Last updated: June 29, 2023

Summarytoggle arrow icon

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 neurological 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 “Toxoplasmosis in pregnancy.”

Epidemiologytoggle arrow icon

  • Prevalence
    • In the US: ∼ 10% of adults
    • In some tropical climates: up to 95%


Epidemiological data refers to the US, unless otherwise specified.

Etiologytoggle arrow icon

  • Pathogen: Toxoplasma gondii, an obligate intracellular, single-celled protozoan
  • Route of transmission
    • Oral ingestion: The oocysts 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 include the following:
      • Cat feces
      • Raw or insufficiently cooked meat (most common)
      • Unpasteurized milk (especially goat milk)
    • Transplacental transmission: see toxoplasmosis in pregnancy
    • Via organ transplantation or blood transfusion


Clinical featurestoggle arrow icon

Diagnosticstoggle arrow icon

Indications for testing may include uveitis or retinochoroiditis with no known history of congenital toxoplasmosis, organ transplantation, and a new diagnosis of HIV. [4][8]

Treatmenttoggle arrow icon

Immunocompetent patients do not usually require treatment.

Cerebral toxoplasmosistoggle arrow icon

Description [5][8][11]

Clinical features [8]

Diagnostics [8][11]

A definitive diagnosis requires the presence of clinical features, biopsy findings of T. gondii, and ≥ 1 mass lesion seen on imaging. Empiric treatment is usually initiated based on typical clinical features and currently available imaging and serology results. [8][11]

Treatment of cerebral toxoplasmosis [13][14]

See “Approach to undifferentiated neurological symptoms in patients with HIV” for initial management of this patient group.

Primary CNS lymphoma is a differential diagnosis of cerebral toxoplasmosis. Until this differential is ruled out, avoid glucocorticoids, as they can alter neuroimaging and biopsy findings and may delay a diagnosis.

Prophylaxis for HIV patients [13]

Acute management checklisttoggle arrow icon

Ocular toxoplasmosistoggle arrow icon

Clinical features [15][16]

Diagnostics [16]

Ocular toxoplasmosis is typically a clinical diagnosis.

  • Fundoscopy
    • Acute toxoplasmosis [18]
      • Yellow-white retinal lesion
      • Marked vitreous reaction: Severe vitritis may result in a "headlight in the fog” appearance.
      • Concomitant vasculitis
    • Previous toxoplasmosis
      • Formation of scars with white atrophic areas
      • Dark, sharply defined retinal pigmentation
  • Adjunctive tests: PCR or antibody titers of ocular fluid if the diagnosis is uncertain

Treatment of ocular toxoplasmosis [16][19][20]

Referencestoggle arrow icon

  1. Parasites - Toxoplasmosis (Toxoplasma infection): Epidemiology & Risk Factors. Updated: March 26, 2015. Accessed: March 13, 2017.
  2. Toxoplasma gondii: from animals to humans. Updated: November 1, 2000. Accessed: March 13, 2017.
  3. Centers for Disease Control and Prevention. CDC Yellow Book 2020. Oxford University Press, USA ; 2019
  4. Robert-Gangneux F, Dardé ML. Epidemiology of and Diagnostic Strategies for Toxoplasmosis. Clin Microbiol Rev. 2012; 25 (2): p.264-296.doi: 10.1128/cmr.05013-11 . | Open in Read by QxMD
  5. Jones JL, Parise ME, Fiore AE. Neglected Parasitic Infections in the United States: Toxoplasmosis. Am J Trop Med Hyg. 2014; 90 (5): p.794-799.doi: 10.4269/ajtmh.13-0722 . | Open in Read by QxMD
  6. Goldman L, Schafer AI. Goldman-Cecil Medicine, 2-Volume Set. Elsevier ; 2019
  7. Furtado J, Smith J, Belfort R, Gattey D, Winthrop K. Toxoplasmosis: A global threat. J Glob Infect Dis. 2011; 3 (3): p.281.doi: 10.4103/0974-777x.83536 . | Open in Read by QxMD
  8. Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents with HIV: 2021 update. Updated: June 22, 2021. Accessed: August 18, 2021.
  9. Reiter-Owona I. Laboratory diagnosis of toxoplasmosis – possibilities and limitations. J Lab Med. 2005; 29 (6): p.439-445.doi: 10.1515/jlm.2005.060 . | Open in Read by QxMD
  10. Konstantinovic N, Guegan H, Stäjner T, Belaz S, Robert-Gangneux F. Treatment of toxoplasmosis: Current options and future perspectives. Food Waterborne Parasitol. 2019; 15: p.e00036.doi: 10.1016/j.fawpar.2019.e00036 . | Open in Read by QxMD
  11. Halonen SK, Weiss LM. Toxoplasmosis. Handb Clin Neurol. 2013: p.125-145.doi: 10.1016/b978-0-444-53490-3.00008-x . | Open in Read by QxMD
  12. Brogi E, Cibas ES. Cytologic Detection of Toxoplasma gondii Tachyzoites in Cerebrospinal Fluid. Am J Clin Pathol. 2000; 114 (6): p.951-955.doi: 10.1309/2xq7-a89r-rdxu-xxg1 . | Open in Read by QxMD
  13. Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents with HIV. Updated: August 18, 2020. Accessed: December 18, 2020.
  14. Vidal JE. HIV-Related Cerebral Toxoplasmosis Revisited: Current Concepts and Controversies of an Old Disease. J Int Assoc Provid AIDS Care. 2019; 18: p.232595821986731.doi: 10.1177/2325958219867315 . | Open in Read by QxMD
  15. Cunningham ET, Margolis TP. Ocular Manifestations of HIV Infection. N Engl J Med. 1998; 339 (4): p.236-244.doi: 10.1056/nejm199807233390406 . | Open in Read by QxMD
  16. Ozgonul C, Besirli CG. Recent Developments in the Diagnosis and Treatment of Ocular Toxoplasmosis. Ophthalmic Res. 2016; 57 (1): p.1-12.doi: 10.1159/000449169 . | Open in Read by QxMD
  17. Eckert GU, Melamed J, Menegaz B. Optic nerve changes in ocular toxoplasmosis. Eye. 2006; 21 (6): p.746-751.doi: 10.1038/sj.eye.6702319 . | Open in Read by QxMD
  18. Aleixo AL, Curi AL, Benchimol EI, Amendoeira MR. Toxoplasmic Retinochoroiditis: Clinical Characteristics and Visual Outcome in a Prospective Study. PLoS Negl Trop Dis. 2016; 10 (5): p.e0004685.doi: 10.1371/journal.pntd.0004685 . | Open in Read by QxMD
  19. Harrell M, Carvounis PE. Current Treatment of Toxoplasma Retinochoroiditis: An Evidence-Based Review. J Ophthalmol. 2014; 2014: p.1-7.doi: 10.1155/2014/273506 . | Open in Read by QxMD
  20. Parasites - Toxoplasmosis (Toxoplasma infection): Resources for Health Professionals. Updated: May 26, 2020. Accessed: March 3, 2021.
  21. Toxoplasmosis in the adult. Updated: February 1, 1974. Accessed: March 13, 2017.

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