Diagnosis commonly is made on suspicion, based on the clinical signs and vaccination status of the dog. An unvaccinated dog that comes into contact with an animal carrying canine distemper is likely to develop the virus since the disease is so infectious.
However, scientifically concluding the presence of canine distemper is difficult and takes time as well as complex diagnostic tests. One test, called serology, detects antibodies made by the dog's body to fight the virus. The accuracy of this test is questionable, though, because true exposure cannot be distinguished from vaccine exposure. This is because the distemper vaccine causes the dog's immune system to produce antibodies to the distemper virus, just as natural exposure does.
Another option for the veterinarian is to take a sample of cerebrospinal fluid that surrounds the brain and spinal cord, and then submit this fluid to a laboratory to determine the presence of antibodies to the virus. Occasionally, in special blood smears and tests of certain tissues, the viral antigen or viral material may be detected. Diagnosis also can be made after an animal dies or is euthanized and tissue samples are studied for evidence of the virus.
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