The pathogenesis of canine distemper was well described by Max Appel (1969). Upon infection by inhalation or ingestion, the virus first invades the tonsils and bronchial lymph nodes. During the first week, the virus spreads to the rest of the lymphoid tissues, including the spleen, thymus, and bone marrow, causing a leukopenia and a transient fever.
Slindee, Char and Carithers, R. W.
"The Demyelinating Encephalomyelitis of Canine Distemper,"
Iowa State University Veterinarian: Vol. 38
, Article 8.
Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol38/iss1/8