[Tick-borne human pathogenic microorganisms found in Europe and those considered nonpathogenic. Part I: Ticks and Viruses].

The importance of tick-borne encephalitis (TBE) and Lyme borreliosis-the main European tick-borne diseases-is steadily growing. This fact is due to many different factors including climate changes. However, across Europe many other human pathogenic viruses, bacteria, and parasites are found in ticks. This article gives an overview of tick-borne human pathogenic viruses present in Europe as well as those considered nonpathogenic. It also deals with the various species of vector-competent ticks. Among these ticks, viruses from 6 families encompassing 8 genera and 35 species are found,whereby the families Flaviviridae, Bunyaviridae, and Reoviridae with the genera flavivirus, nairovirus, and orbivirus are the most prevalent. Because of their special importance Omsk hemorrhagic fever, louping-ill disease, tick-borne encephalitis, and Crimean-Congo hemorrhagic fever are discussed in detail. Although West Nile virus is mainly transmitted to man by mosquitoes, it is discussed in detail, because West Nile fever has become a good example for a new and rapidly spreading vector-borne disease in the USA and for a recurrent one in Europe. Secondly, besides the mosquito-bird cycle an interesting tick--bird cycle is emerging. The overview clearly demonstrates that in Europe (particularly in Germany) tick-borne viruses, with the exception of TBE, constitute an extremely ignored research subject. This lack of attention is in contrast to their importance and results in a lack of necessary scientific data.