The dragging of smallpox/yellow fever-infested blankets seems a little remote in the line of possibilities. The best biological weapon during the Civil War was always the common soldier in camp with his many illnesses.

I did find some information about the attempt to use chemical warfare during the Civik War. According Jeffrey K. Smart in "HISTORY OF CHEMICAL AND BIOLOGICAL WARFARE: AN AMERICAN PERSPECTIVE,"

"During the American Civil War, John Doughty, a New York City school teacher, was one of the first to propose the use of chlorine as a chemical warfare agent. He envisioned a 10-in. artillery shell filled with 2 to 3 qt of liquid chlorine that, when released, would produce many cubic feet of chlorine gas. If the shell should explode over the heads of the enemy, the gas would, by its great specific gravity, rapidly fall to the ground: the men could not dodge it, and their first intimation of its presence would be by its inhalation, which would most effectually disqualify every man for service that was within the circle of its influence; rendering the disarming and capturing of them as certain as though both their legs were broken...

Doughty’s plan was apparently never acted on, as it was probably presented to Brigadier General James W. Ripley, Chief of Ordnance, who was described as being congenitally immune to new ideas. A less-practical concept, proposed the same year by Joseph Lott, was to fill a hand-pumped fire engine with chloroform to spray on enemy troops.

The 1864 siege of Petersburg, Virginia, generated several chemical warfare proposals. Forrest Shepherd proposed mixing hydrochloric and sulfuric acids to create a toxic cloud to defeat the Confederates defending Petersburg. Lieutenant Colonel William W. Blackford, a Confederate engineer, de-signed a sulfur cartridge for use as a counter-tunnelling device. The Confederates also considered using Chinese stink bombs against the Union troops. Elsewhere, the same year, Union Army Captain E.C. Boynton proposed using a cacodyl glass grenade for ship-to-ship fighting.

Other than possibly Blackford’s cartridge, none of the proposals were used on the battlefield."

John