Brent Patterson, the Trent University professor who has been tracking local coyotes for the Ministry of Natural Resources, has answered this for Friends of Sam Smith Park.
"Depending on the year, >70-80 % of the coyotes and wolves we have tested for exposure to Canine distemper have tested seropositive indicating some exposure to the virus. Interestingly, despite high seroprevelance to distemper, and canine parvovirus, incidences of clinic disease are very rare among coyotes and wolves in southern and central Ontario for both diseases. Wesuspect that a high rate of low-level exposure results in most of our coyotes and wolves developing a sufficient immune response so as to prevent them from contracting clinical disease. In essence they become vaccinated through repeated low grade exposures when they’re young. In many cases, these initial exposures likely occur while they’re still nursing and thus protected by their mothers antibodies. So the short answer is that despite frequent exposure we don’t expect canine distemper to problematic for most coyotes in the GTA. They should be able to safely eat all the raccoons they want."