When farmers found out they could spread manure to use as a fertilizer they killed two birds with one stone, so to speak. Eliminating the problem of human and animal waste buildup as well as getting an incredible crop was very fortunate indeed. A process that is still used to this day.
I think the world is filled with scenarios like this, but it's up to us to find out what they are.
I think it should be possible to cure leukemia with H.I.V. (Aids) and vice versa. With leukemia there is a problem of an over abundance of white blood cells that take over the body, and with H.I.V. there is an issue of not enough white blood cells.
This seems like it's too good to be true, but if you look at each way both viruses kill you it does make perfect sense that these two diseases would cancel each other out. Therefore, eliminating the problem.
I'm not sure if the type of combination matters or not, does one have to be a virus and another a disease? There has to be more examples out there of the symptoms of different diseases and viruses that would cancel each other out if they were introduced to each other. I don't have enough knowledge of either topic to know.
So, I just took my own advice just now and googled my above topic, and sure enough H.I.V. and leukemia do not like each other at all. Here is a link: https://www.sciencedirect.com/science/article/pii/S0929664613000612
If there is one of example of a virus cancelling out a disease there must be others out there. Maybe you know of a few?
Scott Goerz