Conclusions
Viruses are not necessarily disease agents; on the other hand, viruses currently not associated with disease may not be that harmless. Viruses and their hosts co-evolve, which has lead to more successful viruses in the face of improved host defence mechanisms. New and better vaccines are needed but should not be developed without taking the co-evolution of viruses and their hosts into account. The use of viruses as vectors for gene therapy is not without risks - after all, they are disease agents. However, if treated with respect and studied with care and foresight, they carry the promise of future mediators to improved human and animal health and welfare. Cell cultures and animal models had their glorious dominance in the past and may still be valuable in the times to come. However, veterinary virology will continue to play an important role, because animal viruses can be studied in their natural hosts, and creative ideas may spark from this fortunate situation. To speak with James Richard Broughton: "The only limits are, as always, those of vision". The world-wide community of veterinary virologists must combine its knowledge with that of specialists in immunology, molecular biology, gene therapy, and especially with clinicians. Only then will it be possible to achieve things previously thought to be inconceivable. To conclude with another quote, by Robert Kennedy: I wish that you may dream of things that never were, and ask why not?

Acknowledgments
Special thanks to all those who took their time to talk to me about their views on virology, particularly to Ernst Peterhans, Bernard Roizman, Cornel Fraefel, David Paton, Esteban Domingo, Etienne Thiry, Hans Koblet, Luis Enjuanes, Marian C. Horzinek, Mark Suter, Peter Nettleton, Ricco Wittek, Robert Webster, Robert Wyler, and to the many participants in discussions after my presentation of these thoughts at the International Congress of the European Society for Veterinary Virology (ESVV) in Brescia, Italy (2000).

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