The Doc worked a late shift in pedeatrics emergency room last night and got back after she got home. Here's her first take on your question:

"...I think febris int or int febris is an old term for malaria. Int probably refers to intestinal and febris is old latin for fever. Again, this could be a catch-all phrase but presumably a lot of intestinal illness in the pre-AC south is attributable to skeeters, stagnant water and/or humidity. Sure would be fun to have an old textbook with all this terminology. Maybe Walter Reed will have a big garage sale when they relocate to Bethesda next year..."

(Jack's opinions, hereafter) I'm not in the medical business, but from reading a lot of history it is obvious that there is no way to compare today's modern medicine and diagnostic abilities with those primative practices of only a century ago. If I remember correctly, well into the early days of the 20th century, many physicians still learned their trade by apprenticing themselves to a local doctor, following him around and observing...much as many lawyers "read the law" in a senior lawyer's office to learn their trade. Neither profession required university/college training as a mandate.

Growing up in the "swamp country" of southeast Texas (Jefferson County) in the days before air conditioning, malaria was not all that uncommon. We were lucky enough, as were most of our neighbors, to have screens on the windows and doors for cross venilation, suppliment by electric fans. But, one still had to go out doors and in the summer season...particularly after an especially wet period (post hurricane for example) one could be covered by 'skeeters' in a few seconds after stepping out. I had one first cousin who was diagnosed with malaria in grammer school and several neighborhood kids who would occasionally come down with "the fever and shakes" which were referred to as "malaria."

If I remember correctly, Spottsylvania is in the "Wilderness" country of norther VA, pretty swampy and full of bugs...if not malaria, maybe the "galloping trots" from bad water...typhoid, etc. Given the medical knowledge of the 1860s I'd speculate that the attending doctor may have named the symptoms rather than the cause.

Maybe some other folks will have some input on this, as well.