S-106. Overview of viral encephalitis

Fever and altered sensorium constitute the encephalitis syndrome which can be due to a number of infectious (meningitis, malaria, neurocysticercosis and septic encephalopathy) or non infectious (electrolyte imbalance, mitochondrial cytopathy, collagen vascular disease and rare metabolism disorders e.g. glutaric aciduria type 1, biotinidase deficiency). Amongst the viral encephalitis, it is critical to define encephalitis e.g. herpes simplex, Epstein Barr, cytomegalo and herpes zoster encephalitis which can be treated by special antiviral drugs. Amongst the other endemic encephalitis Japanese encephalitis is the most important in South East Asia and occurs during post monsoon period. It is characterized by encephalomyelitis syndrome associated with various movement disorders, anterior horn cell involvement and typical radiological changes (thalamic, basal ganglia and brainstem). Dengue virus has also been reported to result in encephalopathy/encephalitis which can be clinically suspected by presence of thrombocytopenia, hepatosplenomegaly, liver and renal dysfunction and flaccid quariplegia due to myositis. These encephalitis has been reported from Northern, Eastern and also in South India. Chickenguinea is reported from South and West India and results in diverse neurological manifestations. Mumps, measles and enterovirus encephalitis also have been reported from time to time. West Nile encephalitis has been reported from West India which results in encephalomyelitis syndrome and MRI findings similar to JE but comprehensive reports are lacking from India. Emerging viral infections like Nipah from Bengal and Chandipura from South India have been a matter of great concern. In spite of best effort more than 30% of viral encephalitides remain undiagnosed and pose challenge to both clinicians and virologists.