Except Othar's plan won't work. As Rodin notes:
Well Rodin is wrong.

There's precedent of Sparks just appearing in places with no history of Sparks before. Until the origin of the Spark and how its inherited is understood killing all the current Sparks is just a temporary stopgap.

You could make the assumption that all Sparks have a Spark ancestor in their family tree and exterminate everyone related to a Spark (Which is a lot of people. For example the former Master of Paris and his vast extended family only some of whom are sparks. Or Ghengis Ht'rok-din founder of the Heterodyne family is clearly at least partially a Ghengis Khan expy. Imagine how many descendants he has that don't know it.) and it still might not even work because we don't know where the first Sparks came from at the start.
Like Agatha suddenly just appered?
I think just about all the sparks we have actual family information on is a direct descendant of another spark.
And looking at just how rare sparks in general are, then im pretty sure that anyone with actual data on the matter could scientifically prove the spark is inherited.

It should also be pointed out, that as we were explained very early on in the comic, then feral sparks are mostly a danger to themselves.
We have directly been told that without education and tools its limited what a spark can do. And they are extremely likely to get themselves killed.

So really, all Other has to do, is to kill all the other sparks, then freeze himself for a decade or so and repeat before offing himself.
That would strike a blow against the spark population that it would likely newer recover from. And sparks would go from being a plague to becomming a nuesance that might wreck a street once every couple of years.

Now im not saying this is an ethical solution to the problem.
But it is one thats likely to work.