Progression

Canine Distemper is a multisystem disease that is spread between animals via respiratory droplets (Murphy et al., 1999).  This disease is most common in puppies but also occures in adults.  Inhaled virus invades the respiratory epithelium and the alveolar macrophages.  By day two it is in the mononuclear cells of the tonsils and bronchial lymph nodes.  The incubation period is3-5 days (Hirsh and Ching Zee, 1999).  During the first week of infection cell-associated virus is spread throughout the body in the blood stream.  It goes to the bone marrow, spleen, thymus, lymph nodes, and macrophages in the lamina propria of the stomach and small intestines (Murphy et al., 1999).  After about eight days the rate of further spread depends on the titre of neutralizing antibodies.  If the titre is high the virus will probably be cleared but if the titre is low it will continue to spread.  With a low eight day titre there is extensive infection of the epithelium in the intestines, respiratory, urogenital tract, skin glands, and eventually the brain (Murphy et al., 1999).  Initially the virus is seen in the brain around the vessels but it later infects the glial cells including the oligodendrocytes and causes demyelination (Murphy et al., 1999).  Rarely recovered animals may relapse, maybe years later, and develop encephalitis, “Old dog encephalitis” (Murphy et al., 1999).  Usually recovered animals develop long lasting immunity to CDV (Hirsh and Ching Zee, 1999).

Virus-Where??		Clinical Signs
Air
Tonsils and brocheal lymph nodes	multiplies in lymph tissue and spreads in lymph system
Thymus, spleen, bone marrow, retropharyngeal lymph nodes		Initial fever, leukopenia, immunosuppression
Intestinal lamina propria and Kuppfer cells of the liver	Mononuclear cell associated VIREMIA
All host tissures including respiratory, GI, urinogenital tract, CNS	1)Good host immune response leads to lots of CDV antibodies, limited illness and recovery	Clinical signs may or maynot be apparant
	2)Poor host immunine response and inadequate antibody production	skin- hyperkeratosis, pustules, GI- vomiting, diarrhea, anorexia Respiratory-URT infections, pneumonia CNS- ataxia, tremors, myoclonus, seizures Other-conjunctivitis, sudden onset blindness, enamal hypoplasia
Improved immune function leads to recovery, if not symptoms progress and the disease is fatal.

Table: Progression of Canine Distemper Virus (modified from Greene, 2006)