With wildlife, we normally administer Albon for 10 days.  The main symptom
I've seen (and smelled) is diarrhea that can't be stopped using
conventional home methods (plain yogurt, gelatin, Kaopectate, etc.) and it
is incredibly smelly!
 
As far as negative tests go, coccidia is very hard to see in a fecal
sample.  You might test 10 times before it shows up.
 
Taking a baby possum to the vet tomorrow who, I suspect, has coccidia.
Albon usually does the trick!  BTW, her fecal sample came back negative
just last week.  But, I'm pretty sure that's what it is.
 
Katharine
[Posted in FML issue 2769]