Syphilis, a classic sexually transmitted disease nearly eradicated decades ago, is seeing a resurgence in Japan, with the reported number of patients in 2017 topping 5,000 for the first time in 44 years.

According to the National Institute of Infectious Diseases, the number of people diagnosed with syphilis rocketed to 5,770 in 2017, more than double the 2,697 seen in 2015 and far exceeding the 621 in 2010.

In November 2016 the Health, Labor and Welfare Ministry launched a PR battle against sexually transmitted diseases including syphilis, tapping Sailor Moon — a female fighter from the eponymously titled popular manga/anime series — as its advocate and printing leaflets of the character quipping, “I will punish you if you don’t get tested!!”

But such calls to arms have failed to stop the rapid rise of the disease, whose early symptoms can be easily ignored and which, if untreated, can cause serious complications.

Today we examine syphilis in more detail:

What is syphilis and what does it do to your body?

Syphilis is a sexually transmitted infection caused by a bacterium called treponema pallidum. The Japanese name baidoku, written with the kanji meaning “plum” and “poison,” comes from the way patients develop a red skin rash that looks like red bayberries, according to the health ministry.

People can become infected through direct contact with a syphilis sore during vaginal, anal or oral sex. Syphilis can also spread from an infected mother to her fetus.

Syphilis is divided into primary, secondary, latent and tertiary stages. Different signs and symptoms appear with each stage, but early signs are easily missed.

According to the ministry, patients with primary syphilis develop firm sores at the original site of infection — usually on or around the genitals, around the anus or in the rectum, or in or around the mouth. But the symptoms at this stage cause no pain and recede after a while. It’s best for people to get tested early because the infection remains even after the sores are gone, and those who have been infected may still spread the disease to others. The secondary syphilis stage appears around three months later. By then infection has spread throughout the body and patients develop skin rashes, often on the palms of the hands and the soles of the feet. But symptoms can disappear within weeks naturally. The condition can be ignored or can be mistaken for symptoms of allergies, rubella or measles.

Dr. Kunio Kitamura, chairperson of the Japan Family Planning Association, said many patients visit hospitals when they develop a skin rash. But because the rash can disappear even if untreated, some people ignore the rash and forgo treatment at this point. The latent and tertiary syphilis stages appear several years later, when patients can develop rubber-like tumors across the body, on the skin, in the muscles or within bones. Patients also suffer damage in their internal organs, including the heart, blood vessels and the brain, which can ultimately result in death. Kitamura added, however, that most patients are treated by then so late-stage syphilis cases are rare nowadays.

Can it be treated?

Yes. Syphilis can be treated with the antibiotic penicillin, experts say, adding that the dosage and period over which the drug should be taken varies from stage to stage.

But treatment might not undo damage the infection has already done. Condoms are effective to reduce the risk of infection, though they won’t work if infected sites are outside areas that are covered by the condoms. Kitamura said patients in Japan must take penicillin pills for several weeks because the government has not approved the use of penicillin injections — which, with just one shot, can cure syphilis.

Why are the number of infections increasing?

The exact causes are unknown and are being studied by doctors and researchers.

Kitamura said doctors have recently become more aware of the illness thanks to a recent government campaign and greater media coverage, which has led to more tests and more reports of infections. Doctors are mandated to report all syphilis cases to prefectural governments within seven days.

Kitamura noted that unlike other developed countries where men who have sex with men have been associated with the rise, the increase in Japan has been attributed more to heterosexual encounters. Women who have one-off sexual encounters with men they become acquainted with through social media are also at high risk, he said.

Dr. Makoto Ohnishi, director of the department of bacteriology I at the NIID, is leading a ministry-commissioned study on syphilis cases in Tokyo. Ohnishi said syphilis is far more infectious than HIV/AIDS, with an infection rate of 10 to 50 percent. He suspects that given the recent surge in the number of women with the disease, women engaged in sex work are among the high-risk groups.

To understand how high-risk people contract the disease, Ohnishi’s group, with the help of clinics in Tokyo, is studying nearly 400 women — mostly sex workers — who get tested for syphilis, with the aim of comparing patterns of behavior between those who become infected and those who don’t. Tokyo is the epicenter of the syphilis outbreak, with roughly 30 percent of all cases — far higher than other cities.

Is there any truth to comments attributing the rise in syphilis cases to tourists from overseas?

In December, Nobuyuki Suzuki, a male assembly member for Tokyo’s Katsushika Ward, caused uproar by tweeting that the recent upsurge in syphilis cases is due to more tourists from abroad — especially from mainland China — bringing the bacterium into the country and spreading the disease by visiting sex industry establishments.

Ohnishi said that infection routes are impossible to nail down and that such arguments are based on the mere fact that the timing of the increase in syphilis cases coincides with a surge in tourist numbers. “I won’t even take such claims seriously,” he said. But it’s important to understand, he added, that for anyone who uses the nation’s heterosexual sex industry, the risk of syphilis is there. This is unlike the United States, for example, where the risk of infection through using heterosexual sex services is low.

Where can people get tested for syphilis?

Urology, gynecology and dermatology clinics can perform a blood test for syphilis. Many municipal public health centers also offer anonymous screenings for free. You can also find information in English and Japanese about HIV/AIDS consultation centers that also offer syphilis tests at www.hivkensa.com .