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Many factors led to the situation in which we fear the appearance of yet another exotic microbe simply demonstrating our vulnerability to new invaders and the shrinking of the globe. Beside the tremendous increase in international travel and trade, climatic changes are a crucial factor for exotic arboviruses to establish endemic transmission cycles in Europe. Certain temperatures, humidity and--at least for mosquitoes--suitable water bodies are required for the respective species to develop and become abundant. Increasing temperatures reduce the overall time of the mosquito life cycle because the aquatic developmental stages are completed faster, and secondly, the time span required for the mosquito to be capable to transmit the acquired arbovirus to another susceptible host is shortened. Thus the chances for an exotic arbovirus to establish an autochtonous transmission cycle are increasing. Here, a review is provided on the known factors that determine vector competence for mosquitoes and a particular arbovirus. The comparison of the closely related West Nile and Usutu viruses in Europe and North America further demonstrates how different and unpredictable the epidemiology of such arboviruses can be. Time will answer the question on who is going to be the next arboviral intruder into Europe. But it is today that we can bring ourselves into a good position to conquer the next "alien" by setting up interdisciplinary networks to promote research on these "exotic" and thus neglected pathogens thereby enhancing our understanding on their transmission and the factors and mechanisms required for this.

In this case report we discribe clinic, pathology and diagnostic of an avian reovirus-infection in pheasants. The disease was observed 1993 in a flock of game-pheasants in the western part of Turkey. Of a live-stock of 100 animals, 27 were affected most of them being three to five months old. Beside a general disorder, sick pheasants showed signs of shortness of breath as well as greenish, watery diarrhoea and died within a week. The pathologic findings were dominated by an extreme hepatopathia. In addition a fibrinous tracheitis, a catarrhal inflammation of the gut and a perihepatitis fibrinosa could be observed. From organs of affected pheasants a pathogen could be isolated, which was characterized anti-genetically, by physico-chemical properties an by electronmicroscopy as avian reovirus.

2238 sera of bovines, 95 of goats, 251 of antelopes (various species), 143 of zebras and 11 of warthogs collected in Tanzania as well as 811 sera of men and females of the city and the region of Dar es Salaam were tested for haemagglutination inhibiting antibodies (Ab) to reovirus serotypes (St) 1, 2 and 3. Ab to St 1 resp. 2 could be detected in 24--39% of bovines, goats, antelopes and zebras, and in warthogs to 64%. In human beings the positive percentage was 60%. Ab to St 3 were most prevalent: Sera of domestic animals were positive in 70--84%, of wild animals in 77--100% and of the human population in 91%. These figures include the occurrence of Ab to one St alone as well as to more than one St. A further analysis showed, that Ab to St 3 are definitely dominant especially in sera of animals, whereas the simultaneous occurrence of Ab to all 3 St was more frequently observed in sera of human beings. Other Ab-type combinations were apparently of far less importance. It seems to be significant that the highest infection rate was found in humans (except zebras and warthogs) and that their contact to animals did not result in a higher Ab conversion rate as without such a possibility. The results were discussed under seroepidemiologic aspects and it is concluded that reovirus infections are facultative viral zoonoses.