Changing epidemiology of viral encephalitis in the Old World
Abstract number: S284
Avsic Zupanc T.
Encephalitis can be caused by wide variety of infectious agents, including viruses, bacteria, fungi and parasites. In addition to common viral pathogens, arthropod-borne viruses (transmitted through insect or tick-bite) can cause arboviral encephalitis. In Europe, the most important pathogens responsible for arboviral encephalitis are tick-borne encephalitis virus (TBEV), West Nile virus (WNV) and Sandfly fever virus (SFV). Tick-borne encephalitis (TBE) is the most important flavivirus infection of the central nervous system (CNS) in Europe and Russia. The epidemiology of TBE is closely related to the ecology and biology of ticks. In nature, TBE virus is propagated in a cycle involving permanently infected ticks and wild vertebrate hosts. Virus transmission occurs horizontally between tick vectors and vertebrates, with small mammals serving as virus reservoirs. TBE is distributed in an endemic pattern of natural foci over a wide geographical area focused on central Europe, the Baltic States and Russia. During the past two decades, both new endemic foci and an increase in cases have been reported in many European countries, with the major exception being Austria, which has a high vaccine coverage (>86%). The disease has also been considered outside the traditional endemic areas. Some reports of new endemic areas are attributed to a previous under diagnosis of cases. However, the true nature of this rise is supported by an increase in areas with high awareness of the disease and with well established diagnostic routines. Environmental factors important for sustaining natural foci for tick-borne encephalitis can be modeled with satellite data. These models suggest that climate change is partly responsible for increased incidence in Europe. But, existing methods for risk assessment have limitations. Thus, risk assessment should combine human habits and socioeconomic variables with functional variables in natural foci. West Nile virus (WNV) is a flavivirus that is maintained in a bird-mosquito transmission cycle. Humans and horses are usually incidental hosts. Historically, WNV has been associated with asymptomatic infections and sporadic disease outbreaks in humans and horses in Africa, Europe, and Asia. Although, WN fever was a minor arbovirosis, some cases of encephalitis associated with fatalities were reported in Israel in the 1950 s. However, after few silent decades, the virus has caused frequent outbreaks of severe neuroinvasive disease in humans and horses in Europe and the Mediterranean Basin. Even more, new modes of transmission through blood donations, organ transplants, and the intrauterine route have been reported. In Europe, an enhanced surveillance of WN infection in humans, horses, birds, and vectors may reveal the presence of the virus in different locations. Nevertheless, outbreaks of WN virus remain unpredictable. Further coordinated studies are needed for a better understanding of the ecology and the pathogenicity of the WN virus.
|Session name:||19th European Congress of Clinical Microbiology and Infectious Diseases|
|Location:||Helsinki, Finland, 16 - 19 May 2009|
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