Abstract
Arboviruses are transmitted in nature exclusively or to a major extend by arthropods. They belong to the most important viruses invading new areas in the world and their occurrence is strongly influenced by climatic changes due to the life cycle of the transmitting vectors. Several arboviruses have emerged in new regions of the world during the last years, like West Nile virus (WNV) in the Americas, Usutu virus (USUV) in Central Europe, or Rift Valley fever virus (RVFV) in the Arabian Peninsula. In most instances the ways of introduction of arboviruses into new regions are not known. Infections acquired during stays in the tropics and subtropics are diagnosed with increasing frequency in travellers returning from tropical countries, but interestingly no attention is paid on accompanying pet animals or the hematophagous ectoparasites that may still be attached to them. Here we outline the known ecology of the mosquito-borne equine encephalitis viruses (WEEV, EEEV, and VEEV), WNV, USUV, RVFV, and Japanese Encephalitis virus, as well as Tick-Borne Encephalitis virus and its North American counterpart Powassan virus, and will discuss the most likely mode that these viruses could expand their respective geographical range. All these viruses have a different epidemiology as different vector species, reservoir hosts and virus types have adapted to promiscuous and robust or rather very fine-balanced transmission cycles. Consequently, these viruses will behave differently with regard to the requirements needed to establish new endemic foci outside their original geographical ranges. Hence, emphasis is given on animal trade and suitable ecologic conditions, including competent vectors and vertebrate hosts.
Highlights
During the last decades the appearance of new infectious diseases and an increasing invasion of diseases into new areas created a new category of pathogens: emerging and re-emerging pathogens
The analysis showed that the highest risk of an introduction of West Nile virus (WNV) is infected mosquitoes un-intentionally transported in airoplanes carrying tourists
Arboviruses are maintained in nature in complex transmission cycles between arthropods and vertebrates
Summary
During the last decades the appearance of new infectious diseases and an increasing invasion of diseases into new areas created a new category of pathogens: emerging and re-emerging pathogens. WEEV is maintained in North America in a natural transmission cycle involving domestic and wild birds as the most important maintenance and amplifying vertebrate hosts and mosquito vectors, primarily Culex tarsalis [[21], Figure 1]. RVFV may be transmitted to other mosquito species which serve as bridging vectors to other wild and domestic animals and to humans which may cause further amplification of the transmission cycle [[84], Figure 4]. These examples show that RVFV, without any doubt, is one of the most aggressive migrating arbovirus. It was transported to Norway where it is dispersing, possibly due to climatic changes, to the north [125]
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