The latest Ebola outbreak has elicited a lot of fear—justifiably so. The potential for a pandemic highlights the critical need for epidemiologists to understand the origin and spread of human pathogens.
The Ebola scare also raises difficult questions of a theological nature. How could a good God, who is all-powerful and –knowing, create a world where human disease is so rampant? How do Christians explain the origin of infectious agents that plague humans? A new study by a large team of international collaborators helps address these concerns.1
The researchers studied the origin and spread of tuberculosis, choosing to focus their investigation on how this disease spread to South America. This insight is important because tuberculosis is on the rise worldwide. Any understanding into the spread of tuberculosis will also help scientists understand the potential avenues for the spread of diseases like HIV, MERS, SARS—and Ebola.
The strains of Mycobacterium tuberculosis (the infectious agent that causes tuberculosis) found in South America bear genetic similarity to those isolated in Europe. Presumably, European colonists introduced these strains to Native American populations beginning around the early 1500s. However, anthropologists unearthed a number of human skeletons in South America that show evidence of a tuberculosis infection dating well before Europeans made contact with Native Americans. Did tuberculosis travel with humans when they migrated from Asia into the Americas? It’s not likely because the genetic diversity of global M. tuberculosis isolates indicates that these human pathogens originated in Africa only 6,000 years ago and humans crossed from Asia into the Americas via the Bering land bridge around 14,000 years ago.
To help identify the source of pre-contact tuberculosis in Native Americans, the research team isolated ancient M. tuberculosis DNA samples from the skeletal remains of three humans that date between 750 and 1350 AD (before Europeans made contact with Native Americans). The genetic signature of these ancient DNA samples matches M. tuberculosis DNA isolated from sea lions and seals. This finding implies that sea mammals harbor pathogens that can be transmitted to humans (via a process called host-hopping or zoonotic transfer) and can spread these pathogens around the world as these creatures migrate across the oceans.
This insight could help our efforts to prevent the introduction of new pathogens into the human population and contain the spread of pathogens that are already introduced. This work also helps explain, in part, how a God who is all-good, -powerful, and -knowing could create a world where human disease exists. It seems reasonable to think that when God created humans, he did not create human pathogens. But once humans left the Garden of Eden, they were exposed to animals that did harbor infectious agents and by zoonotic transfer pathogenic viruses and bacteria made their way into the human population.