Diagnosis




Distemper

Differential Diagnosis

Clinical signs such as fever, respiratory signs, neurological signs, and hyperkeratosis are characteristic of a CDV infection.  However, dogs infected with canine hepatitis, herpes virus, parainfluenza, and leptospirosis present with similar signs.  Therefore, further investigative tests are required in order to make a definitive diagnosis.

CBC

Early in the infection a lymphopenia may be observed.


Microscopy/Electron Microscopy

At necropsy, histologic lesions (eg. intracytoplasmic inclusion bodies) can be found in bronchial cells, gastrointestinal cells, leukocytes, and cerebrospinal fluid.

Intracytoplasmic
Necrotizing bronchiolitis with large number of neutrophils.  Two arrows point to intracytoplasmic eosinophilic inclusion bodies in the bronchial epithelium (hematoxylin and eosin stain).

Gross lesions include a very small thymus in young animals, lungs characterized by interstitial pneumonia, occasional hyperkeratosis of the footpads and nose, and mucopurulent discharges from eyes and nose.



Immunohistochemistry

Immunofluorescence & Immunohistochemistry

Immunofluorescence and immunohistochemistry are used for detection of CDV antigen.  Post- or ante-mortem viral antigen may be detected in tissues such as conjunctival or vaginal imprints, and respiratory or footpad epithelium.  These samples may be negative in an immunofluorescent assay when the infected dog is showing neurological signs exclusively or when circulating antibody is present.  In this case, serology can be used to make the diagnosis.



Immunohistochemistry for CDV antigen in a) nasal mucosa b) footpad epithelium c) haired skin of neck





Serology

The presence of viral specific IgM or an increased ratio of CSF to serum viral specific IgG is indicative of CDV infection.  However, dogs may die without significant antibody production or conversely may have significant antibody circulating equaling that of a vaccinated dog.  Therefore, one must use caution when using serology as a diagnostic tool.


ELISA

Enzyme-linked immunosorbent assay (ELISA) can be used to detect viral antigen in serum or cerebrospinal fluid.


PCR

Reverse transcription polymerase chain reaction (RT-PCR) can be used for detection of CDV RNA in blood cells and urine sediment cells in either an infected animal or a post-mortem animal.  It amplifies and helps to identify viral nucleic acid.  It is said to be more sensitive than immunofluorescence and is a relatively fast procedure.


Imaging

Radiography, ultrasound, and CT scans may be used to diagnose pneumonia associated with CDV.  Brain changes typically cannot be seen.


Pneumo

Lung radiograph from dog recovering from CDV-associated pneumonia