Wild animals are a source of many pathogens that might infect us, but the reverse is also true: we and our domestic animals harbor diseases that can devastate wild populations.
    
The canine distemper virus, carried by domestic dogs, has decimated populations of lions in east Africa and harbor seals in Scandinavia. People have inadvertantly caused the death of mountain gorillas (from measles) and chimpanzees (from polio).

Cattle imported to the horn of Africa in the 1880s carried a measles-related virus called rinderpest. Within 10 years, rinderpest had swept through the continent, afflicting gazelles, giraffes, wildebeest, and water buffalo. Carnivore populations plunged as their food supply shrank.

Rinderpest re-emerged at intervals during the 1900s, finally leaving for good when a vaccine against it was developed midcentury. Although only domestic cattle were vaccinated, the virus also disappeared from wildlife—showing that domestic cows were the "reservoir" from which the virus attacked wild species.

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