**3. Measles Inclusion Body Encephalitis (MIBE)**

160 Non-Flavivirus Encephalitis

Table 1. Encephalitis Caused by Measles Virus

The disease occurs at any age in immunocompromised patients after MV exposition. MIBE affects persons with congenital or adquired cell-mediated immunodeficiency as oncologic (approximately 70% of MIBE cases occurring in acute lymphocytic leukaemia), transplanted or HIV-infected patients. In severily inmmunodeficient patients the live attenuated measles vaccine in use may also cause MIBE. It has been described one fatal case of MIBE in a boy with chronic granulomatous disease after stem cell transplant without a history of recent clinical measles in the donor or the receptor (Bitnum et al.1999).

Typically, the onset occurs within one year of MV infection. MIBE may accompany or follows measles giant cell pneumonia, but more often occurs as the sole clinical manifestation, two to six months after MV infection or vaccination. Patients usually present with afebrile refractory focal seizures and altered mentation, and progress to generalized seizures, coma and death. CSF parameters are often normal and unlike SSPE hyperimmune antibody response to MV and oligoclonal bands may be not detected. EEG are abnormal, but unspecific; head computed tomography (CT) and Nuclear Magnetic Images (MRI) scans are normal. The mortality exceeds 85%, and survivors have severe neurological sequelae. At autopsia or biopsia the brain show gliosis and focal necropsia, lymphocyte perivascular cuffing, and intranuclear and intracytoplasmic inclusions in glial cells and neurons. MV nucleocapsids can be detected by electron microscopy, MV antigens by immuno-assays, and MV RNA by in situ hybridization or RT-PCR.

The virus persists and progressively invades the brain over months. At a brain autopsia from a patient with MIBE, R. Cattaneo, M. Billeter and collaborators first reported the phenomena of biased U to C RNA hypermutation in the MeV genome (Cattaneo et al, 1988). This hypermutation may take place by the enzyme Adenosine deaminasa ADAR present in nervous tissue which would transform Adenosine into Inosine in the replicative intermediary RNA (see below).
