The virus is picked up from the upper respiratory tract by macrophages and subsequently taken to the tonsils, retropharyngeal and bronchial lymph nodes where the virus replicates. Virus replication at these sites is associated with fever. In a period of three to six days post infection, cell associated viremia results in infection of lymphatic tissues and epithelial cells throughout the body. At this point the animal's humoral and cell mediated immune systems may be sufficient for it to recover with or without the infection having become clinically apparent.
Virus shedding begins at the time of epithelial colonization and virus replication.
Multiplication of virus in lymphoid tissue results in a lymphopenia which suppresses the immune system's ability to control bacterial infection. CNS signs may develop acutely or may be mild and slowly progressive as in old dog encephalitis. CDV infection may result in subclinical, or severe illness from which animals may or may not recover. The duration of the disease varies. With moderate control, signs are less severe and the virus may or may not be cleared.