The rats would give soldiers a fever known as Trench Fever and it lasted for days and sometimes took months to recover from.
The Fever that the Rats gave the soldiers wasn't usually fatal but it was debilitating for the soldiers and anyone infected with the Trench Fever.
The disease would start with severe pain and then it would be followed by a high fever.
It wasn't only rats that carried the disease either Flea and lice also carried the disease to the soldiers in the Trenches.