|Gene therapy. Image Wikipedia|
Viruses are very good in making cells produce things (namely proteins) "to order."
That's what they do. Think of them as an invading army. They take control of the resources, rape the women ... Viruses inject their own instructions into the cells, making them do their bidding.
However, with non-virulent viruses, this ability can be used to get cells to make proteins the body needs and lacks the coding for.
An example is the treatment of hemophilia in dogs.
Dogs with hemophilia have a deficiency of a specific protein with results in severely reduced ability of the blood to clot. There can be other causes but generally hemophilia is an inherited disorder that results from a flawed gene.
The virus delivers a functional version of the gene and the cells are back in business.
Only a small number of dogs have been treated with this therapy so far and the immune system might not always be happy with the idea. So there are some concerns.
But it is certainly an intriguing field of research.
Gene Therapy: Renewed Hope in the Treatment of Disease?
Clotting Deficiency (Inherited) in Dogs
Cell and Gene Therapy
Platelet-targeted gene therapy with human factor VIII establishes haemostasis in dogs with haemophilia A