Infection with CDV occurs by inhalation with the virus localizing in tonsils and bronchial lymph nodes. After 2-5 days there is a cell associated viremia, with the virus infecting lymph nodes, spleen, thymus, bone marrow, and macrophages in the lamina propria of the stomach and intestine. At this stage of infection, severe depletion of lymphocytes may develop with concomitant immunosuppression. The brain is sometimes affected, usually after the visceral infection has ended. The virus first infects macrophages in the meninges and later spreads to ependymal cells, glial cells, and neurons.
Neuronal involvement leads to behavioral changes and varying degrees of muscular spasm or paresis.
Forty to sixty days after apparent recovery, some dogs develop demyelinating lesions within the brain. This complication of CDV infection is usually fatal. Morbilliviruses possess two proteins which facilitate binding to host membranes, hemagglutinin and F protein. The F factor mediates fusion of the viral envelope with the cellular membrane and assists in viral attachment. It also causes host cell fusion and is responsible for the formation of syncytial cells.