[header] How to diagnose canine distemper [title] Notice if your dog becomes feverish and loses his appetite. [step] Once your dog has contact with the virus, it may incubate in his body for three to six days. Your dog may become feverish, lose his appetite, and have general head cold symptoms like a runny nose. 
He may also appear slightly off color or noticeable ill. [substeps] Blood tests taken at this time would show a dip in his white cell count, as his body is using up white cells to fight off the infection.