Exacerbation and reactivation of Herpesvirus hominis infection in mice by cyclophosphamide

The effect of alpha blockade on iontophoresis-induced ocular shedding of latent HSV-1 W in different host animals

Previous studies demonstrated that non-specific beta blockade promoted ocular shedding of latent HSV-1 in the mouse and rabbit iontophoresis models. The present study examined the effect of topical alpha blockers, thymoxamine and corynanthine, on reactivation and induced ocular shedding of latent HSV-1 W in different host animals. Latent trigeminal ganglionic infection was established in Balb/c mice and New Zealand rabbits following corneal inoculation with HSV-1 W strain, and later confirmed by co-cultivation. Treatment with coded eye drops (thymoxamine, corynanthine or BSS was begun one day prior to iontophoresis induction and continued BID OU for 5 days. Reactivation and recovery of latent HSV-1 was determined by daily ocular swabs, and characteristic HSV-1 cytopathic effect in Vero cells. In Balb/c mice, topical administration of thymoxamine 0.5% or corynanthine 5% significantly reduced the number of virus-positive eyes, virus-positive mice, and total virus-positive swabs per experiment, whereas the inhibitory effect was minimal in NZ rabbits. We conclude that alpha blockade may alter the reactivation signal that is mediated via the adrenergic system, and that different host factors (as expressed in different species) may play an important role in this process.

Effect of immunization and immunosuppression on induced ocular shedding and recovery of herpes simplex virus in infected rabbits

Immunization and immunosuppression were evaluated during latent ocular herpes simplex virus, type 1 (HSV-1) infection in the rabbit, using the following parameters: (1) ability to recover virus from preocular tearfilm cultures; (2) reactivation of latent infection by direct electrical stimulation; and (3) recovery of virus from latently infected ganglia by whole-cell co-cultivation. Immunization prior to ocular inoculation of virus significantly reduced both the titer of virus shed into the tearfilm and the duration of virus shedding during primary ocular infection. Half of the non-immunized control rabbits died secondary to virus encephalitis, whereas none of the immunized rabbits died. The immunized rabbits could not be induced to shed virus by electrically stimulating the trigeminal ganglion directly. Immunosuppression of latently infected rabbits with high-dose cyclophosphamide (300 mg kg-1) enhanced virus shedding in the tearfilm and increased mortality due to viral encephalitis. Low-dose cyclophosphamide immunosuppression (40 mg kg-1) did not increase mortality because of viral encephalitis. Tearfilm virus shedding secondary to electrical induction in high-dose and low-dose cyclophosphamide animals was higher than that of control, non-immunosuppressed animals.

Inflammatory sensory polyradiculopathy and reactivated peripheral nervous system infection in a genital herpes model

To study effects of herpesvirus reactivation on the nervous system, mice with latent genital herpes simplex virus type 2 (HSV-2) infections were immunosuppressed. Reactivated infection was detected by virus isolation or by antigen screening in histological sections of spines that contained cords, roots, and dorsal root ganglia. In ganglia, viral antigen was restricted to 2 distinct groups at T9-L2, and L6-S2 levels. In some ganglia, antigen was found in up to 4% of non-contiguous neurons, in their axons, and in endoneurial and satellite cells. Nerve roots distal to ganglia contained a few antigen-positive endoneurial cells and axons, but convincing antigen was not seen in proximal roots. Rare foci of anterior horn cells in the lower cord were the only central sites found to contain antigen. Comparison of antigen-containing ganglionic neuron counts to vaginal culture data indicate that peripheral virus shedding may depend on the number of neurons with reactivated infection. In non-immunosuppressed, latently infected mice, virus recovery was restricted to ganglionic explants from lower thoracic and lumbosacral regions; these ganglia contained no infectious virus in homogenates and no detectable antigen. These mice had an inflammatory polyradiculopathy in a similar distribution to virus found in latent and reactivated infection. The data show that genital HSV-2 infection can result in more extensive ganglionic latency and peripheral nervous system disease than has previously been recognized. Immunosuppression leads to reactivation and widespread, anatomically restricted antigen expression in many ganglia, consistent with the innervation of the genitourinary tract. Decalcified spine preparations provide a sensitive and simple way to detect virus reactivations and disease in these neural tissues.

Studies of herpes virus latency in the sensory spinal ganglia of rabbits

Experimental latent herpes infection of rabbit dorsal root ganglia (DRG) is reported. The simian herpes virus used was derived from fatal natural infection in owl monkeys and has limited neurotropism in the rabbit. Following intradermal injection of the flank it causes a local lesion followed only by dorsal root ganglionitis; segmental paraesthesia and/or sensory loss going on to clinical recovery. Methods were developed for mapping sensory losses. Virus could be immediately re-isolated from skin or DRG homogenates in the acute (first week) stage but from 8-550 days by DRG organ culture only. Spontaneous recurrence does not occur but reactivation can be provoked. The system provides an improved analogue model for the study of the pathogenesis and symptomatic treatment of herpes zoster.

In vivo reactivation of herpes simplex virus in rabbit trigeminal ganglia: electrode model

The rabbit provides an excellent model for the study of ocular herpes because herpetic keratitis in the rabbit eye resembles human disease in its clinical features and in its propensity for spontaneous recurrence. This paper presents a method for the electrical induction of multiple episodes of in vivo reactivation of latent HSV-1 infection with peripheral shedding of virus. Physiological levels of current delivered via an electrode implanted over the trigeminal ganglion of latently infected animals has enabled us to modify and synchronize virus shedding in preocular tear film and to cause multiple episodes of reactivation in a single animal. For this reason, the model is well suited for antiviral efficacy testing and provides an excellent opportunity for investigation of virus-host cell interactions in latent and recurring herpetic disease.

Effect of immunosuppression on recurrent herpes simplex in mice

Mice latently infected with herpes simplex virus were treated with immunosuppressive drugs either alone or combined with stimuli to the skin. Treatment with cyclophosphamide reduced spleen weights and severely depressed lymphocyte levels, but had no effect on healing after cellophane tape stripping (CTS) and did not affect the cutaneous hypersensitivity response after injection of inactivated herpes simplex virus. The drug, either used alone or combined with CTS, failed to increase the incidence of recurrent clinical disease, but increased the incidence of virus isolation after CTS. Prednisolone and azathioprine used together also reduced spleen weights and circulating lymphocyte levels. They slightly delayed healing after CTS, but had no effect on cutaneous hypersensitivity to herpes simplex virus. The treatment, either used alone or combined with CTS, slightly increased the incidence of recurrent clinical disease but did not increase the incidence of virus isolation after CTS. Treatment with antithymocyte serum severely depressed the levels of circulating lymphocytes and delayed the regression of HeLa cell tumors in mice. Used alone, the treatment slightly increased the incidence of recurrent clinical disease, but it failed to increase the incidence of recurrences after CTS. It increased the duration of recurrent herpetic lesions, although in uninfected mice healing after CTS was not affected. Silica altered the clinical course of primary infection with herpes simplex virus and increased the incidence of latency in the ganglia. It also delayed healing after CTS in uninfected mice, so it was not tested when recurrent herpes after CTS was assessed clinically. Treatment with silica alone did not increase the incidence of recurrent clinical disease or the incidence of virus isolation after CTS. The results demonstrate that potent immunosuppressive drugs are much less effective than simple cutaneous manipulation in inducing recurrent lesions, and thus argue strongly for the importance of local factors in the pathogenesis of disease.

Activation of latent herpesvirus hominis in explants of rabbit trigeminal ganglia: the influence of immune serum

More than fifty albino rabbits were inoculated into the right scarified cornea with 10(7) PFU of the Kupka strain of human herpes virus type 1 (HHV-1). At intervals ranging from 4--280 days post infection (p.i.), both gasserian ganglia, both trigeminal nerve trunks and pieces from brain stem and from both corneas were explanted. Activation of the latent HHV-1 was found mainly in the homolateral ganglion tissue, but also in explants originating from the opposite ganglia. Within 24--72 hours, prior to the release of virus into the medium, one infectious unit of HHV was recovered from 10(4)--10(5) cells of the ganglion explant. In addition, a few neurons and satellite cells revealed the presence of virus-specific antigens when the explants were examined by immunofluorescence in serial sections. If the gangia were explanted in the presence of immune serum, the virus recovery rate was at least twice lower as compared to the virus activation in explants kept in the absence of immune serum.