Diagnosis of Canine Distemper
Blood tests usually are not helpful in the diagnosis, though in some cases they may reveal lymphopenia (a deficiency of lymphocytes, a type of immune system cell) during early infection, followed by leukocytosis (an increase in the number of white blood cells circulating through the blood) during later infection.
Imaging studies (e.g., x-rays, CT scans) can diagnose pneumonia.
Inclusion bodies (unique cellular structures that indicate the presence of the virus) can be detected with microscopic examination of buffy coat cells (cells that make up the "buffy layer" of centrifuged blood) and conjunctival secretions (secretions from the conjunctiva, the inner lining of the eyelids). A negative result does not rule out the possibility that the dog has distemper.
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.
Polymerase chain reaction (PCR), a technique that helps identify the virus's genetic material, 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.
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.
Canine Distemper Differential Diagnosis
Many diseases can cause symptoms resembling canine distemper and should be ruled out during diagnosis. Respiratory symptoms (e.g., cough and labored breathing) could be caused by bacterial pneumonia. Intestinal symptoms (e.g., vomiting and diarrhea) could be caused by gastroenteritis (an inflammatory bowel disease). Seizures and other neurological symptoms could be caused by toxoplasmosis (a protozoan infection) or epilepsy.