Discussion about the requirement can be read in the [[ https://trac.wildfiregames.com/ticket/1912 | Trac ticket ]].
@fatherbushido suggested to follow this approach: "flaming projectile 'ignites' (or a poisonous one poisons) the target which suffers damage for a while regardless of running away."
Nice nomenclature defined on [[ https://dota2.gamepedia.com/Damage_over_Time | DOTA wiki ]]: https://dota2.gamepedia.com/Damage_over_Time which I'd follow in this patch.
This Diff is in work in progress. If you like the approach I can extend it to melee and ranged splash attacks. Sound or animation would be nice because right it's not that visible why the unit is being damaged over time.