From the Los Angeles County
Department of Health Services
"Public Health Letter"
December 1994

Atypical Viral Encephalopathy (Stealth Virus)

Atypical cytopathic viruses have been isolated from the blood and cerebrospinal fluid (CSF of patients with otherwise unexplained encephalopathic illnesses; several of these patients have presented with an acute onset of severe cognitive dysfunction, mood and personality changes, headaches, and lethargy. Routine neurological examination and CSF analyses have generally revealed minimal or no abnormalities. While the patients showed some improvement with time, they continued to have cognitive impairment, unexplained fatigue, lowered pain threshold, depression, and other symptoms consistent with a dysfunctional brain syndrome. Molecular studies on some of the viral isolates indicate a relatedness to human herpesviruses with evidence for widespread genetic mutations and gene deletions. These viruses have been termed "stealth viruses" because of the absence of the usual inflammatory response evoked by conventional herpesviruses. A prototype stealth virus was described in a recent publication.1

1Cytomegalovirus-related sequences in an atypical cytopathic virus repeatedly cultured from a patient with chronic fatigue syndrome. American Journal of Pathology 1994; 145:440-451.

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