I. Introduction Parvoviruses belong to the large group of viral agents of which virologists have become aware by chance in many biological materials due to the availabil ity of more sensitive isolation techniques and the extensive use of the electron microscope. In general, many of these viruses lacked the stimulating background of an infectious disease and, therefore, have fallen into oblivion already soon after discovery. In case of parvoviruses, however, interest has been maintained because of the circumstances under which most of them were isolated. A great number of parvoviruses has been recovered from tissues of tumor bearing animals, from cell-free filtrates of tumors, or from stable cell lines of tumor origin. These observations necessarily suggested the newly isolated viral agents of playing an important, yet unknown role in the induction and develop ment of cancer. On the other hand, further parvoviruses were found constantly associated with adenoviruses. It was the experimental analysis of the multiplica tion behaviour which then revealed that the association between parvoviruses and tumors or parvoviruses and adenoviruses originates from the basis of a cer tain genetic defectiveness. For some members of the group this may be overcome by cellular helper effects in rapidly growing tissues, for several others, however, by biochemical events in the simultaneously occurring replication of an adeno virus only. Additional points of view in favour of parvovirus research have arisen from experimental animal studies."

Mobility oflarge parts of the human population, whether related to commercial necessity, touristic activities or to migration induced by war and social pressure, carried and carries the risk of spreading infections. Modem air travel effectively circumvents existing quarantine regulations as infected individuals thereby can reach almost every geographic location while stiIl in the incubation phase of the disease. Hence, infections previously restricted to distinet regions due to their strict association with non-human reservoirs or vectors can suddenly surface in non-endemic areas where lacking experience and technical means make clinical and laboratory diagnosis difficult. Excellent examples for such situations are many vector- or rodent-borne viruses but also hepatitis viruses, the human immunodeficiency virus and, last but not least, filoviruses. The following articles are based on papers presented at an international symposium on "Imported Virus Infections" heI d at the Max von Pettenkofer Institute, University ofMunich, Munich, Germany on March 31 to Aprill, 1995. They illustrate today's knowledge on the epidemiology, dynamics of spread, as weIl as the frequently limited possibilities of prevention and therapeutic treat ment of associated disease. Special emphasis was placed on filovirus infections which, as if to highlight the topics of the symposium, reappeared and spread in Zaire in the first half of 1995. The symposium was dedicated to the memory of Friedrich Deinhardt M.D., virologist, professor and director of the Max von Pettenkofer Institute for Hygiene and Medical Microbiology from 1977 unt il he died on April 30, 1992."