Things that cause viruses to die include light, a person's immune system, antiviral drugs and vaccines. Recent studies have shown that bursts of purple light from low intensity lasers are enough to kill viruses. The laser damages the outer shell of the virus and eventually kills it.
The healthy tissue around the virus is left unharmed by the laser light, and the virus also doesn't build up a resistance to the laser.
Ultraviolet light has also been shown to kill viruses and is already used to disinfect drinking water and food products. However, unlike laser light, viruses can protect themselves against UV light by mutating. UV light also damages healthy tissue. Light activated rhodium also shows promise in killing viruses, as does applying a virus-killing substance to materials.
Viruses can also be killed by antibodies from an organism's immune system. These antibodies adhere to the virus and destroy it. Killer T-cells also seek and destroy viruses. A hormone such as interferon controls the virus by killing the cell it has infected as well the cells around it.
Vaccines work by stimulating the body into attacking weakened or killed viruses. The body then recognizes the virus and attacks any live examples in the future. Antiviral drugs feed the virus false DNA building blocks which the virus can't use.