What is the role of toxoplasma retinochoroiditis in the ocular manifestations of HIV infection?

Updated: Jul 21, 2021
  • Author: Luca Rosignoli, MD; Chief Editor: Andrew A Dahl, MD, FACS  more...
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Toxoplasmosis is the most common cause of chorioretinitis, accounting for about 30-50% of all posterior uveitis cases. Ocular manifestation usually follows systemic disease.

Infection with T gondii may be congenital, but most cases are acquired later in life. T gondii is an intestinal parasite in cats. The organism usually forms cysts that contain many organisms. The cysts may exist in 1 of 3 forms: (1) oocysts, in cat feces; (2) tachyzoites, proliferative form; and (3) bradyzoites, encysted form. Infection in humans may occur either by inhalation or by consuming poorly cooked meat or unpasteurized milk that has been infested with the organism.

T gondii may remain as bradyzoites within an inactive chorioretinal scar until reactivated as a result of immunosuppression. The exact mechanism of reactivation has not been elucidated completely. However, it is the transformation of the bradyzoites into tachyzoites that allows for new infection of the retina and choroid, leading to recurrent chorioretinitis. In HIV-positive cases of toxoplasma chorioretinitis, brain imaging should be considered to rule out concurrent central nervous system involvement.

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