Toxoplasmosis is a protozoan parasite that spreads through food or water contaminated with oocysts, infected meat, or contact with oocysts from feline faeces.
Acute infection is usually asymptomatic, and once acquired, parasites remain in human tissues lifelong.
Symptomatic disease can be seen in patients who are immunocompromised with re-activation of latent infection or with acquisition of new infection.
Symptomatic eye disease can be seen in both patients who are immunocompromised and patients who are immunocompetent.
Primary infection during pregnancy is often asymptomatic in the mother, but can result in congenital disease in the fetus.
Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii. Cats are the definitive hosts for the parasite and can excrete millions of oocysts that survive in the environment for months. Humans are intermediate hosts, and become infected by ingesting uncooked meat infected with tissue cysts (bradyzoites), by ingestion of other food or water contaminated with oocysts, or by transplacental spread of tachyzoites. Once bradyzoites or oocysts are ingested, or tachyzoites have spread through the placenta to a fetus, T gondii rapidly travels to tissues and organs where it encysts and remains permanently. Infection in humans is lifelong and often asymptomatic, unless a patient becomes immunosuppressed.
History and exam
Key diagnostic factors
- presence of risk factors
- focal neurological deficit
Other diagnostic factors
- blurry vision
- slurred speech
- unsteady gait
- fetal microcephaly
- fetal intracranial calcification
- fetal hydrocephalus
- fetal intrauterine growth retardation
- exposure during pregnancy
- residence in a high-risk area
- ingestion of undercooked or raw meat
- exposure to cat faeces
- heavy exposure to soil
- ingestion of unwashed unpeeled raw fruits and vegetables
- occupational exposure
1st investigations to order
- anti-Toxoplasma IgG (serum)
- anti-Toxoplasma IgM (serum)
- CT (with intravenous contrast) or MRI of brain
Investigations to consider
- anti-Toxoplasma IgA (serum)
- anti-Toxoplasma IgE (serum)
- Toxoplasma-specific IgG avidity index (serum)
- differential agglutination test (AC/HS)
- polymerase chain reaction (body fluids and tissue)
- IgG or IgM Immunoblot (serum)
- enzyme-linked immunosorbent spot assay
- interferon-gamma release assay
HIV-positive with CD4+ T lymphocyte count <100
seronegative recipients of solid organs from seropositive donors; seropositive recipients of allogeneic haematopoietic stem cell transplant
newborns: confirmed or highly suspected congenital disease
non-pregnant adults and children: confirmed or suspected disease
pregnant: with seroconversion
immunocompromised: following symptomatic disease
Sarah Hochman, MD
Department of Medicine
Division of Infectious Diseases and Immunology
New York University School of Medicine
SH declares that she has no competing interests.
Kami Kim, MD
Professor of Medicine (Infectious Diseases) and Microbiology and Immunology
Albert Einstein College of Medicine
KK is on the advisory board for the Sanford Guide for Antibiotic Therapy. KK is the author of a reference cited in this topic.
Fabrizio Bruschi, MD
Professor of Parasitology
University of Pisa
School of Medicine
FB declares that he has no competing interests.
Srikrishna Nagri, MD
SN declares that he has no competing interests.
George Y. Wu, MD, PhD
Professor of Medicine
University of Connecticut Health Center
GYW is on the medical advisory boards of the following: Gilead Sciences, Bristol-Myers Squibb, AbbVie, and Intercept.
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