VIRAL ENCEPHALITIS (FLAVIVIRUSES)
The viral genus Flavivirus is a very serious public health threat. Twentytwo of the 34 mosquito-borne flaviviruses cause human disease.2 In some strains, the flavivirus enters the brain’s blood vessels and nerves and causes brain inflammation, which is known as encephalitis.3 In the most severe cases, this inflammation may cause debilitating irreversible nerve damage, brain tumors, and death.4 The lethality of encephalitis can be as high as 37%, although it varies by strain.3
There are some prophylactic measures against viral encephalitis and one synthetically created acyclic nucleoside analog, Acyclovir,1–3 and many companies are working to develop a vaccine. However, since such a vaccine does not currently exist for the most common strains of encephalitis in the United States, it is a major bioterrorist threat. Its danger is increased by the ease of transmission from mosquitoes (mainly the culex species) and ticks and by their many breeding grounds.1,5 However, because of its moderate to low mortality rate, its moderate ease of dissemination, and the fact that it requires specific enhancements of the Centers for Disease Control and Prevention’s (CDC) diagnostic capacity and enhanced disease surveillance, the CDC categorizes viral encephalitis as a Category B bioweapon threat and a Biosafety Level 3 pathogen.3
Encephalitis is derived from the Greek word encephalo (“brain”) and the Greek word itis, a term used pathologically to indicate inflammation of an organ or an abnormal state or condition. Thus, taken together, encephalitis literally means “inflammation of the brain,” which is precisely what advanced encephalitis is and what causes its potential lethality. However, unlike meningitis, which is limited to inflammation of the meninges of the brain, encephalitis involves inflammation of both the meninges and the parenchyma1,7’12’18 (figure 2.1A and B).