Ocular toxoplasmosis past, present and new aspects of an old disease.

Ocular toxoplasmosis (OT) is considered the most frequent form of infectious posterior uveitis and is caused by the protozoan parasite Toxoplasma gondii. The resulting vision loss frequently incapacitates patients and places a considerable socio-economic burden on societies in particular in developing countries. Although, toxoplasmic retinochoroiditis is a world-wide phenomenon stark regional differences with regard to prevalence and presumably route of infection exist. This review will discuss our current clinical understanding of OT including typical and atypical manifestations, patient characteristics which influence the course of disease and treatment options. Even though, congenital and acquired OT are not regarded as separate entities, certain differences exist, which will be assessed and evaluated in detail. A strong focus is laid on the disease causing parasite T. gondii, since solving the mystery of OT aetiology and the development of improved therapies will not be possibly with clinical science alone, but rather requires a precise understanding of parasitological and immunological pathomechanisms. Additionally, the biology and genetics of T. gondii form the foundation for novel and sophisticated diagnostic methods. Scientific advances in the recent years have shed some light on the different role of T. gondii strains with regard to OT manifestation and severity of disease. Genetic and environmental factors influencing OT will be presented and commonalities between OT and toxoplasmic encephalitis will be briefly discussed. Furthermore, the laboratory tools to study OT are crucial in our understanding of OT. In vivo and in vitro experimental approaches will be summarised and evaluated extensively. Finally, a brief outlook is given in which direction OT research should be headed in the future.