Prior to Columbus’s voyage to the New World in 1492, scholars estimated that the population of the Americas was around 30 million people.
By the mid-17th century, more than 90 percent of the continent’s indigenous people had perished, largely due to exposure to diseases that migrated westward with European colonizers.
Examples of such diseases include smallpox, influenza, measles and pertussis. This exchange of pathogens went both ways, however. Europeans brought virulent strains of syphilis and tuberculosis to the Old World from the Americas. Some have described a “Columbian Exchange” in which diseases propagated in both directions across the Atlantic Ocean.
Rheumatoid arthritis arrived in Europe after the Age of Discovery. Native North American tribes, including the Pima Indians, manifest high rates of rheumatoid arthritis. Could a pathogen be involved?
The late rheumatologist T. McPherson Brown popularized treatment of arthritis with antibiotics decades ago. He even treated Tamoka, a gorilla then alive at the National Zoo in Washington, D.C. As a Rheumatology Fellow at Georgetown University, I visited the same zoo, and worked with veterinarians to describe some cases of arthritis in monkeys. Perhaps more gifted researchers, using sophisticated laboratory technologies, will eventually shed light on the relationship between bacteria and arthritis. As a corollary, we might learn if migration patterns among humans played a role in spreading causative infectious agents.
In the case of rheumatoid arthritis, explaining underlying causes is also complicated by additional public health observations. For example, smokers seem to suffer a far greater risk of RA than nonsmokers. Moreover, as smoking prevalence declined in society, RA rates have also declined. Could smoking result in bacterial infections that “light up” a disease process leading to a secondary arthritis? We know that RA involves an inflammation and destruction of joint tissue, and it is possible that the human body attacks the joints in RA as innocent bystanders.
RA patients elaborate specific “anti-CCP” antibodies, lending credence to this possibility. Smoking tobacco products, of course, is a Native American cultural phenomenon that spread worldwide in the centuries following Columbus’ voyages.
The obesity epidemic is another noninfectious phenomenon that is spreading worldwide at an alarming rate.
Although rates of obesity are as low as 2 percent in rural India and 3 percent in Japan and Korea, even these countries are seeing trends towards increased body mass, particularly in urban centers. Sub-Saharan Africa has seen obesity rates double in 15 years, to a still modest 10 percent rate.
These trends towards obesity reflect the influences of global economic development. For example, about half of Chinese persons perform heavy manual labor at present, compared to two-thirds a generation ago. Moreover, as exercise levels fall, diets are increasingly rich in calories in most countries. Among Europeans, the Norwegians boast an obesity rate of only 8 percent, but nearly a quarter of Britons tip the scales at a rate consistent with obesity. Americans are at the top of the list of industrialized nations, at 31 percent obesity rates. Among traditional populations of Oceania, however, including the inhabitants of Nauru and Samoa, obesity rates are as high as 94.5 percent, perhaps reflecting cultural attitudes that equate largeness with beauty and wealth. It is clear that the advent of global economic development is coinciding with an epidemic of over-nutrition that threatens public health.
Our interconnected world economy allows diseases to travel the globe more easily than ever before. The obesity epidemic reminds us that changing patterns of diet and behavior can take hold throughout the planet. If humans succeed in exploring other planets, I suspect a new disease will be described. As an example, we are already learning that prolonged weightlessness can induce thinning of the bones and muscle weakness.
Scott T. Anderson, M.D., Ph.D. (email@example.com) is clinical professor of medicine, UC Davis. This column is informational, and does not constitute medical advice.