Chronic Infections by Herpes Simplex Viruses and by the Horse and Cat Herpesviruses

Distribution of herpes simplex virus DNA in the brains of human long-term survivors of encephalitis

We have examined the distribution of type 1 herpes simplex virus (HSV-1) DNA in the brains of 8 humans surviving for between 4 months and 17 years after acute encephalitis. Histological examination showed neuronal loss and gliosis largely confined to the temporal and frontal lobes, typical of HSV-1 encephalitis. There was a widespread persistent inflammatory infiltrate, present in both the cerebrum and brainstem. Viral DNA was detected in paraffin sections of formalin-fixed paraffin-embedded autopsy brain by use of the polymerase chain reaction to amplify a fragment of the HSV-1 thymidine kinase gene. HSV-1 DNA was amplified from the cerebrum in 6/8 cases and from the brainstem in 4/8 cases. These findings suggest the possibility that HSV-1 may persist within the human central nervous system after acute herpes simplex encephalitis. The distribution of the viral DNA correlates better with that of the persistent inflammatory infiltrate than with the destructive lesions of the acute encephalitis.

Regulation of viral and cellular genes in a human neuroblastoma cell line latently infected with herpes simplex virus type 2

A latent state of the herpes simplex virus type 2 genome was established in a human neuroblastoma cell line (SMS-KCNR) to initiate studies on the mechanism by which host cells interact and regulate latent viral genes. To establish viral latency, it was necessary to prevent virus replication by briefly exposing the infected cells to antiherpetic acycloguanosine (20 microM) and human interferon (120 U/ml). Subsequently however, these cells could be propagated without any antiherpetic agents and almost 60% of the cell population contained viral genome. While these cells did not produce any infectious virus, immunoblot analysis revealed two intracellular polypeptides with molecular weights of 87.5 kDa and 67 kDa, respectively, that interacted with hyperimmune anti-HSV2 rabbit serum. Two cellular enzymes, acetylcholinesterase and choline acetyltransferase, involved in metabolism of neurotransmitters were expressed at a higher level in the latently infected cells than in the mock-infected control cells. Infectious HSV-2 could be reactivated from these cells only after the cells had undergone massive morphological differentiation and maturation to flat cell types by extensive treatment with 20 micron bromodeoxyuridine.

Latent herpes simplex virus type 1 transcripts in peripheral and central nervous system tissues of mice map to similar regions of the viral genome

Herpes simplex virus type 1 (HSV-1) DNA and RNA have been detected in peripheral nervous system (PNS) and central nervous system (CNS) tissues of latently infected mice. However, explant methods are successful in reactivating HSV-1 only from latently infected PNS tissues. In this report, latent herpesvirus infections in mouse PNS and CNS tissues were compared by in situ hybridization to determine whether the difference in reactivation was at the level of the virus or the host tissue. It was demonstrated that the HSV-1 transcripts present during latency in the mouse PNS and CNS originated from the same region of the genome, the repeats which bracket the long unique sequence. Therefore, the difference in reactivation with PNS and CNS tissues cannot be accounted for by differences in the extent of the HSV-1 genome transcribed during herpesvirus latency. Latent HSV-1 RNA was detected in the trigeminal ganglia (PNS) and the trigeminal system in the CNS from the mesencephalon to the spinal cord as well as other regions of the CNS not noted previously. Latent HSV-1 RNA was found predominantly in neurons but also in a small number of cells which could not be identified as neuronal cells. It is suggested that host differences in CNS and PNS tissues, rather than differences in latent virus transcription, may be important determinants in the HSV-1 reactivation process in explanted tissues.

Persistent viral infection. The carrier state

A persistent viral infection is one in which the virus in a replicating or non-replicating form persists in the host beyond the normal recovery and elimination period for that particular viral infection. The clinical significance and mechanisms of persistence, when known, are discussed for the important viral infections of dogs and cats. Particular emphasis is given to feline viral rhinotracheitis, feline calicivirus, canine distemper, and feline leukemia.

Infection of specific-pathogen free lambs with a herpesvirus isolated from pulmonary adenomatosis

In two experiments, 18 specific-pathogen free (SPF) lambs were inoculated by several routes with the Scottish strain of caprine herpesvirus 1 (CHV 1). Seventeen of the lambs developed interstitial changes in the lungs ranging from focal cellular infiltration to a widespread proliferative pneumonia. Five weeks after the initial inoculation 3 lambs were given a course of corticosteroid by intravenous injection. Subsequently virus was reisolated from all 3 lambs. Virus was also recovered from one of these lambs on one occasion prior to steroid treatment. It has therefore been established that CHV 1 can cause pneumonia and can be reisolated from infected sheep for at least 6 weeks after infection. It is suggested that CHV 1 might cause a latent infection in sheep which is reactivated following the development of pulmonary adenomatosis.

Encephalitis resulting from reactivation of latent herpes simplex virus in mice

Herpes simplex virus (HSV) encephalitis was produced in mice from reactivation of latent virus. Two experimental models were used: the trigeminal model after corneal inoculation of HSV, and the hypoglossal model after tongue inoculation of HSV. In the trigeminal model, cyclophosphamide treatment induced reactivation of latent virus in ganglia but not in central nervous system tissue. Spread of the reactivated virus from ganglia to brain occurred only in mice deficient in anti-HSV antibody. In the hypoglossal model, sectioning of the hypoglossal nerve provoked chromatolysis in the corresponding central nervous system motor neurons and occasionally reactivated latent HSV in the brains of mice. These results suggest that HSV encephalitis can result from the spread of reactivated virus from ganglia to brain and also from in situ reactivation in brain.

Bovid herpesvirus 2 latency: failure to recover virus from central sensory nerve ganglia

Latent bovid herpesvirus 2 was sought in sensory ganglia, epithelium and lymph nodes from cattle having antibodies against bovid herpes virus 2. Tissues from eight animals were maintained in vitro as explants for 49-72 days during which all expended media was tested for virus. Three animals were pretreated with corticosteroids prior to slaughter. Infectious bovine rhinotracheitis virus was recovered from one animal, but bovid herpesvirus 2 was not detected.

Feline respiratory virus carriers in clinically healthy cats

In two surveys, feline calicivirus was cultured from 19.7% and 15% of 66 and 201 clinically healthy cats respectively. Feline viral rhinotracheitis virus was cultured also from 1.5% of oropharyngeal swabs collected in both surveys. Feline syncytial virus was isolated from 5.5% oropharyngeal swabs collected in the second survey. The use of serological examination and corticosteroid treatment to stimulate virus shedding demonstrated that 25.8% cats in the first survey were carriers of feline viral rhinotracheitis virus. In the second survey, mercapto-ethanol treatment of serum was used to differentiate recent from previous infection with feline viral rhinotracheitis virus and some 18.5% cats had FVR antibody that was resistant to treatment with mercapto-ethanol.

Persistence in herpes simplex virus infections

Diseases of man caused by the virus of herpes simplex fall into two broad categories. The primary disease occurs only once in any individual's life and is caused by transmission of virus from an already infected human. Thereafter, the individual may be subject to recurrent herpetic disease, the manifestations of which are different from the primary disease. Recurrent disease varies in severity from trivial, to incapacitating and frankly lethal (as in diseases resulting from the virus's neurotropic and oncogenic properties). The source of the virus in recurrent herpetic disease has never been conclusively resolved, but is almost certainly endogenous to the patient. Theories, case reports and experiments exist to show that endogenous virus may, in periods of clinical quiescence, be latent (or persistent) at the site of the recurrent lesions itself, or more remotely in nerve tissues related to the site of recurrence.

Depressed specific cell-mediated immunity to Herpes simplex virus type 1 in patients with recurrent herpes labialis

Cell-mediated immunity to herpes simplex virus type 1 (HSV-1) was assessed by a lymphocytotoxicity 51-Cr-release microassay procedure, using the MA-160 human prostatic adenoma cell line chronically infected with HSV-1 and its parent cell line as control. The specific immune release mean plus or minus standard deviation for nine asymptomatic patients with recurrent HSV-1 infections was 13.7 plus or minus 8.1%, compared to 28.9 plus or minus 8.4% in seven normal seropositive controls (P is less than 0.01). In four additional patients studied serially, the cell-mediated immunity was significantly increased during the recrudescence of herpetic infection, with a mean specific immune release value of 51.7 plus or minus 27.8%, compared to 8.7 plus or minus 1.5% during the convalescent period 2 to 10 weeks later (P is less than 0.05). These findings suggest that patients with recurrent HSV-1 infections have vigorous cellular immune responses during the acute phase but a specific impairment of cell-mediated immunity during the quiescent period, which may in part account for their susceptibility to recurrent herpetic infections.

Herpes genitalis in guinea-pigs. I. Kinetic study in infection with Herpesvirus hominis type 2

The kinetics of virus replication after vaginal infection of guinea-pigs with HVH 2/Angelotti were studied in relation to the appearance of local and general symptoms. Most virus was isolated from the genital tract 24-48 hours post infection. Virus was first isolated from the spinal cord 48-72 hours post infection. Penetration into the brain only occurred occasionally, and later. Under the experimental conditions employed, no virus was found in the blood, spleen, kidneys, adrenals or inguinal lymph nodes. The local symptoms (typical genital herpes) and the general symptoms (paralysis and death) started after maximum virus replication had been reached and seemed to be a consequence of neural, rather than of haematogenic or lymphogenic spread.

Exacerbation and reactivation of Herpesvirus hominis infection in mice by cyclophosphamide

Cyclophosphamide has been shown to potentiate the growth of Herpesvirus hominis in the skin of Webster Schneider mice. Higher skin yields of virus were obtained, marked dissemination of virus to the brain was produced and mortality in mice was increased. Serum neutralizing antibody titres were suppressed. The system may serve as a good model for the study of specific antiherpes drugs.

Chronic infection of the rabbit central nervous system by a slowly growing equine herpesvirus

The spinal cords of rabbits were chronically infected by a slowly growing horse herpesvirus (a "cytomegalovirus") inoculated directly therein. Virus was recovered from the central nervous systems of some of such animals after more than 1 year. The virus could be reisolated from all the animals killed during the first few weeks after its injection; acute focal meningomyelitis was present with involvement of gray and white matter of the cervical, thoracic, and lumbar levels of the spinal cords of these rabbits, though the nerve cells themselves remained undamaged. Thereafter, reisolation of the virus became sporadic, and no damage to the spinal cord could be histologically discerned even in animals from which the virus was recovered. No paralytic or other clinical effects could be attributed to the infection.