Lydia Kang - Patient Zero - A Curious History of the Worlds Worst Diseases

Ebola virus particles in a colored image from a scanning electron microscope.

As technology progressed, the secrets of our micro-invaders began to be revealed. We discovered nuclear genetic material, or the DNA and RNA that proved to be the blueprints by which these pathogens lived out their fate of latching on to our cells, invading them, and hijacking our base components to make more of themselves. If that werent enough, we figured out that our often invisible tormentors change the rules. Constantly. We tend to think of our speciess origin story as a unique miracle of evolution. But it turns out that bacteria and viruses have been evolving right along with us, often within us, and at a far faster clip than we do.

Part of our investigations of pathogens involve not just the identification of diseases they spawn, many of which have been with us for millennia, but novel invaders weve never seen before. (Or, in the case of diseases like Legionnaires, bacteria that were anonymously picking us off for years until we finally figured out what they were.) Like so many other diseases that came before, we learned the structure of new ones, how their surface proteins attach to ours to gain purchase into our bodies, and how they spread, down to the precise details. It used to take decades to identify a new disease; now it takes days. But a genetic sequence doesnt hold all the answers, and a flurry of questions always remain, like: Is six feet apart enough to prevent a loud talker from spreading COVID-19? How many layers of cotton fabric will prevent passage from a cough? How often must healthcare providers use hand sanitizer during the doffing procedure of personal protective equipment in the hospital?

The pathogens still find a way to get us, of course, but we fight back by figuring out how critically ill patients can be saved and by quickly separating effective medicines from those that are pure quackery (see ). We develop and produce vaccines, sometimes at a dizzying pace, all while dealing with the fallout of information that can be wrong, correct, changeable, frightening, and on occasion, laughable.

But regardless of the social reactions, no epidemic or pandemic arrives without the inevitable questions: How did it start? Why did it spread? And how do we stop it?

Even with the most mundane infection, we must know the nature of its origin. We may have caught something as simple as a cold and, as we hack up phlegm and call in sick to work, the question that nags is: Where did we catch it? Was it the coworker who refused to take a sick day, coughing and snorting in the cubicle next to us? Or when our doctor tells us we have hepatitis C and we later learn it was from a contaminated syringe full of pain medicine we got during an ER visit? Or even when a new disease like COVID-19 arises and upends the lives of billions of people, we still calmly need to know: Who is to blame? From where did it come? Is there a patient zero?

In many cases, we can answer at least the first two components of the disease equation, as more than 60 percent of human pathogens are zoonotic diseases, or those that have jumped from animals to humans. And, tellingly, the vast majority of novel infectious diseases that have emerged in the last seventy years resulted from zoonoses. There is no shortage of theories and explanations for why: Our voracious human appetites have brought us closer to fowl, bushmeat, and wild animals from whence these microbes lurk; animals that remain after their habitats are disrupted by agriculture and urbanization also tend to be those that host zoonotic diseases; and climate change has expanded the range of vector-borne diseases, like the Zika virus and Lyme disease. In short, pathogens are constantly on the lookout for greener pastures, and sometimes those pastures are created by us, bringing us closer to bats or the catlike civet. Then the pathogens themselves change, adapt, and sometimes truly thrive in the new landscape of our blood and lungs, far better real estate in which to reproduce and, yes, survive.

Many of the chapters in this book are about the origins of diseases, as these stories are the ones that ultimately teach us how to survive a novel, or not so novel, pathogen. In some cases, there is a clear so-called patient zero to a fresh outbreak, perhaps the most well-known of whom is Typhoid Mary Mallon (see ) who was wrongly singled out as the originator of the HIV outbreak in the United States.

A mosquito ( Anophelese stephensi ) captured in a colored image from a scanning electron microscope.

But the truth is we dont know the great majority of patient zeroes for a given disease, because the disease has been with us since time immemorial, or it erupted and spread too fast for us to pin down its origins, or other factors like politics or wars got in the way. Where possible, we present the person who can claim the dubious honor of being the first host to spread a disease, be it brand-new or very old but breaking out in a new population. In mining these beginnings, we reveal what investigators have always sought when researching disease: Why this person? How did they get it? How did that particular microbe evolve to cause such devastation? How can we stop it from happening again?