HI there and sorry for the bad english.
I have found an bug on the needler sniper gun (i think it is an bug)
the needler toxin is going away after an sniper shot.
Here the discription of the toxin
here an enemy with the active needler toxin:
and after the sniper shot the toxin is deleetet:
And the same on other enemy:
and after sniper shot its gone:
thanks your Bolt Thrower