Acquired retinochoroiditis in hamsters inoculated with ME 49 strain Toxoplasma

These studies were undertaken to establish an animal model for use in studies of ocular toxoplasmosis. An animal model is needed to examine the development, progression, and resolution of ocular Toxoplasma infections and to study the effects on the disease of currently used and experimental therapies. Cysts of the ME 49 strain of Toxoplasma gondii were injected intraperitoneally into each of 60 golden hamsters. The hamsters' eyes were examined before inoculation and at intervals after inoculation, and fundus photographs were taken. Histologic sections were analyzed and photographed to document the ocular effects of the infection. Retinochoroiditis was found in both eyes of all hamsters within 2 to 3 weeks of inoculation. The disease resolved spontaneously without treatment and was quiescent in most cases at 12 weeks after inoculation. The animals remained in good general health, and those tested had high antibody titers to Toxoplasma (1:256 to 1:32,000) at 6 months after the infection. The discovery of cysts and lesions in the retina confirmed the diagnosis. Although the lesions were not identical to those of human disease, this animal model of ocular toxoplasmosis offers several advantages: reproducibility, short incubation time, spontaneous resolution without treatment, consistent production of cysts, and ease of inoculation intraperitoneally without intraocular injection.