- Clinical science
Toxoplasmosis is a disease caused by the obligate intracellular parasite Toxoplasma gondii. Transmission occurs either through ingestion of cysts found, for example, in raw meat or cat feces, or from mother to fetus through the placenta. The clinical presentation depends on the patient's immune status: In immunocompetent individuals, 90% of cases are harmless and asymptomatic, with the remaining 10% displaying mild mononucleosis-like symptoms. In immunosuppressed patients (e.g., those who are HIV-positive), infection may result in cerebral toxoplasmosis (headache, confusion, focal neurologic deficits) or toxoplasmic chorioretinitis (eye pain, reduced vision). Treatment is indicated for immunosuppressed patients, infected mothers, congenital toxoplasmosis, and immunocompetent patients with more severe symptoms. The treatment of choice is usually a combination of pyrimethamine, sulfadiazine, and leucovorin (folinic acid), with the exception of new infections during pregnancy, which are treated with spiramycin.
For the congenital variant and how to manage infection in pregnant women, see.
- In the US: ∼ 10% of adults
- In some tropical climates: up to 95%
Epidemiological data refers to the US, unless otherwise specified.
- Pathogen: Toxoplasma gondii, an obligate intracellular, single-celled protozoan
Route of transmission
Oral ingestion: The oocytes are excreted in the feces of cats (final host) and are orally ingested by other mammals such as humans, hoofed animals, and birds (intermediate hosts). Primary modes of transmission therefore include:
- Cat feces
- Raw or insufficiently cooked meat
- Unpasteurized milk (especially goat milk)
- Transplacental transmission: see toxoplasmosis during pregnancy
- Via organ transplantation or blood transfusion
- Oral ingestion: The oocytes are excreted in the feces of cats (final host) and are orally ingested by other mammals such as humans, hoofed animals, and birds (intermediate hosts). Primary modes of transmission therefore include:
- Incubation time: 3 days to 3 weeks
- Immunocompetent patients
- (the most common neurological AIDS-defining illness)
- Clinical features (symptomatic usually if CD4 count < 100 cells/μL)
- Toxoplasma tachyzoites and bradyzoites
- Chronic inflammation and necrosis of brain tissue
- Treatment: see “Treatment” below
- Acute toxoplasmosis (current focal infection): yellow-white retinal lesion; , marked vitreous reaction; , concomitant vasculitis; , defects in the visual field at the site of inflammation
- Previous toxoplasmosis (previous focal infection): formation of scars with white atrophic areas and surrounding dark, sharply-defined pigmentation
- Recurrent focal infection usually develops at old scar areas.
- Congenital toxoplasmosis is almost always accompanied by the formation of macular scars and corresponding visual impairment.
- Immunocompetent patients usually do not require treatment.
- First choice
- Spiramycin if maternal infection before the 18th week of pregnancy is suspected/confirmed and infection of the fetus is not suspected/documented (see ) 
- Combination treatment with pyrimethamine, sulfadiazine, and leucovorin (folinic acid) in all other cases
- Duration: minimum of 4–6 week