HuskyWarrior
i remember seeing a reddit post about this a while back and one of the replies was a guy thinking that Dr. Gero engineered it so Goku was weakened and he could take over the world with the androids or something similar. But i think that it was simply a regular virus on earth due to them having a vaccine about 20 years later so depends on what u think is more plausible/fits with the plot best.
It is never said in cannon where it came from, but seeing that they had a cure in a apocalypic future, it must have hit many people. Enough that they could find a dose 14+ years after he died with 17&18 destroying cities all the time. So it most likely was a dormant virus Goku got during his travels in the original Dragonball.
he got it on yadrat, I think I read it somewhere, possibly at a fanfic, but still... I would NOT do that if I were you, yes mc can meet strong characters, but at what cost, let's stay safe and alive, shall we? plus I'm thinking on him going on a space journey, where whis take an interest in him, so he trains him. Or him finding a shenron wish granting orb somewhere, so he can wish to go to the dragon's dimension for training, just like in naruto with chakra beast summons, where he learns of the dragon resting inside of him was named something majestic, so he befriends it, like naruto and kurama, or like in bleach, the sword tells you it's name, abilities, etc... waddaya think?