A 7-year-old child has had worsening performance in school for the past 4 months from decreased vision. Examination of the right eye shows diffuse punctate inflammation of the cornea and pannus extending as growth of fibrovascular tissue from conjunctiva onto the cornea. Microscopic examination of a corneal scraping shows lymphocytes, plasma cells, neutrophils, and scattered corneal epithelial cells that have cytoplasmic inclusion bodies. Which of the following infectious agents is most likely to produce these findings?