A primary reason is that viruses do not possess a cell membrane or metabolise on their own - characteristics of all living organisms. Examples of common human diseases caused by viruses include the common cold, the flu, chickenpox and cold sores.
In the past spacecraft have taken greatly different amounts of time to make it to Saturn. Pioneer 11 took six and a half years to arrive. Voyager 1 took three years and two months, Voyager 2 took four years, and the Cassini spacecraft took six years and nine months to arrive. The New Horizons spacecraft took a short two years and four months to arrive on the scene.
| Cool Cosmos. How long it would take to get to Neptune from Earth would depend on the path chosen and on where Neptune and Earth were in their orbits when the mission was launched. For example, the Voyager 2 spacecraft was launched on Aug 20, 1977 and it reached Neptune on Aug 24, 1989.