Life is an ordered system - in vivo, in vitro, or in silico - that contains information and structure for its function, replication, and evolution in response to its environment. That's all you need.

If it can feel sad, it is intelligent life.

Viruses are packaged information that harnesses more complex systems - a disease of management. That is as primitive as life can be and it still requires better stuff to function. Prions are a thermodynamic disease. They are no more alive than crystallizing salt.

Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf