Problems of herpes simplex virus latency

Effect of topical interferon-beta on recurrence rates in genital herpes: a double-blind, placebo-controlled, randomized study

The aim of this randomized, double-blind placebo-controlled trial was to evaluate the effect of IFN-beta cream applied at the time of recurrent eruptions of genital herpes during 6 months on the overall rate of recurrence. Therapy was initiated at the clinic for the first treated recurrence, and thereafter by the patient for early treatment of eventual subsequent eruptions. Each recurrence was ascertained at the clinic in all 35 evaluable patients. The mean recurrence rate was significantly lower in the group using IFN-beta cream than in the placebo group (p = 0.03). Complete responders without recurrence for the duration of the trial were 36.4% of all patients and 46% among women versus 15.4 and 16.6% in the placebo groups, respectively. A total of 77.3% of all patients were defined as complete or partial responders, their average recurrences/year decreasing from 11 to 2.2 (p < 0.0001). The topical episodic IFN-beta treatment was well tolerated by patients and without side effects. It is concluded that IFN-beta cream application reduces the overall rate of recurrence of genital herpes.

Biology and molecular aspects of herpes simplex and varicella-zoster virus infections

The herpes simplex and varicella-zoster viruses are members of the subfamily alpha herpesviruses with specific properties of the virion and with the capacity to establish latent infections in humans. The genome of each of these viruses has been determined with an estimate of the number of genes and proteins encoded. The biology and molecular events of the herpes simplex virus productive and latent infection have been detailed with the use of both in vitro and in vivo model systems. The neuron is the site of latency in the ganglia with a limited transcription of genes expressed during the latent period. The specific molecular regulation of latency and reactivation are not well established. There are co-cultivation, electron microscopy, and biochemical studies that support the concept of corneal latency, although this has not been proven conclusively. Details about the varicella-zoster virus biology and molecular events are not as well advanced since animal models have been lacking. The biology of the productive infection (varicella) is different from herpes simplex virus infection since the portal of entry is the respiratory system. Data support the concept of the maintenance of latency within satellite cells in the ganglia rather than within neurons. There are multiple genes expressed during this latency. These features may explain the different clinical presentations and course of reactivation (zoster) compared with herpes simplex virus reactivation.

Heterotypic and homotypic re-inoculation of mice already latently infected with herpes simplex virus type 1

Mice were infected at 4 weeks of age with a type 1 strain of herpes simplex virus (HSV) and re-infected 4 weeks later with either a type 1 or a type 2 strain of HSV. The virus used for first infection could be distinguished from that used later since it was resistant to phosphonoformic acid and formed syncytial plaques. Sites used for the second inoculation were as follows: at the site of primary infection, at a different site within the same dermatome or in the equivalent dermatome on the opposite side (also called "remote" site). Re-infection caused no detectable reactivation of the latent PFA resistant virus. After re-infection with a homotypic virus replication of the re-infecting virus was limited to the inoculation site. However after heterotypic re-infection the type 2 strain was occasionally isolated from the ganglia. Previous infection with the PFA resistant type 1 strain clearly reduced the ability of the homotypic or heterotypic strains to establish a latent infection. However, in a few animals ganglia were found to be latently infected with virus from both the first and second inoculations. Analysis of the results suggests that resistance to the establishment of a second latent infection in a ganglion is determined by the general immunity of the animal rather than "immunity" of the latently infected ganglion itself.

Placebo-controlled trial of topical interferon in labial and genital herpes

The efficacy of topical interferon-beta (IFN-beta) treatment was assessed in 25 patients with herpes of the lips or genitals who completed a 2-year follow-up in a double-blind placebo-controlled trial. IFN-beta gel (10(5) U/g) 4 times daily (about 2 x 10(4) U) applied locally during eruptions (about 10 days) reduced the mean number of recurrences (p less than 0.007) and the duration of eruptions (p less than 0.007): in the placebo group these indices did not change significantly. Reduction of symptoms and severity was noted in 11 of 12 patients on IFN-beta and in only 1 on placebo. No important side-effects were recorded. Topical IFN-beta may therefore be advantageous as a time-limited local treatment of recurrent herpes simplex virus infections of the genitals and lips.

Butyrate-induced reversal of herpes simplex virus restriction in neuroblastoma cells

The synthesis of herpes simplex virus (HSV) in mouse neuroblastoma cells (NB, clone 41A3) is restricted. There was a disappearance of infectious virus upon serial passage of infected cells. NB cells treated with sodium-n-butyrate for 24 hr before infection synthesized 200-2000 times more HSV than untreated cells. Infectious center assays demonstrated that the number of cells capable of producing HSV was increased as a result of butyrate pretreatment. Although host protein synthesis was inhibited by HSV infection, viral-induced protein and DNA syntheses were not detected in the absence of butyrate. Cycloheximide blocked the induction of permissiveness by butyrate suggesting that a protein(s) was responsible for allowing HSV synthesis in NB cells. Regulatable host factors involved in HSV replication in neural cells can be studied in the system described.