Rat urine. As we feast on succulent turkey, moist stuffing, and glistening cranberry sauce this Thanksgiving, the furthest thing from our minds is probably rat urine.
Yet it’s quite possible that America as we know it would not exist without rat urine and leptospirosis, the disease it spreads. The disease conveniently cleared coastal New England of Native Americans just prior to the Pilgrims’ arrival and later killed the helpful Squanto. It still lurks among us, underdiagnosed, an emerging menace.
In the winter of 1620, the Mayflower happened to dock at an abandoned village. It had been known in the local Wampanoag language as Patuxet. Pilgrims rejoiced; the land “hath been planted with corn three or four years ago, and there is a very sweet brook runs under the hillside.” In fact, the French explorer Samuel de Champlain had observed what would become Plymouth harbor 15 years earlier and drew a map of native homes surrounded by fields of corn.
Where had all the people gone? As the Pilgrims thanked God for their luck, they were unaware that the previous tenants had died of a gruesome infectious disease.
In the spring of 1621, the Pilgrims finally met their surviving neighbors. If the colonists thought God was good for guiding them to pretilled land and a sweet brook, they were even more thankful when the first Native American strolled into their midst, smiling and saying in English, “Welcome!” According to Pilgrim-era writings, he told them straight away that the previous villagers “died of an extraordinary plague.” A few days later, Tisquantum arrived. Called Squanto by Pilgrims, he was born in Patuxet, abducted by Englishman Thomas Hunt in 1614, and missed out on the epidemic that killed his entire village. During his years in captivity, he’d learned English, and he was now attached to a nearby branch of the Wampanoag.
The Pilgrim leader William Bradford was already aware of the death toll from “Indean fever.” His scouts had ventured inland and noted “sculs and bones were found in many places lying still above ground, where their houses and dwellings had been; a very sad spectackle to behould.” It’s estimated as many as nine out of 10 coastal Indians were killed in the epidemic between 1616 and 1619.
What killed so many people so quickly? The symptoms were a yellowing of the skin, pain and cramping, and profuse bleeding, especially from the nose. A recent analysis concludes the culprit was a disease called leptospirosis, caused by leptospira bacteria. Spread by rat urine.
Leptospirosis is what’s known as a zoonotic disease. The bacterium lives in animal hosts and is transmitted between animals and to people via urine in fresh water. Its favorite host is the black rat, Rattus rattus (the rat so nice they named it twice), a nonnative species that was inadvertently transported to North America on explorers’ ships. For unknown reasons, it’s the only animal whose kidney can sustain continuous leptospira infections. The tubules of an infected rat’s kidney are lousy with bacteria and excrete hundreds of thousands in every drop of urine (10 million leptospira per milliliter, according to one study). Meanwhile, just 10 bacteria, injected into the abdomen, will send a laboratory hamster to violently hemorrhagic death within days. Leptospira is in a family of spiral-shaped bacteria called spirochetes, along with the bugs that cause syphilis and Lyme disease.
Leptospira is shaped like a thin corkscrew, but at corkscrew width it’d be more than 4 feet long. Under the microscope, the bacteria look like delicate ramen or living handlebar mustaches. Holding one end rigid like a rudder, they spin the other like a motor to move. They are single cells with no brain, per se, but they quest about sniffing out food, such as blood. The more virulent the strain, the more the bacteria are drawn to blood cells. They metabolize iron to survive and secrete an enzyme enabling them to smash open a red blood cell and slurp up the sweet, sweet iron within.
Leptospira swim faster in higher viscosity; they are built to tunnel through organs and cell membranes in order to evade the immune system. With their unique shape and motility, they can pass straight through a cell, like a corkscrew through a candied sweet potato. If immune cells are able to catch and smash one, that is when the trouble starts. A robust immune response can actually be detrimental because the more leptospira get blown to smithereens, the more bacteria bits are floating about to activate the immune system. This may be one reason why leptospirosis is most fatal to otherwise healthy men.
Like Pilgrims in the New World, leptospira must first penetrate the host. Invisible in water, the bacterium enters the eyes, the nose, or scrapes in the skin. Then it disseminates, looking to colonize the kidney. Humans are a dead end; our kidneys aren’t the right environment for them to set up and multiply. Like colonies at Jamestown, Roanoke, and Popham, the bacteria get ambushed or die of starvation, and the infection is usually cleared within a month if it isn’t fatal.
According to the hypothesis, infected ship rats landed in the New World and excreted leptospira, infecting raccoons, mink, and muskrats whose urine further contaminated any standing fresh water. It is unclear why this particular infectious disease should afflict Native Americans and not subsequent European colonists. Prior exposure does not necessarily result in immunity because there are a number of different infectious strains.
A clue might lie in the way these different cultures interacted with natural environments. The Wampanoag gathered sharp-edged clams, skinned pelts from beaver and deer, canoed through streams, and were much fonder of bathing than were Europeans of that era. And they likely spent time hand-picking wild cranberries from bogs on Cape Cod. Wampanoag have long had seasonal feasts of thanksgiving, one of which celebrates the cranberry harvest. There is some evidence that cranberries were also used medicinally—raw, ground into a poultice, and applied to open wounds. Although modern research suggests that cranberries can be a potent antimicrobial, that might not have been enough to slay the spirochete. The more leptospira that initially invade the bloodstream (possibly via direct contact with berries), the more likely the disease is to be fatal.