Recurrent ocular toxoplasmosis after SARS-CoV-2 infection: three case reports

Ocular toxoplasmosis (OT) is the main cause of infectious posterior uveitis worldwide, that can lead up to complete loss of vision. Since tissue cysts of Toxoplasma gondii persist in the retina following infection, patients with OT have a lifelong risk of reactivation. As SARS-CoV-2 alters the host's immune response during COVID-19, modulating cytokines known to regulate the chronic T. gondii infection, it could potentially trigger the recurrence of OT. In our laboratory, three cases of OT after SARS-CoV-2 infection have been documented over the period of four years (2020-2023), in otherwise immunocompetent adults. The first case of recurrent OT after symptomatic SARS-CoV-2 infection occurred during Delta, and the other two, both asymptomatic, during the peak of the Omicron wave in Serbia. All cases of OT were recurrent, as patients had chorioretinal scarring noted before. T. gondii-specific IgG antibodies of high avidity were detected in all cases, in an absence of specific IgM antibodies. In first case, a 20-year-old female developed symptoms of COVID-19, confirmed by a positive rapid antigen test, five days after the first dose of an mRNA vaccine (BNT162b2). A month later, she experienced blurred vision and photophobia in her left eye, which was discovered to be caused by an active, peripheral chorioretinal lesion. In second case, a 26-year-old female reported having blurred vision and photophobia in the right eye, 1.5 months after a positive rapid antigen SARS-CoV-2 test and asymptomatic COVID-19. Upon examination, an active paramacular lesion was noted in the right eye. In third case, a 26-year-old female developed blurred vision in the right eye, following recurrent focal chorioretinitis. Patient was not vaccinated against SARS-CoV-2 and denied having COVID-19. However, IgG antibodies specific for the receptor-binding domain of SARS-CoV-2 S protein (47.78 BAU/ml) were detected in this sample, indicating a possible recent asymptomatic infection. Having in mind profound consequences of OT, an ophthalmology exam is strongly advised in cases with positive SARS-CoV-2 diagnostic test and known history of OT, regardless of the presence of COVID-19 symptoms.