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 appears to reduce the effects on the baby.
False positive IgM antibody test (and less commonly IgG) 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 foetus has occurred.

Newborns
Newborns of mothers with primary infection during pregnancy or active infection, and immunosuppressed patients 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

Not applicable.

Additional sources of information

Gilbert, G 2002, ‘Infections in pregnant women’ MJA, vol. 176, pp. 229–236.