Once again, Jack, great appreciation to you and your daughter.

I was googling and found 3 things: there was a captain of artillery who was hospitalized for the same Int Febris for a month about the same time and place.

The other is "Febris intermittens (septic temperature) - temperature swiftly raises to 39°C, swiftly falls below 37°C, in 24-hour period the difference of the maximum and minimum temperatures is bigger than 1°C"

Doesn't that sound just like malaria?

And this:
"The health of the Army of the Potomac at its camp along the Rapidan River during the first months of 1864 was relatively good. With the weather unusually cold, most of those who were sick suffered .... Once the campaign was underway, however, malaria and digestive complaints began to haunt the Army of the Potomac. More patients suffered from these problems than from gunshot wounds. It is likely that many of those with other diseases had malaria as well-McParlin commented that he had observed a periodicity, or regularly repeating pattern, of fever in most of his sick during the campaign. The quinine doled out at sick call was undoubtedly vitally important to the fighting ability of Union forces in Virginia."

I wonder if the Confederates were able to get quinine?