“In the yere of Chryst 1493 or there aboute this most foule and most grievous disease beganne to sprede amonge the people,” a German scholar named Ulrich von Hutten wrote soon after the first known outbreak of syphilis swept across Europe.

In his book Guns, Germs, and Steel, the historian Jared Diamond elaborated: “Its pustules often covered the body from the head to the knees, caused flesh to fall off people’s faces, and led to death within a few months.”

Today, syphilis can seem like a historical relic, more likely to appear in period movies than in one’s next-door neighbor. But after more than a decade of increases in syphilis cases, the United States is looking at its highest rate in recent memory.

According to a report released on November 17 by the Centers for Disease Control and Prevention, syphilis rates rose for both genders in every region of the U.S. in 2014. The rate of reported primary and secondary syphilis (the earliest symptomatic stages of the disease) increased by 15.1 percent from 2013 to 2014, to 6.3 cases per 100,000 people. The rate of reported congenital syphilis (passed by an infected mother to her child during pregnancy) increased by 27.5 percent, to 11.6 cases per 100,000 live births.

Syphilis had become relatively rare in developed countries since the discovery of penicillin, though it continues to plague many parts of the global South. At the turn of the millennium, it looked as though the United States had all but eliminated the disease. After an outbreak in the early 1990s, diagnoses of primary and secondary syphilis had dropped to 2.1 cases per 100,000 people—the lowest rate since the U.S. began recording it in 1941. But in 2002, the downward trend began to reverse.

The new wave of syphilis shows no signs of slowing down. In New Orleans, the number of syphilis cases tripled between 2012 and 2014. Central New York, which two years ago reported 27 syphilis cases, most recently reported 110, and some health clinics are now offering free syphilis testing. Health officials in Oregon, where syphilis rates have increased by more than 1,000 percent from 2007 to 2014, have created a new website, syphaware.org. The site's homepage reads, “Oregon is known for many things: natural beauty, coffee, beer, and Pinot Noir. Did you know that Oregon is also known for syphilis?”

Researchers are still trying to work out why these increases are happening now, but the CDC’s report offers a few clues. For one, syphilis isn’t the only sexually transmitted disease becoming more common. Syphilis, chlamydia, and gonorrhea—the three STDs that comprised the focus of the report—rose simultaneously for the first time on record, which suggests an underlying cause that isn’t syphilis-specific.

Some health officials point to the growing role of technology in people’s sex lives, specifically apps like Tinder and Grindr that facilitate casual sex between partners who don’t know each other’s sexual histories. But there’s no conclusive evidence that these apps have played a role in syphilis outbreaks, especially given that Tinder was released more than a decade after syphilis rates began rising again in 2002.

Sarah Kidd, an epidemiologist at the CDC, believes dating apps can pose a diagnostic problem, since controlling the spread of syphilis relies on being able to notify an infected person’s sexual partners.“We do know that with the rise of so many apps, it's easier to meet partners and not necessarily have identifying information and not be able to track them down later,” she says.

Compared to chlamydia and gonorrhea, syphilis is particularly challenging from a public-health perspective because most Americans don’t think of it as a threat. The worst epidemics happened centuries ago, when the infection had no known cause or cure. In the early 16th century, the Italian physician Alexander Benedictus suggested that syphilis was spread through “a venereal taint produced in the sexual organs of women by the alteration of humors which they exhale.”

A poster from Britain’s wartime
campaign against venereal
disease in 1943-1944 (Wikimedia)

Across the world, people also blamed foreigners for bringing syphilis into their countries. In his book Opus Ultimum, Daniel N. Leeson writes: “The English called syphilis ‘The French Disease’; the French called it ‘The Italian Disease’; the Italians called it ‘The Turkish Disease’; the Russians called it ‘The Polish Disease’; and both the Japanese and the Indians termed it ‘The Portuguese Disease.’ Only the Spanish accepted any blame, referring to it as ‘The Spanish Disease.’” (They may have had good reason. Some historians believe that Columbus and his crew brought the infection from America upon returning to Europe, though that theory was challenged just last week when researchers found signs of congenital syphilis in the skeleton of a European child who died in the 14th century.)

Syphilis has afflicted some of the West’s most famous cultural icons. Vincent Van Gogh, Franz Schubert, and Robert Schumann had it; so did Charles Baudelaire, Gustave Flaubert, Oscar Wilde, and Friedrich Nietzsche. Ludwig van Beethoven, Wolfgang Mozart, and James Joyce all had symptoms of what may have been syphilis, according to some researchers. Al Capone had the mental capacity of a 12-year-old child when he died at 48, the result of dementia from neurosyphilis. Shakespeare’s plays and poetry are littered with allusions to syphilis: “the pox,” “the infinite malady,” “the malady of France,” “the incurable bone-ache.” In 1520, the humanist scholar Desiderius Erasmus declared it “the most destructive of all diseases … What contagion does thus invade the whole body, so much resist medical art, becomes inoculated so readily, and so cruelly tortures the patient?”

The version of syphilis that Shakespeare and Erasmus knew was brutally efficient, often causing death within a few months. Later strains of the infection progressed in a more gradual series of stages. Syphilis is most recognizable during the primary stage, when a painless sore marks the location where the infection entered the body. It can take up to 90 days after infection for the sore to appear, usually on or inside a person's genitals or mouth. The secondary stage is marked by a skin rash and sometimes other symptoms, including fever, headache, sore throat, swollen lymph glands, weight and hair loss, and fatigue. All of these symptoms disappear when syphilis enters its latent stage, but the infection remains in the body. In 15 percent of untreated syphilis cases, the disease resurfaces 10 to 20 years after the first infection, causing brain and muscle damage, paralysis, blindness, and even death.

Syphilis is not the mysterious disease it once was. We know that it spreads when someone else comes in contact with the sore, most often during penetrative or oral sex. And we know that syphilis is completely curable with penicillin, though penicillin won’t erase any damage the infection has already caused. The problem is identifying it in the first place—the symptoms of syphilis often mimic those of other diseases (which explains why, over a century ago, syphilis earned the nickname “the great imitator”). It’s entirely possible to go through the early stages of the infection without knowing it.

Some populations are especially at risk. Unlike the mainly heterosexual outbreak in the early 1990s, the majority of syphilis cases in 2014 appeared in men who have sex with men (though syphilis rates also rose among women by 22.7 percent). Kidd suggests that people might be less careful now that the threat of HIV/AIDS is less immediate than it was in the 1990s, or that partners might use strategies to prevent HIV transmission that aren’t as effective for other STDs. Condoms, for instance, are a good precaution but not a reliable prevention method for syphilis, as the infectious sore might be on an area that remains uncovered.

Because syphilis can be difficult to prevent and to recognize, the CDC is encouraging sexually active people, especially pregnant women and men who have sex with men, to get regular syphilis tests. Health officials also stress the importance of raising public awareness—“A big [issue] is knowing that the disease still exists,” says Kidd—but raising awareness quickly becomes a policy issue. Budget cuts have made it harder for clinics to do outreach and offer free STD tests. Sex education in schools remains limited and sometimes nonexistent.

In Saline County, Kansas, 12 new cases of syphilis have been confirmed since August. Jason Tiller, the coordinator of Saline’s health department, believes yet another challenge is that physicians as well as patients aren't used to considering syphilis as an option. He brings up a common saying in medical school: “When you hear hoofbeats, think horses, not zebras”—a reminder that the most likely diagnosis is often correct. If someone walks into a clinic with a rash, in other words, it's probably something like poison ivy. Unless, as is increasingly the case, it’s secondary-stage syphilis. Sometimes the hoofbeats are zebras.