The evolving epidemiology of viral encephalitis.

PURPOSE OF REVIEW: The introduction of West Nile virus to North America illustrates the potential emergence of novel encephalitic agents in unexpected settings. There has been continued recognition of emerging neurotropic viruses in both the developed and developing world and novel modes of transmission of these agents. This review describes recent developments in the epidemiology of West Nile virus and several other emerging viral encephalitides in the developed and developing world and the emergence of novel mechanisms of transmitting viral encephalitis.

RECENT FINDINGS: West Nile virus has continued to have a large public health impact in North America. Improvements in blood donor screening have decreased transfusion-associated transmission of the virus. Monkeypox, with associated encephalitis, occurred in the US. Chandipura virus, an infrequently recognized rhabdovirus, was attributed to large outbreaks of viral encephalitis; however, compelling evidence suggests that the relationship of illness and the virus are questionable. Recent cases of transfusion-associated and transplant-associated viral encephalitis, including West Nile virus, rabies virus, and lymphocytic choriomeningitis virus, were described.

SUMMARY: Continued West Nile virus activity in North America reinforces the fact that viruses can emerge and thrive in new environments and unexpected settings and suggests the need for continued surveillance. Transfusion-associated and transplant-associated viral encephalitis may be an underrecognized risk of these procedures.