Famciclovir and valaciclovir differ in the prevention of herpes simplex virus type 1 latency in mice: a quantitative study

Abstract

Famciclovir (FCV) and valaciclovir (VACV) have previously been shown to be potent inhibitors of herpes simplex virus type 1 (HSV-1) in a murine cutaneous model. In the present study, mice were inoculated in the skin of the left ear pinna with herpes simplex virus (HSV) type 1. Antiviral therapy was started on different days postinoculation (p.i.), terminating at the end of day 10 p.i. The compounds were administered twice daily by oral gavage at 50 mg/kg of body weight/dose. Mice were sampled on day 5 p.i., during the acute phase of the infection, and the titers of infectious virus in the target tissues (ear, brain stem, and trigeminal ganglia) were determined. At 2 to 3 months p.i., the ipsilateral and contralateral trigeminal and cervical dorsal root ganglia were explanted, and four different methods were used to detect latent HSV. The methods were (i) conventional explant culture for 5 days followed by homogenization, (ii) long-term culture (up to 73 days) of whole ganglia, followed by homogenization, (iii) dissociation by enzymatic disaggregation and an infectious center assay, and (iv) in situ hybridization to detect latency-associated transcripts (LATs). The conventional explant culture method was the least sensitive method, while in situ staining for LAT was the most sensitive, and all mice, including those treated from early times with FCV, were shown to be latently infected. Significantly less latent virus was detected by all four methods, however, in ganglia obtained from mice that had been treated with FCV in comparison with the amount detected in ganglia from mice that had been treated with VACV. However, in no case was latency completely eliminated.

FIG. 1

Effect of antiviral therapy on the weight gain of HSV-1-infected mice. The skin of the left ear pinna of all mice was inoculated with 10⁵ PFU of HSV-1. FCV or VACV was administered by oral gavage at 50 mg/kg/dose twice daily. Antiviral therapy commenced on day 1, 2, 3, 4, or 5 p.i., with all treatments terminating on day 10 p.i. Vertical bars represent standard deviations; error bars have been omitted from those points where the error is very small. (A) FCV-treated mice. (B) VACV-treated mice. ○, uninoculated control; •, infected, untreated control; ⊠, days 1 to 10 p.i.; ▵, days 2 to 10 p.i.; ⊞, days 3 to 10 p.i.; ◊+, days 4 to 10 p.i.; ⊕, days 5 to 10 p.i.

FIG. 2

Detection of latently infected neurons in the trigeminal ganglia by in situ hybridization with a DIG-labelled major LAT riboprobe. Mice were killed 6 to 8 weeks p.i., and 5-μm sections of ganglia were tested as described in the text. (A) Infected, untreated control trigeminal ganglia showing punctate, nuclear staining. (B) Uninfected control trigeminal ganglia. (C) FCV-treated (days 1 to 10) trigeminal ganglia. (D) VACV-treated (days 1 to 10) trigeminal ganglia. Magnifications, ×100.