Demonstration of vaccinia virus antigen in brains of postvaccinal encephalitis cases

The role of non-human primates in the neurological safety of live viral vaccines (review)

This review covers comprehensive data accumulated during the long history of using monkeys in the determination of neurovirulence activity and safety of live poliomyelitis, flaviviral, smallpox and mumps vaccines, as well as newly developed transgenic mouse and molecular-biological tests. The review also analyzes processes caused by some of these viruses in infant rodents (mice, rats) and evaluates the role of these processes in vaccine safety control. Recommendations resulting from this analysis are presented.

Comparison of methods for detection of vaccinia virus in patient specimens

We analyzed a shell vial culture assay (SVA), real-time PCR, and a direct fluorescent antibody assay (DFA) for rapid detection of vaccinia virus from vaccination sites of Dryvax vaccine recipients. Of 47 samples assayed, 100% were positive by PCR, 89% were positive by SVA, and 40% were positive by DFA. DFA was limited by the need for adequate numbers of cells, with 32% of samples inadequate for interpretation. DFA performed better with specimens from patients who had not previously received the vaccine. PCR was positive for longer times postvaccination than was SVA. Infectious virus could be recovered after 45 min of acetone fixation of shell vial coverslips. Commercially available polyclonal antibodies cross-reacted with other orthopoxviruses and herpes simplex 1, but commercially available monoclonal antibodies were specific for vaccinia virus. In summary, PCR was the most sensitive test for detecting vaccinia virus in clinical specimens, while the DFA was the most rapid but the least sensitive test.

Disseminated hemorrhagic leukoencephalomyelitis with localized herpes simplex brain stem infection

A case of widespread hemorrhagic and perivenous demyelinative leukoencephalomyelitis complicating a localized herpes simplex virus (HSV) brain stem infection is reported in a 28-year-old man. The presence of the virus is documented immunohistochemically and ultrastructurally. The spinal trigeminal tract at the level of the medulla oblongata contained viral antigen in the neurons, glia and in the vascular walls, including a few endothelial cells. The foci of demyelination showed deposits of gamma globulins and slight inflammatory infiltrations; the virus was absent from these lesions. It is postulated that HSV entered the central nervous system through the trigeminal nerve. Focal expression of the viral antigen on the endothelium in a sensitized host was the likely precipitating factor in the hyperacute autoimmune reaction, resulting in the widespread hemorrhagic and demyelinating lesions in the central nervous system.

Poxvirus deletion mutants: virulence and immunogenicity

Post-vaccinial encephalitis and disseminated vaccinia are major concerns with the use of vaccinia virus recombinants as immunization vectors in man. To identify and characterize possible attenuated poxvirus vectors, rabbitpox virus (RPV) (closely related to vaccinia) and four deletion mutants of RPV were studied for organ tropism, neurovirulence, and protection from wild-type challenge in BALB/c mice. Intraperitoneal (IP) inoculation with 10(7) PFU wild-type (wt) RPV or with two mutants 8 sm and 28 (containing approximately 12 kilobase deletions) showed titers of greater than 10(3) PFU/g tissue in multiple organs. In contrast, IP inoculation of 10(7) PFU of mutants 31 or 23 (containing approximately 30 kilobase deletions) showed markedly reduced growth in all organs. Neurovirulence of wt and mutant RPV was determined by intracerebral (IC) inoculation of mice. Wt and mutants 8 sm, and 28 RPV had LD50 less than 10(2) PFU; in contrast, 31 and 23 had LD50 greater than 10(5) PFU. Finally, 10(6) PFU of mutants 31 or 23, were administered to mice by scarification, the normal route of vaccinia immunization. Both 31 and 23 grew locally in the skin and protected mice challenged IC at 21 days with 100 LD50 of wt RPV, while all unimmunized controls died. We conclude that deletion mutants 31 and 23 demonstrate markedly reduced invasiveness and neurovirulence while retaining immunogenicity. Similar deletion mutations in vaccinia may create avirulent, but effective vaccine vectors for man.

Disseminated vasculomyelinopathy in the peripheral nervous system mediated by immune complexes (ICs). Immunohistochemical studies of sciatic nerves in chronic serum sickness (CHSS) in rabbits

Histological examination of 20 sciatic nerves from rabbits with experimental chronic serum sickness (CHSS) revealed patchy vasculitis of the vasa nervorum of various intensity. The vessel lesions ranged from endothelial proliferation to vessel wall necrosis with fibrinoid degeneration and infiltration by lymphocytes, plasma cells, macrophages and, sporadically, by neutrophils. Perivascularly, there were oedema, chronic infiltrates or small haemorrhages. The myelinated fibres in close relation to the vascular system were focally depleted and features of perivascular demyelination were found. Teased fibres showed paranodal and segmental demyelination, axonal degeneration and, sporadically, remyelination. In all cases, immunofluorescent deposits of bovine serum albumin (BSA), IgG and C3 complement were found in and around some vasa nervorum. Other indirect evidence for immune complex (IC) deposition was provided by ultrastructural examination where vascular and endoneurial osmophilic deposits were found; in 4 cases with paracrystalline organization resembling cryoglobulin component. IC-mediated vasculitis led to blood-nerve barrier impairment and leakage of serum proteins into the endoneurial space. The morphological and immunohistochemical changes in this model which develop after a latency period of 2 or more weeks, strongly resemble those observed in human acquired inflammatory demyelinating polyradiculoneuropathies or in connective tissue diseases.

Metabolic studies on vaccinia-virus-infected oligodendrocytes in brain cell cultures

Twelve-day-old cultures of dissociated newborn mouse brain were infected with neurotropic vaccinia virus strain WR. Using the indirect immuno-fluorescence staining technique the total destruction of galactocerebroside (GL) or myelin basic protein (MBP)-positive oligodendrocytes could be detected after 72 h of infection. The activity of the oligodendrocyte-specific enzymes, cerebroside sulfotransferase (CST) and 2'3'-cyclic nucleotide 3'-phosphohydrolase (CNP), was 27% and 17% respectively of the activity in noninfected controls. This reduction was not a result of viral-induced inhibition of host protein synthesis. In cultures treated with puromycin GC- and MBP- positive oligodendrocytes were detectable at a time at which no CST or CNP activity could detected.

Pathogenicity of a vaccine strain of vaccina virus in rabbits administered by intravenous route

The pathogenicity of the Lister (Elstree) strain, a vaccinia virus, in rabbits after intravenous injection was studied by histopathological and immunofluorescent methods. Inoculation of 1 X 10(7) PFU (pock-forming unit) virus into weanling and young adult rabbits caused severe emaciation and high mortality within 2 weeks. Pathological findings were characterized by vesicular lesions along muco-cutaneous junction areas of the eyes, nose and mouth and by inflammatory changes in the brain, mainly in the meninges and choroid plexus. Immunofluorescent staining of the tissues of animals sacrificed at intervals demonstrated the accumulation of vaccinia viral antigen (s) in the loci of pathological changes. The suitability of this model system for the study of pathogenesis of human postvaccinal meningoencephalitis is discussed.