Epidemiological evidence for toxoplasma chorioretinitis as mostly acquired infection

For decades the generally held view among ophthalmologists has been that toxoplasma infections of the retina and choroid were mostly congenitally acquired and that presentation of active disease during adulthood represented a reactivation of the disease. These beliefs were based on calculated and predicted rates of infection—for instance, by Perkins in the late 1960s, who studied records of patients with disease in the London boroughs. However, the advent of AIDS and the high risk of development of toxoplasmic chorioretinitis among other low virulence infections has led to a re-examination of how toxoplasma is acquired in adulthood. Indeed, it would now appear that acquired infection is a commonly accepted route of infection by many countries in Europe and the South American continent where the infection of oocysts is likely from infected meat products. At the most recent ARVO, several new aspects concerning toxoplasma infection were presented during a mini-symposium session. Firstly, it is now considered that seroconversion to toxoplasma antigen probably represents the period of most recent infection and this usually occurs in childhood or early adulthood. Several strains ofToxoplasma gondii exist and their virulence is related to their nuclear genome but precisely how the organism induces cellular immunity is at present something of a puzzle since it appears to evade both the classic MHC class I and II pathways. Interleukin 10 and interleukin 4 appear to be important in protection from the severe effects of disease since mice deficient in these cytokines are more susceptible to severe lethal infection. The most convincing evidence concerning acquired versus congenital routes of infection came from C Gilbert who presented the results of a prospective study of …