The Aztec virus spread with terrifying speed and killed as many as 17 million of the population, but very few of the Spanish colonisers fell victim to the disease.
Professor Todd Disotell thinks that the Spanish, being more genetically diverse than the early Americans, had a greater immunity to viral invaders. However, Mexican epidemiologist Rodolfo Acuna Soto makes a discovery that casts doubt on whether genetic characteristics are the sole solution to this puzzle. He has identified a group of Spaniards who did die from the disease: Priests.