Toxoplasmosis

Toxoplasmosis is caused by the single-celled parasite Toxoplasma (T.) gondii. In the case of an initial infection during pregnancy, the pathogens can be transmitted to the unborn child (connatal infection) and cause severe damage to or death of the unborn child. About half of all toxoplasmosis infections are said to be food-borne.

Occurrence

Infections with T. gondii are common in animals and humans worldwide.

Reservoir

Cats and other felids are the final hosts, in which the sexual reproduction of the parasites can take place. If cats feed on rodents or birds that contain toxoplasma cysts in their tissues, or if they are fed raw meat that contains toxoplasma cysts, the parasites undergo a sexual reproduction cycle and are excreted as oocysts in the faeces.

The range of possible intermediate hosts that can become infected by oocysts includes humans, sheep, goats, rodents, pigs, cattle, chickens and birds.

Mode of transmission

Intermediate hosts, including humans, acquire infection by oral ingestion of oocysts during contact with infected cats, by ingestion of food contaminated with cat faeces, or by oral ingestion of permanent forms (Toxoplasma cysts) in the tissues of an intermediate host (e.g. undercooked sheep meat). If a first-time infection with parasitemia (appearance of parasites in the blood) occurs during pregnancy, toxoplasma can also be transmitted diaplacentally to the unborn child via the blood route.

Incubation period

10-23 days after consumption of cysts in raw meat or 5-20 days after ingestion of oocysts (e.g. through vegetables contaminated with cat faeces).

Symptoms

In healthy adults, infection with T. gondii usually progresses without signs of illness or with unspecific symptoms. In most cases, infections in the first trimester of pregnancy results in the death of the fetus. In the second trimester, hydrocephalus, calcifications in the brain or severe eye damage may occur. In the last trimester, infection usually leads to clinically inconspicuous newborns; late damage can only occur months or years later, in the form of developmental disorders, mental retardation or eye changes, even blindness. In immunocompromised persons (e.g. AIDS), infection can lead to unchecked multiplication of the toxoplasma cysts, with the development of brain toxoplasmosis in the form of encephalitis.

Therapy

Treatment of existing symptoms with medication.

Prevention

Pregnant women who have tested negative for antibodies against toxooplasmosis should avoid contact with new cats (cats that have not been living in the household for a long time and cats whose eating habits cannot be controlled), as well as avoiding undercooked meat and washing vegetables thoroughly before consumption. Wear work gloves when gardening because of the possibility of contact with cat feces.

In Austria, there is no official obligation to report toxoplasmosis. In 2018, the toxoplasmosis screening of the University Department of Paediatrics and Adolescent Medicine of the Medical University of Vienna found 96 pregnant women with infection and treated them antiparasitically. Eight confirmed connatal infections with Toxoplasma gondii were diagnosed.

In the case of livestock and cats, samples from animals are sent to the laboratories for testing for T. gondii only after clinical suspicion, such as after abortions, out of private interest or as part of studies. In 2018, 35 samples from cattle, 21 from sheep and 30 samples from goats were handed in for serological testing. Antibodies against toxoplasma were present in five samples from cattle, 11 from sheep and 19 from goats; the pathogen was not directly detectable in any sample (four samples from cattle, 23 from sheep and 15 from goats).

In Austria there is no official obligation to report toxoplasmosis. The toxoplasmosis laboratory of the Department of Paediatrics and Adolescent Medicine of the Medical University of Vienna processes amniotic fluid samples for PCR analysis from the Austrian prenatal centres. Umbilical cord blood from children of infected pregnant women is also examined throughout Austria in the interests of quality control. This allows a follow-up of children of infected mothers and a survey of the infection status of the children.

Diagnostics

Serological antibody detection from blood samples is the primary routine method for diagnosis. In addition to indirect pathogen detection, direct microscopic detection methods and nucleic acid detection by polymerase chain reaction (PCR) are also available for amniotic fluid, spinal fluid, bronchial lavage, eye chamber fluid or placenta material.