Diagnosing the Disease

Difficulty with Diagnosing
Diagnosis can be difficult and is based on the dog's vaccination history, clinical symptoms, and laboratory tests. Blood tests usually are not helpful in the diagnosis, though in some cases they may reveal Lymphopenia, or a deficiency of lymphocytes, a type of immune system cell during early infection. This is followed by Leukocytosis, or an increase in the number of white blood cells circulating through the blood, during later infection.

Indicators of the Virus
Testing for the following may help determine if the virus is present.

Imaging studies such as X-rays or CT scans can diagnose pneumonia.

Inclusion Bodies
Inclusion bodies are unique cellular structures that indicate the presence of the virus. They can be detected with microscopic examination of buffy coat cells. Buffy coat cells make up the buffy layer of centrifuged blood and conjunctival secretions. Conjunctival secretions are from the conjunctiva, the inner lining of the eyelid. A negative result does not rule out the possibility that the dog has distemper.

Viral Antigens
An immunofluorescent assay can detect viral antigens (proteins that the immune system manufactures to fight the virus) in the buffy coat cells and conjunctival secretions when inclusion bodies are not visible. Immunofluorescence involves using special proteins labeled with a fluorescent chemical that bind to the antigens and make them visible. Again, a negative result does not rule out the possibility that the dog has distemper.

Viral Inclusions or Immunofluorescence
Polymerase Chain Reaction (PCR) is a technique that helps identify the virus's genetic material and is usually more sensitive than either microscopic examination for viral inclusions or immunofluorescence. It can be a difficult procedure and it is not always successful.

Antibodies & Elevated Levels of Proteins
Cerebrospinal fluid (CSF) can be examined for CDV-specific antibodies and elevated levels of particular proteins and cells that indicate the presence of the virus.

Differential Diagnosis
Many diseases can cause symptoms resembling CDV and should be ruled out during diagnosis. Respiratory symptoms such as cough and labored breathing could be caused by bacterial pneumonia. Intestinal symptoms such as vomiting and diarrhea could be caused by gastroenteritis, an inflammatory bowel disease. Seizures and other neurological symptoms could be caused by a protozoan infection called Toxoplasmosis or by epilepsy.