Guns Germs And Steel

What a coincidence, I was just reading about how major diseases faced by humans are contracted due to close association with domesticated animals. Ever since certain animals are domesticated, their inclusion into our lives are a mixed blessing, on one hand they guarantee a source of food, security and companionship. On the other, they also transmit a host of diseases which could explode into epidemics.

A list of some human diseases and their sources
Measles - Cattle (rinderpest)
Tuberculosis - Cattle
Smallpox - Cattle(cowpox or other livestock with related pox viruses)
Flu - pigs and ducks (think avian flu)
Pertussis - pigs, dogs
Falciparum malaria - birds

These diseases thrive best in a human population that is sufficiently large and concentrated (which is a characteristic of a farming society.
In fact, Jared Diamond proposed that major diseases associated with dense populations and domesticated animals have a crucial role to play in history. These diseases have wiped out large numbers of native Americans who had no previous exposure (and thus no immunity) and allowed an easier conquest by the Europeans. For example, in 1520, an infected slave carrying small pox wiped out almost 50% of the Aztecs in Mexico. This paved the way for an easy conquest of the Aztecs by the Spaniards. By 1618, Mexcio’s initial population of 20 million had plummeted to 1.6 million. And small pox was a disease transmitted to humans via cattle.

See Jared Diamond's Guns Germs and Steel