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The more CDV antibodies in a population, the more black wolves in that group, Cubaynes, Coulson, and their colleagues report today in Science.

Over the next decade, she and her collaborators tallied coat color and disease prevalence—as indicated by the presence of CDV antibodies—in 12 populations of wolves across North America, collecting data on more than 1100 individuals.

"This is not the only cause of death, as all morbilliviruses, including CDV, cause immune suppression in their host, which can lead to secondary bacterial infections, giving rise particularly to pneumonia and in some cases diarrhoea. So, CDV is a pretty nasty disease," she said.

We can't tell what CDV would do to humans, but the fact that in some of the monkey outbreaks, many of the animals died should give us some cause for concern.

Some think that continued use of the measles vaccine might be sufficient to protect against a possible jump into humans by CDV, but Prof Cosby isn't as convinced: