Emergence of "new" viral zoonoses.

In the last two to three decades a significant increase of viral zoonotic i nfections was observed. These zoonoses are not only newly (or previously un recognized) emerging diseases, but also due to the reappearance of diseases thought to have been defeated (re-emerging diseases). "New" viral diseases can arise when viruses broaden their host-range (monkey poxvirus; equine m orbillivirus), or can be a consequence of intrinsic properties of the virus itself, such as high mutation rates (influenza A virus). Most new or reeme rging viral zoonoses are due to infections with hemorrhagic viruses. Many o f them are transmitted by insects (arboviruses, e.g. yellow fever virus) or by rodents (e.g. Hanta viruses), others by contact with patients and nosoc omial infections (e.g. Ebola virus). The emergence and increase of these di seases are a consequence of anthropogenic environmental changes, such as di stortions of the ecological balance and changes in agriculture. In addition , the uncontrolled growth of the cities in tropical and subtropical regions without improvement of the public health measures and the increasing inter national animal trade and travel also favour the spread and recurrence of t hese diseases.