A new report from the Department of Defense (DoD) found that syphilis is on the rise among active military service members. There has been a 41 percent rise in the rate of the sexually transmitted infection (STI) since 2010.

The report notes that syphilis trends among service members mimic those of the general public, but suggests the military should create targeted prevention campaigns.

Syphilis is one of the oldest known STIs, with recorded cases dating back to the 1400s. It is a bacterial infection that causes small, round, painless sores to appear on the genitals, anus, lips, or inside the mouth. The infection is spread through contact with these sores. If caught early—in what is known as the primary stage—the disease can be easily cured with antibiotics.

If left untreated, it can proceed to the secondary stage, which can cause a rash to appear all over the body as well as a host of other symptoms, including lesions on mucous membranes, fever, swollen lymph glands, sore throat, patchy hair loss, headaches, weight loss, muscle aches, and fatigue.

Though these symptoms may be severe, they are often attributed to other illnesses, and syphilis then proceeds to the latent stage, which can last as long as 20 years. During this time, a person may have no visible symptoms, but the disease can be damaging to the brain, nerves, eyes, heart, blood vessels, liver, bones, and joints.

The Centers for Disease Control and Prevention (CDC) in 1999 undertook a syphilis elimination campaign because rates of the disease were so low (6,657 cases of primary and secondary syphilis). Public health experts believed they could wipe it out completely. That didn’t happen. Instead, the disease has made a resurgence over the past decade.

In 2013, the syphilis rate was 5.3 cases per 100,000 people, which was more than double the lowest-ever rate, 2.1 per 100,000, in 2000. The majority of cases that year—75 percent—were among men who have sex with men.

The new report suggests the military is seeing similar trends. The rate of syphilis among active service members rose 50 percent between January 2010 and August 2015—from 31 per 100,000 members to 47 per 100,000. In total, there were 2,976 individuals diagnosed. Most cases were diagnosed in the early stages, but 244 cases were considered advanced. The majority of the cases (92 percent) were males.

Nearly one in four service members diagnosed with syphilis were also HIV-positive.

Despite the increase in syphilis in the military, it remains one of the less common STIs among service members. Like in the general public, human papillomavirus (HPV), chlamydia, gonorrhea, and herpes are more common than syphilis in the military.

One difference between the general population and the military population is the groups that are most affected. In the general population, Hispanic and white men have the highest rates of syphilis, but in the military, Black men are the hardest hit.

The authors of the DoD report say that they cannot be sure why syphilis is on the rise, but theorize that the military is seeing trends similar to those in the general public—such an increase in individuals having unprotected intercourse, meeting partners on the Internet, and choosing activities like oral sex, which according to the report “can decrease the risk of HIV transmission but conversely increase the risk of contracting syphilis.”

The report authors suggest that the military develop and implement syphilis prevention measures that target those service members most at risk. They say it should continue an aggressive partner notification program, which can prevent the spread of disease by getting the partners of those infected tested and treated before they have the chance to spread the disease further.