you need to worm them asap-flubenvet preferably. when I had an outbreak the vet prescribed ivermectin as an emergency measure while I waited for the flubenvet pellets to arrive but be warned, if you treat it expect some losses anyway-by the time they are showing signs they have full grown worms.
I had wormed a month before with the flubenvet premix but I think the hens lower down the pecking order didnt get a good enough dose-besides, wormers are not protective, they only treat what is there at the time.