Wherever there are people, there is disease. This seems like a “truism” — something that should go without saying and is just a part of life — but, when you think about it, there really is no reason for there to be disease among us. Injuries and conditions that rise from genetic abnormalities, sure, but infectious disease? Humans have some of the most complex brains, capable to landing men on the Moon with nothing more than a slide rule and the computing power of a modern microwave oven. So why is it that we can’t overcome the very simple virus or the slightly more complex bacteria?
One of the many answers to this is human nature itself. It is human nature to get up and leave from a situation that becomes dangerous. We have two legs and intelligence, and we use them to escape danger and go where there is prosperity and opportunity. International borders, even those that are fortified, are easily overcome by ingenuity and tenacity. Some borders are even overrun by sheer numbers. And, with people come diseases.
We have become so good at getting up and getting going that we can be in any part of the world within 24 hours thanks to any of the many modes of transportation we have devised. A plane could take off from the Democratic Republic of Congo with an Ebola-infected person right this moment and land in Denver, Colorado, before any of their symptoms start to show. Planes, trains and automobiles carry people, and people carry diseases.
Back in the middle ages, ships traveling from Asia to Europe carried with them bubonic plague (aka “The Black Death”). The bubonic plague is a bacterial infection with Yersinia pestis, and it can be transmitted through the air (if the infectious person has the pneumonic kind) or a bite from a flea carrying the bacteria. In Europe and other places in the known world at the time, it is very probable that both kinds of transmission happened. By the time it was all said and done, more than half of Europe’s residents had died.
In the 1500s, as more and more Europeans invaded and explored the Americas, they brought with them several diseases that would be new to the Native American populations. Remember, the land bridge between Asia and North America had been gone for thousands of years by the time Columbus arrived in the Caribbean. In that time, Rinderpest — a relative of measles happening in cattle — had mutated into measles, a human infection, around 1100 CE. Smallpox, one of the oldest viral infections known, is about 10,000 years old, younger than the land bridge at the modern-day Bering Strait. In the few remaining historical records from before the arrival of the Europeans, there is little to no mention of anything resembling these and other infectious diseases. This meant that Native Americans were not immune to, or even experienced in controlling, many of the diseases presented to them during the conquest of the continent.
More recently, economic and safety conditions in Central America have forced thousands of people to make the long and difficult trip north through the jungles of Central America and Mexico, the gang-controlled cities of Mexico, and into the desert and plains of the border with the United States. While countries in Latin America are very good at immunizing their populations, some diseases are making an appearance along with the migrants. In Mexico in the last few weeks, immigrants awaiting asylum decisions from the United States have experienced a sizable outbreak of chickenpox at border housing facilities.Unlike in the United States, countries in Latin America do not immunize against chickenpox (varicella). There have also been reports of diarrheal diseases and, during the winter months, respiratory illnesses. And these cases are crossing the border one way or another and triggering their own small clusters of disease within the United States.
Then there are the vaccine-hesitant or vaccine-refusers who travel (themselves or their unvaccinated children) to places around the world where measles is active, like the Philippines, Europe and Madagascar. They then get infected and bring back measles into their communities, many of which are low in their measles vaccine coverage. This has been the cause of the current epidemic of measles in the United States, and epidemic that threatens the “eliminated” status of measles in the country if it is not brought under control soon.
As you can see, diseases travel, but they don’t travel alone. They travel with us. Even with our big brains, we can’t seem to bring them under control, and those same big brains allow us to find ways to get from point A to point B and around any kind of border or barrier to travel. Those big brains also have created the science and technology that goes into immunization. Rinderpest in cattle and smallpox in humans have been eradicated, meaning that there are no more cases of either infection happening in the world today. Polio is very, very close to eradication, too. Measles is next on the list, even with the current resurgence of it worldwide. It’s going to take work and brains to finish the job and move on to defeating other maladies.