Almberg ES, Mech LD, Smith DW, Sheldon JW, Crabtree RL (2009) A Serological Survey of Infectious Disease in Yellowstone National Park’s Canid Community. PLoS ONE 4(9): e7042. doi:10.1371/journal.pone.0007042
The authors found that the majority of Yellowstone wolves had been exposed to a number of different viruses (evidence from antibodies in blood samples).
They also found evidence for historical outbreaks of canine distemper virus in wolves, coyotes and red foxes in 1999 and 2005. These outbreaks correlated with peaks in wolf pup mortality.
This evidence suggests that wolves have no mechanisms for avoiding the spread of these viral diseases. Perhaps periodic episodes of increased mortality are the price that has to be paid for a longer-term 'herd immunity'?
Edit - in response to OP comment below:
The data indicate very high levels of seropositivity to the viruses. I would say that 'not 100% successful' is an understatement. But I must admit that I am way out of my area of expertise here!
From the abstract:
We found high, constant exposure to canine parvovirus (wolf seroprevalence: 100%; coyote: 94%), canine adenovirus-1 (wolf pups [0.5-0.9 yr]: 91%, adults [>or=1 yr]: 96%; coyote juveniles [0.5-1.5 yrs]: 18%, adults [>or=1.6 yrs]: 83%), and canine herpesvirus (wolf: 87%; coyote juveniles: 23%, young adults [1.6-4.9 yrs]: 51%, old adults [>or=5 yrs]: 87%) suggesting that these pathogens were enzootic within YNP wolves and coyotes.