They are the only nuisance one cannot turn off in sandbox mode... I know not to accept Nostros, so the trouble is most likely restricted to Memaus infecting peeps.
From your link here you can adjust the
Find the default mood, MOOD_INC_DEFAULT and set the body value for
Find the mood entries MOOD_AT_BIRTH and MOOD_AT_BIRTH2 and set the
Skrashers spawn with a tiny amount of health that fades away almost instantly so they die straight after appearing...
Not a real answer to your question, I admit, but they've never been a real problem for me.
Just build lots of Scuzzers Mk II or III (really cheap after researching them properly) and a Recycler every few sections. With the e the Recycler extracts from the garbage, they pretty much pay for themselves.
Also place lots of Litter Bins, in particular next to everything that produces garbage.
I found the MEMAU_TARGET_LEVEL setting, described here, but still sometimes Skrashers show up.