from Bevan Sawatsky, Sébastien Delpeut and Veronika von Messling writing in The Biology of Paramyxoviruses:
Canine distemper virus (CDV), a member of the genus Morbillivirus, causes one of the most devastating infectious diseases in carnivores. It is highly contagious and transmitted by aerosol or contact with body fluids from infected animals. Immune cells expressing the morbillivirus receptor signaling lymphocyte activation molecule (SLAM, CD150) are the initial CDV targets, and first infected peripheral blood mononuclear cells are detected after two days. Infection of epithelia coincides with the onset of clinical signs, and is frequently followed by neuroinvasion and neurological sequelae. Disease severity can range from mild and short-lived to lethal, depending on strain and sensitivity of the host species. Therefore, the commercial live-attenuated vaccines, even though they are safe and efficacious in dogs, have to be carefully evaluated for each species. The characterization of genetic virulence determinants has revealed the importance of efficient entry and viral interference with innate immune activation, which constitute starting points for the development of the specifically attenuated vaccines.
Further reading: The Biology of Paramyxoviruses