Three millennia ago, in perhaps the oldest permanent settlement on earth, a parasite may have changed the course of history.
For thousands of years, humans had been inhabiting the city of Jericho, also known as the City of Palms, where lush date palms and fig trees grew in a spring-fed oasis.
To Jericho’s south was the Dead Sea, where the Jordan River ended, its water too salty to use. And so, the inhabitants of Jericho depended upon a single water source—the clear, sweet, and abundant springwater.
And yet, within the precious springwater, scientists believe, lived Schistosoma hematobium, a deadly parasite. Traders had brought it to the oasis, and now the city’s inhabitants were all infected.
The consequences, the theory goes, were devastating. The women of Jericho had many miscarriages. Children bathed in the parasite-infested springwater often died in their teens. Adults were listless and weak. Some died from bladder cancer or heart disease; others suffered chronic debilitation. (Foundations of Parasitology, 6th Edition by Larry S. Roberts and John Janovy, Jr.)
Thus was the state of health of Jericho’s Canaanite population when the Hebrews, led by Joshua, prepared their attack on the city. Defenders suffering from chronic schistosomiasis would have been in no condition to maintain Jericho’s famous walls, much less engage in battle.
The Book of Joshua reports that a young woman named Rahab noticed two strangers in the street whom she guessed were Hebrew spies. She led them to her home and—in exchange for a promise to spare her family in the upcoming battle—likely informed them about the poor health of the city’s inhabitants. When a search party came knocking, she claimed the men had already left and later helped the spies slip away.
According to the biblical account, the Battle of Jericho then ensued. When it was over, not a Canaanite was left alive except Rahab and her family. Joshua then declared, “Cursed be the man before the Lord, that riseth up and buildeth this city of Jericho” (Joshua 6:26), and the dusty streets of Jericho were silent for hundreds of years thereafter.
Archaeological evidence indicates that despite the city’s attractiveness, Jericho remained a deserted ruin for some 400 years after the Hebrews passed through in their quest for the Promised Land. Within this period, without infected humans to maintain the cycle of contamination in the oasis, S. hematobium would have died out. Today, Jericho is once again inhabited, its oasis abundant and its waters parasite-free.
The Hebrew conquest of Jericho was in all likelihood no great military triumph, as trumpeted in the song lyrics, “Joshua fought the battle of Jericho… and the walls came tumbling down.” Because of S. hematobium, the defenders were probably not fit to fight. Nonetheless, we can credit Joshua for a very important achievement. His quarantine order restored this ancient oasis to a safe and beautiful habitat for future generations. One might even say that Joshua was the Bible’s first, albeit inadvertent, public health official.
Rosemary Drisdelle is a freelance writer with a professional background in medical laboratory science, particularly parasitology. This article was adapted from Parasites: Tales of Humanity's Most Unwelcome Guests, by Rosemary Drisdelle, published by the University of California Press. © 2010 by Rosemary Drisdelle.