Evidence of a New World Origin for Canine Distemper

Measles virus (MV), rinderpest virus (RPV) and canine distemper virus (CDV) are important, highly homologous morbillivirus pathogens, with unclear evolutionary relationships. Historical records, epidemiological features, paleopathological evidence, and comparisons of codon usage efficiency were examined to investigate the origin of CDV. The first definitive description of canine distemper was made in 1748 by a Spanish scientist traveling in South America. In contrast, both historical and molecular analyses have traced MV and RPV to the 10th–12th centuries. MV was introduced to the New World in the 1500s, while RPV was not reported in the Americas until the 1920s. To investigate when CDV arose in the New World, over 100 canine skeletons dating to pre‐European contact were examined for enamel erosions, which are evidence of endemic CDV infection. None were found. Analysis and comparisons of codon usage bias revealed that the human codon usage pattern is more efficient for all 8 of the CDV proteins than either canine or bovine codon usage patterns (p<0.001). The historical, epidemiological, paleopathological and molecular evidence supports the hypothesis that canine distemper arose in the New World from MV after the European conquest.