Viral encephalitis dissemination

Other acquired disorders affecting myelin in humans may be secondary to viral infections, neoplasias or immunosuppressive therapy. Acute disseminated encephalomyelitis, also called postinfectious or postimmunization encephalitis, represents a group of disorders usually of mixed viral-immunological etiology. The condition is most commonly related to a spontaneous viral infection, of which major examples are measles, smallpox or chickenpox [1,2]. 

Vidarabine is used mainly in human HSV-1 and HSV-2 encephalitis, decreasing the mortality rate from 70 to 30%. Whitley et al. (57) reported that early vidarabine therapy is helpful in controlling complications of localized or disseminated herpes zoster in immunocompromised patients. Vidarabine also is useful in neonatal herpes labialis or genitalis, vaccinia virus, adenovirus, RNA viruses, papovavirus, CMV, and smallpox virus infections. Given the efficacy of vidarabine in certain viral infections, the U.S. FDA approved a 3% ointment for the treatment of herpes simplex keratoconjunctivitis and recurrent epithelial keratitis, and a 2% IV injection for the treatment of herpes simplex encephalitis and herpes zoster infections (Table 43.3). A topical ophthalmic preparation of vidarabine is useful in herpes simplex keratitis but shows little promise in herpes simplex labialis or genitalis. The monophosphate esters of vidarabine are more water-soluble and can be used in smaller volumes and even intramuscularly. These esters are under clinical investigation for the treatment of hepatitis B, systemic and cutaneous herpes simplex, and herpes zoster virus infections in immunocompromised patients. 

Harper was one of the first investigators to study viral aerosols and he showed that survival depended very much on the composition of the disseminating fluid. Poliovirus and Foot and Mouth virus survive best at high RH whereas Semliki Forest virus, vaccinia, Venezuelan Equine Encephalitis and influenza virus are most stable at low RH. The DNA-containing viruses, pigeon pox virus, and Simian virus 40 maintain their infectivity over a wide range of RH. 

Herpesvirus 6 (HHV 6) is the etiologic agent for exanthema subitum, a common fever and rash syndrome of childhood. Rarely, HHV-6 causes bone-marrow suppression, pneumonia, or encephalitis. HHV-6 encodes a chemokine homologue named U83, which induces chemotaxis of the monocytic cell line THP-1 (Zou et al, 1999). It is still unclear whether the infected cells secrete this chemokine, but because the virus typically infects monocytes, U83 is hypothesized to be important for viral dissemination. 

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