Toxoplasma Gondii
last authored: March 2010, David LaPierre
last reviewed:
Introduction
Toxoplasma is an intercellular, protozoan parasite. It can infect all mammals. Most people who become infected remain asymptomatic, though a mononucleosis-like illness can also result.
The Case of...
Epidemiology
Oocytes produce tachyzoites, which then migrate and form cysts of bradyzoites. These cysts can live in muscle, brain and become reactivated to become tachyzoites, where there can chew through tissue.
Over 20% of Americans are IgG positive
Classification and Characteristics
Toxoplasma has three forms in its life cycle.
Sexual reproduction takes place in cats which have eaten tissue cysts. Oocysts contain infective sporozoites, which are produced by the cat ~2 weeks later. Oocysts are infective to humans 1-5 days after elimination.
Once injested by humans, sporozoites invade the intestinal wall, are phagocytised by macrophages, and continue dividing as tachyzoites. Macrophages spread the parasite around the body until an immune response develops 7-10 days later. Once this happens, the parasite forms tissue cysts called bradyzoites.
Tissue cysts can be present for life, in lymph nodes, muscle, brain, retina, myocardium, lungs, and liver.
Transmission and Infection
There are four modes of infection:
- ingestion bradyzoites of undercooked meat. Toxoplasma is found in 8% of beef, 20% of pork, and 20% of lamb.
- fecal-oral contact with cats; may be found in soil
- congenital transmission of tachyzoites
- blood transfusion (very uncommon)
Primary prevention is important in pregnant women. This includes avoiding cat litter boxes, unwashed fruits and vegetables, raw or undercooked meat, and washing knives well.
Clinical Manifesations
Mostly asymptomatic infection. Uncomplicated symptomatic infections can include:
- low-grade fever
- malaise
- headache
- lymphadenopathy
More serious concerns include:
- encephalitis
- myocarditis
- hepatitis
- pneumonia
Infections during pregnancy are usually asymptomatic, though they can cause fetal malformations. These include:
- chorioretinitis
- miscarriage
- mental retardation
- microcephaly
- hydrocephalus
- seizures
Diagnosis
Serology points to infection. IgM becomes positive with days and remains high for 2-3 months, although immunosrbant agglutination assay can lead to a positive IgM for up to 2 years. IgG increases after 1-2 weeks and can remain elevated indefinitely.
Treatment
Treatment to prevent congenital infection is not clear. Spiramycin or pyrimethamine-sulfadizaine may be of benefit.
Resources and References
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