Fatal herpes simplex encephalitis with demonstration of virus in the olfactory pathway

Changing spectrum of acute encephalitis syndrome in India and a syndromic approach

Acute encephalitis syndrome (AES) refers to an acute onset of fever and clinical neurological manifestation that includes mental confusion, disorientation, delirium, or coma, which may occur because of infectious or non-infectious causes. Cerebrospinal fluid (CSF) pleocytosis generally favors infectious etiology, and a normal CSF favors an encephalopathy or non-infectious AES. Among the infectious AES, viral, bacterial, rickettsial, fungal, and parasitic causes are the commonest. Geographical and seasonal clustering and other epidemiological characteristics are important in clinical decision making. Clinical markers like eschar, skin rash, myalgia, hepatosplenomegaly, thrombocytopenia, liver and kidney dysfunction, elevated serum CK, fronto-temporal or thalamic involvement on MRI, and anterior horn cell involvement are invaluable clues for the etiological diagnosis. Categorizing the AES cases into neurologic [Herpes simplex encephalitis (HSE), Japanese encephalitis (JE), and West Nile encephalitis (WNE)] and systemic (scrub typhus, malaria, dengue, and Chikungunya) helps in rational utilization of diagnostic and management resources. In neurological AES, cranial CT/MRI revealing frontotemporal lesion is consistent with HSE, and thalamic and basal ganglia lesions are consistent with JE. Cerebrospinal fluid nucleic acid detection test or IgM antibody for JE and HSE are confirmatory. Presence of frontotemporal involvement on MRI indicates acyclovir treatment pending virological confirmation. In systemic AES, CT/MRI, PCR for HSE and JE, and acyclovir therapy may not be useful, rather treatable etiologies such as malaria, scrub typhus, and leptospirosis should be looked for. If smear or antigen for malaria is positive, should receive antimalarial, if negative doxycycline and ceftriaxone should be started pending serological confirmation of scrub typhus, leptospira, or dengue. A syndromic approach of AES based on the prevalent infection in a geographical region may be developed, which may be cost-effective.

Experimental equine herpesvirus-1 infection in llamas (Lama glama)

Three llamas (Lama glama) were experimentally infected intranasally with an isolate of equine herpesvirus-1 (EHV-1) from the brain of an alpaca that had experienced severe neurologic signs. Two of the 3 llamas developed severe neurologic disorders following inoculation; 1 died, and 1 was euthanized in a moribund state. The third llama showed only mild neurologic signs. The euthanized llama had preexisting antibodies to EHV-1, and the remaining 2 llamas were seronegative (virus neutralization titer less than 6) at the time of inoculation. One of the seronegative llamas died acutely without production of detectable antibodies, and the other developed antibodies typical of a primary immune response. The EHV-1 virus was recovered only from a sample of the thalamus of the llama that died acutely. Histopathologic lesions were observed in the brain and retina of the dead and euthanized animals. This study verifies the pathogenic potential of EHV-1 for llamas.

Herpes simplex virus antigen detection in human acute encephalitis: an immunohistochemical study using avidin-biotin-peroxidase complex method

Autopsy specimens from six patients with clinically diagnosed herpes simplex virus (HSV) encephalitis were studied. Since immunocytochemistry has been reported to be a more reliable and successful method to identify HSV as the etiologic agent, antitype 1 HSV (HSV1) and antitype 2 HSV (HSV2) and the avidin-biotin-peroxidase complex (ABC) method were applied to brain paraffin sections. Positive immunostaining was observed in front-orbital, mediobasal temporal lobes, cingulate gyrus, and insula. The staining was bilateral but predominant on one side. In neurons, the cytoplasmic staining was prominent in perikarya and processes, less often observed in nuclei, rarely seen in nuclear inclusions. The positive staining was intense in oligodendrocytes and macrophages, in both nuclei and cytoplasm. In two cases astrocytic processes were stained strongly. Perivascular lymphocytes were always negative. Positive reactions were obtained with both anti-HSV1 and anti-HSV2 but weaker with anti-HSV2. This results suggests that, because of its high sensitivity, ABC method permits viral antigen detection not feasible with other methods. However, this method lacks of accuracy for HSV typing mainly because of probable antigens changes resulting from tissue processing.

Herpes simplex virus encephalitis. Diagnostic and treatment considerations

The patient with meningoencephalitis should be evaluated carefully for the presence of focal signs referable to involvement of the frontotemporal regions of the brain. A significant percentage of cases of encephalitis with discrete focal features are caused by infection with herpes simplex virus. If focal signs are not present, the patient should be managed conservatively but examined regularly because focal neurologic dysfunction may present at any time in the course of disease. If there is clinical and electrographic evidence of involvement of the frontotemporal lobes, radiographic imaging is indicated as well as studies of the serum and cerebrospinal fluid for antibodies indicative of a recent infection with herpes simplex virus. Assuming that the radiographic scans identify the characteristic changes of a focal encephalitis and that the antibody responses are indicative of a recent herpes simplex virus infection, brain biopsy should be done in order to confirm the diagnosis. With positive evidence for HSE, treatment with ara-A should be initiated and continued for 10 days. If the biopsy proves negative for virus, ara-A should be discontinued and the patient managed conservatively (Fig. 3). Although the NIAID study of ara-A treatment of HSE is encouraging, the numbers are small and the evidence is, at best, only suggestive. It is reasonable to use this drug until a better one becomes available for the treatment of known HSE, and treatment should be instituted early before cellular injury is extensive. In centers familiar with this problem, biopsy confirmation of the diagnosis is a simple and informative procedure and can be defended. If patients cannot be moved to a center of this type, physicians familiar with the many facets of this problem should be consulted, and a decision regarding biopsy and treatment should be individualized in light of the circumstances. Biopsy should only be undertaken when the procedure can be done with minimal risk to the patient and the assurance that the maximum amount of information can be gained.

Necropsy study of the olfactory portal of entry in herpes simplex encephalitis

Two fatal cases of sporadic herpes simplex virus (HSV) encephalitis were seen and diagnosed at the Sir Charles Gairdner Hospital, Perth, between 1979 and 1981. Necropsy studies were directed to the possible portal of entry of HSV into the central nervous system. Viruses were present in the left olfactory nerve in one patient. No viruses were found in the Gasserian ganglia of either patient. The finding of HSV within an olfactory nerve provides further evidence of an olfactory portal of entry to the central nervous system in sporadic human HSV encephalitis.