Failure of intertypic recombinant constructed from HSV-1 × HSV-2 virulent parents to induce ocular pathology

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Abstract
An intertypic recombinant constructed from HSV-1 × HSV-2 parents was isolated which failed to induce any overt ocular pathology when inoculated onto the sacrificed cornea of four-week-old SJL/J mice. During the 24-48 hour post-infection period there was transient virus replication but by day 3 the infectious titer in the eye had dropped by ≥ 104-fold, and little or no virus could be recovered thereafter. When immunosuppressed (600 r) mice were infected corneally, virus clearance was delayed several days but again no obvious ocular pathology was seen, and no mice died. By contrast, infection of the cornea with either parent was followed by virus replication and development of clinically apparent pathology which could progress to blinding stromal keratitis. The genome of the intertypic recombinant was analyzed by agarose gel electrophoresis of restriction endonuclease digests and found to consist entirely of HSV-1 DNA except for HSV-2 DNA sequences located between map units 0.10 – 0.16, 0.41 – 0.43, and 0.77 – 1.0. Potential explanations for the loss of virulence are discussed.