Animals that changed the world : disease carriers.

Illnesses transmitted from animals to humans have changed the world. The tsetse fly, by causing sleeping sickness in cattle and humans, slowed all development in Africa. Malaria protected West Africa from western colonial invasion. In South America, Chagas' Disease affects 16m people. Typhus, transferred by the lice on rats, killed many in Napoleon's army in Russia, and again at the end of WW1. Most common diseases originated in domestic animals, and BSE is a recent example. But diseases such as smallpox and measles, carried by Europeans to other parts of the world in the past 500 years, have killed the most people - e.g. about 95% of native Americans - because they have had no genetic resistance to the new diseases.