1. History
  2. Exam
  3. Photos
  4. Diagnosis
  5. Teaching Points
  6. Comments

Case 137 Teaching Points

  • Toxoplasmosis may be congenital or acquired
  • Acquired toxoplasmosis can result from the following:
    • Ingestion of tissue cysts in undercooked beef, lamb, or pork
    • Ingestion of oocysts
    • Inhalation of oocysts
    • Contaminated blood or tissue products
  • After initial infection, the organism travels via the blood stream to the eye where a focus of infection begins within the retina. This initial infection may be subclinical.
  • The immune response induces the infectious form of the organism called tachyzoites which convert themselves to a cyst form that is extremely resistant to the immune system and results in a chronic latent infection
  • In cases of a subclinical infection, no fundoscopic changes are observed initially. However, if immune function is suppressed, the cyst wall may rupture, releasing organisms into the retina, and a hypersensitivity reaction to Toxoplasma antigens occurs causing a vitritis, anterior uveitis, and papillitis.
  • The retina is the primary site for the multiplying parasites. However, inflammation of the choroid and the sclera may also occur.
  • Involvement of the optic nerve results in optic neuritis or papillitis. This is an important finding as the optic nerve sheath may allow direct spread of Toxoplasma organisms in the brain.
  • Vitritis is often present, severely limiting the details of the fundus. Precipitates of inflammatory cells in the posterior vitreous, thick vitreous strands, and membranes may be present. A vitrectomy may required to remove these.
  • The inflammation that develops in response to Toxoplasma antigens may also cause a granulomatous or non-granulomatous anterior uveitis in addition to vitritis
  • A retinal vasculitis may occur leading to retinal ischemia that may result in neovascularization of the retina and optic nerve

References

Dodds EM. Toxoplasmosis. Curr Opin Ophthalmol 2006;17:557-561.

Chern KC, Zegans ME. Ophthalmology Review Manual, Lippincott Williams & Wilkins: Philadelphia, 2000, pp 262-264.

Last Modified: Wednesday, 28-May-2008 16:15:09 EDT