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Is ocular toxoplasmosis caused by prenatal or postnatal infection?
  1. RUTH E GILBERT
  1. Department of Epidemiology and Public Health, Institute of Child Health, 30 Guilford Street, London WC1N 1EH
  2. Medical Eye Unit, St Thomas's Hospital, London SE1 7EH
  1. MILES R STANFORD
  1. Department of Epidemiology and Public Health, Institute of Child Health, 30 Guilford Street, London WC1N 1EH
  2. Medical Eye Unit, St Thomas's Hospital, London SE1 7EH
  1. Dr R E Gilbert

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Ocular toxoplasmosis is commonly attributed to prenatally acquired (congenital) infection unless there is clear evidence that infection was acquired postnatally.1-5 We challenge this view by comparing the risks of ocular disease caused by prenatal and postnatal toxoplasmosis. As the history, clinical appearances, and serological findings associated with the two aetiologies are frequently indistinguishable, we summarise the available information on the risks of ocular disease caused by prenatal and postnatal toxoplasmosis. We conclude that there is no evidence to suggest that the majority of cases are the result of prenatal infection. On balance, the available evidence suggests that at least two thirds of ocular toxoplasmosis is caused by postnatal infection. This information is relevant for counselling patients and for the development of strategies to prevent ocular toxoplasmosis.

Natural history of ocular disease caused by prenatal and postnatal toxoplasmosis

Ocular toxoplasmosis is diagnosed in 20–60% of patients with posterior uveitis, most of whom present between 20 and 40 years of age.6-11 Although these reports reflect caseloads at referral clinics, the reported age distributions are similar to a recent population based study in the UK. In an active surveillance study of patients with suspected toxoplasmosis seen by ophthalmologists serving a population of seven million, 84 patients were reported over 18 months.12 Eighty three patients presented aged 10–54 years, with a mean age of 29 years. The incidence of symptomatic ocular toxoplasmosis was 0.4/100 000/year in British born patients and the lifetime risk of disease 18/100 000. Ophthalmologists around the world are faced with similar groups of patients.

AGE AT ONSET OF OCULAR SYMPTOMS AND SIGNS

Age at first occurrence of ocular symptoms is one of the clinical characteristics that might be expected to help distinguish between prenatal and postnatal toxoplasma infection. Evidence from cohort studies of children with prenatal toxoplasmosis show that 20%–80% develop ocular disease, and that the majority of these children have lesions during the first 2 years of …

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