Viruses can become infected and sickened by other viruses.

Viral infections, caused by small microorganisms called viruses that invade
and multiply in large numbers leading to illness, are nightmares for most
of us. Until 2008, most people thought of viruses as disease causing agents
and not organisms that can be diseased themselves. But according to a study
that was published in the journal "Nature" in France in 2008, viruses can
become infected and sickened by other viruses.