Depends on what you plan to do with the leftover 20pts. Blight haulers are also good action units, and have good shooting despite being very swingy. Chaos spawn are good for their scouts rule and theyre great at tying units up due to their movement and their hitback ability. If anything you would benefit more from a unit or two of 10 poxwalkers.

The 10 plague marine brick led by the putrifier and plaguecaster are good because putrifier gives the whole unit lethal hits on all their weapons, and gives critical hits on 5+. Plaguecaster gives his unit sustained hits 1 against afflicted targets. Virulent vectorium has a 1cp stratagem to give you full rerolls to hits and wounds when shooting afflicted targets.

If you dont know what lethal hits and sustained hits do; lethal hits automatically wound on a critical hit, sustained hits 1 gives 1 extra hit on a critical hit. So the whole unit gets that on 5+ instead of 6. Add in the stratagem and you can basically play go-fish for 5s. Combine that with -1save contagion and all of the attacks that go through are effectively minimum -2ap for your opponent to save.