In this 2-part review, I will focus on emerging
virus infections of the central nervous system (CNS). Part 1 will introduce the basic features of emerging
infections, including their definition, epidemiology, and the frequency of CNS involvement. Important mechanisms of emergence will be reviewed, including viruses spreading into new host ranges as exemplified by West Nile virus (WNV),
Japanese encephalitis (JE) virus, Toscana virus, and enterovirus 71 (EV71). Emerging
infections also result from opportunistic spread of viruses into known niches, often resulting from attenuated host resistance to
infection. This process is exemplified by transplant-associated cases of
viral CNS infection caused by WNV, rabies virus,
lymphocytic choriomeningitis, and
lymphocytic choriomeningitis-like viruses and by the syndrome of human herpesvirus 6 (HHV6)-associated posttransplantation acute
limbic encephalitis. The second part of this review begins with a discussion of JC virus and the occurrence of
progressive multifocal leukoencephalopathy in association with novel
immunomodulatory therapies and then continues with an overview of the risk of
infection introduced by imported animals (eg, monkeypox virus) and examples of emerging diseases caused by enhanced competence of viruses for vectors and the spread of vectors (eg, chikungunya virus) and then concludes with examples of novel viruses causing
CNS infection as exemplified by Nipah and Hendra viruses and bat lyssaviruses.