Direct genotype analysis of Toxoplasma gondii in ocular samples from patients with active rtinochoroiditis

Toxoplasma gondii (T. gondii) is one of the most common protozoan parasites distributed worldwide. This parasite causes different clinical manifestations including ocular toxoplasmosis, which presents as chorioretinitis, vision impairment, and even blindness. Accurate determination of the different genotypes of T. gondii contributing to various infection types is of great importance, especially in cases of ocular infection. This study aimed to determine the genotypes of Toxoplasma parasite isolated for the first time from the eyes of patients with ocular toxoplasmosis in Iran.

A total of 44 aqueous humor and/or vitreous fluid samples were collected in hospital operating rooms from patients with ocular toxoplasmosis and used for genotype analysis. After genomic DNA extraction, two regions at the 5' and 3' ends of the Toxoplasma SAG2 gene were amplified and digested by the restriction endonucleases Sau3aI and HhaI, respectively.

Amplification of the SAG2 locus was successful in 38 samples. Nested PCR of the 5' and 3' ends of this locus produced fragments of approximately 242 bp and 222 bp, respectively. According to the target restriction maps, 37 samples (97.37%) were identified as type I, and one sample was type II (2.63%).

This study is the first report of direct genotyping of intra-ocular fluid specimens from Iranian patients with OT that revealed a striking predominance of T. gondii type I. These findings indicate the potential role of this highly virulent lineage of the parasite in severe ocular disease in Iran, and suggest that appropriate management and control strategies may be required in this population.