Come To France!
All you lice and other diseases, French trenches are where its at. Why stay wherever you are when the conditions here are ideal - dark and damp. Dysentery is here and is loving it. It's also a great place to come because combined with the ideal conditions, they can never quite get rid of lice even when they have their special delousing baths and clothing washes. It can also get very wet, because they're in a hole so the rain just falls on them and fills up the trench. Trench foot would especially love it there. There is great eating for all you rats too. The corpses of the soldiers are just left there, waiting to be eaten by you. They ship in literal tons of food daily, 3,240,948 tons in all by the end of the war, so even without eating people you rats can have a good meal! So come to France all of you! You'll love it!