Herpes simplex virus encephalitis (HSVE) is an encephalitis with a predelection for the temporal lobes and related structures that is caused by HSV-1 or HSV-2. Because HSV has many properties that would be ideal for a gene transfer vector targeting the nervous system, an understanding of HSVE is of experimental, as well as clinical, .importance to neuroscientists. Herpesviruses have a characteristic architecture of the virion. The molecular aspects of HSVE include the consequences of latency and neurovirulence. Studies on neurovirulence have focused on peripheral multiplication of HSV, the invasion of the CNS, and growth in the CNS. The virus appears to gain access to the CNS via the olfactory and trigeminal nerves and, transneuronally, the limbic system. The definition of latency has still to be clarified; in general, latency includes three separable phases: establishment, maintenance, and reactivation. In humans, there exists a large overlap of clinical presentations of patients with HSVE and those of patients with encephalitis of other origin. However, the presence of memory loss, personality changes, and olfactory hallucinations correlate with the limbic and temporal lobe pathology in HSVE and are characteristic. Several factors correlate with poor outcome in patients: age, time of establishment of therapy, and level of consciousness on admission of patients. The Neuroscientist 2:44-54, 1996
KC/ WORDS Herpes simplex virus infections, CNS, Clinical, Evperimenta!Epidemiology of HSVE HSVE is a unique focal encephalitis, with a predilection for olfactory and limbic parts of the brain, that has an incidence of 1/250,000 to 1/300,000. This review concentrates on various aspects of HSV and HSVE, because this disorder is of interest both to clinical and basic neuroscientists and also because HSV's unique properties make it an excellent candidate as a gene transfer vector that targets particular parts of the brain. HSVE occurs throughout the year, one-third occurring in patients less than 20 years of age; one-half of the patients are more than 50 years of age. Mortality without treatment is 70%. Medical costs for hospitalization of HSVE patients alone are considerable, being over $25 million in the United States in 1983 (1). In adults and older children, HSVE is usually caused by HSV-1, whereas HSV-2 causes a benign lymphocytic meningitis. However, 6 of 93 consecutive Swedish cases of HSVE have been found to be caused by HSV-2 (2, 3). In newborns, HSV-2 causes ; I diffuse encephalitis, with or without systemic infection by HSV-2. Onethird of all cases of HSVE occur as primary infections in patients without a prior exposure to HSV. The majority of HSVE occurs in patients with preexisting antibodies, although only 10% of these have clinically Address reprint requests to: Ufa Meyding-Lamade. M.D.. Department of Neurology, University of Heidelberg. INF 400, 69120 Heidelberg, Germany.evident recurrent HSV infections, such as herpes labialis. Patients with primary infections are usually less than 18 years of age. HSVE does ...