I'm not what you would call a student of the War and cannot recite sources for such, but I've never heard any tales of fever or disease used in a manner that could be described as "weapons" other than in prison camps where medical supplies were intentionally withheld in order for disease to spread through the inmate population. I have heard tales of towns spreading a rumor that an outbreak of fever or disease was present in order to dissuade Union troops from marching through on a pillage and burning campaign. It is said that Lowndesboro was given to detour by Wilson's army in route to Montgomery due to such a rumor.