Syphilis is a sexually transmitted infection (STI) that's caused by the Treponema pallidum bacterium. It's transmitted by direct contact with a sore called a chancre on an infected person.

The most common way to get syphilis is through vaginal, anal, or oral sex, but it's also possible to get it by kissing someone with a chancre on or around their lips or in their mouth, or by exposing an area of broken skin to a sore.

If left untreated, syphilis can have very serious long-term consequences. Fortunately, if caught in time, it can be treated with antibiotics, specifically penicillin.

The number of cases of both syphilis and congenital syphilis (syphilis passed from a mother to her baby) have been climbing in recent years. According to the Centers for Disease Control and Prevention (CDC), the number of babies born with syphilis in the U.S. is increasing at an alarming rate. 

"Testing for and treating syphilis during pregnancy more than 30 days before delivery can prevent this infection in newborns. Too many people are not being tested and treated early enough during pregnancy," the CDC said in a statement. 

The rates of syphilis are significantly higher in communities with high levels of poverty, low levels of education, and inadequate access to health care.

Syphilis in pregnancy can be very serious and cause miscarriage, stillbirth, and even infant death. That's why all pregnant women need to get tested for syphilis during their first prenatal appointment. It's also recommended that women who are high risk for syphilis be rescreened early in the third trimester and again at delivery.

A pregnant woman with syphilis can transmit the disease to her baby via the placenta, or if the baby comes in contact with a sore during a vaginal birth.

Syphilis progresses in stages, and symptoms differ from one stage to the next. People infected with the disease may not notice symptoms for years.

Primary stage

In the first stage, known as primary syphilis, one or multiple chancres on the vagina and genital area are the first signs of the infection. Sores can also develop in the anus and rectum and the inside of the mouth.

Chancres are usually painless and are round with raised edges, and they tend to show up about three weeks after exposure to the bacteria. Chancres typically take three to six weeks to heal, whether a person receives treatment or not.

If they don't receive treatment, the bacteria (known as spirochetes) are likely to continue to multiply and spread throughout the bloodstream. When this happens, the disease progresses to the secondary stage.

Secondary stage

In the secondary stage, syphilis can have a variety of symptoms that appear in the weeks or months after the chancre has healed. But again, symptoms might not be noticeable.

At this stage, symptoms may include:

• A non-itchy syphilis rash on one or more parts of the body, such as the torso, the palms of the hands, and the soles of the feet. The syphilis rash usually appears as rough, red or reddish-brown spots.

• Large grey or white lesions (condyloma lata) in the mouth, underarm, and genital area.

• Hair loss

• Muscle aches

• Fever

• Sore throat

• Swollen lymph nodes

Syphilis symptoms are recurrent – they can disappear for periods of time and then return.

Symptoms may go away with or without treatment, so it's important to get tested if you think you've been exposed or are at high risk. If you don't seek treatment, the infection will stay in your body. You may not have any syphilis symptoms for years, or you could develop tertiary syphilis.

Tertiary syphilis

About 15 to 30 percent of people who don't get proper treatment will develop what's called tertiary syphilis.

This late stage of the disease can develop up to 30 years after a person was infected, and can cause serious health issues. Large sores called gummata can develop on the skin and in a host of organs, including the heart, brain, eyes, and liver. It can also affect the bones and joints. Fortunately, most people get treated early enough and very few develop tertiary syphilis.

Yes, it can. Syphilis can travel from the bloodstream across the placenta and infect a baby anytime during pregnancy. The infection can also happen if a baby comes in contact with a chancre during vaginal delivery. The risk of fetal infection is highest during the primary and secondary stages of the disease.

Syphilis in pregnancy raises the risk of miscarriage, premature birth, fetal growth restriction (low birth weight), and issues with the placenta and umbilical cord. For example, the infection may cause the placenta to grow overly large and the umbilical cord to be swollen.

Babies who become infected may develop symptoms a few weeks or months after birth. These symptoms include:

• Fever

• Inability to gain weight

• Cracking of skin at the mouth, genitals, and anus

• Rash on the palms and soles

• Watery fluid from the nose

An estimated 40 percent of babies born to pregnant women with an untreated infection will be stillborn or die after birth.

If the disease isn't treated, babies with congenital syphilis can develop long-term health issues. That's why it's critical for women to be tested and treated during pregnancy, and for any baby who may have syphilis at birth to be fully evaluated and treated as well.

Penicillin is the only antibiotic that's both safe to take during pregnancy and able to successfully treat both a mother and baby for syphilis.

If you have primary, secondary, or early-stage syphilis, you'll receive a single dose. Adults in the later stage of the disease will have three doses in weekly intervals. If you're allergic to penicillin, you'll need to be desensitized to the drug before you take it.

Treatment for syphilis in the second half of pregnancy can cause a reaction in some women called the Jarisch-Herxheimer reaction. This can cause symptoms of preterm labor and abnormalities in the baby's heart rate. (If you notice any contractions or a decrease in fetal movement, call your provider immediately. In some cases, your provider may opt to treat you in the hospital so you can be monitored.)

Your partner will also need to be tested. They'll be treated if the test results are positive or if you've had sexual contact in the last three months, even if their blood test result is negative. You'll need to refrain from sexual contact until both of you have been treated. After syphilis treatment, you'll have regular blood tests to make sure the infection has cleared and you haven't been reinfected. You'll have an ultrasound to check on your baby.

The CDC recommends that all pregnant women be screened for the infection at their first prenatal visit. All but four states have laws requiring syphilis testing during pregnancy, and some states require retesting during delivery.

Some pregnant women are advised to be retested for syphilis during their third trimester, including:  —

• Those who live in communities where the rates of infection are high

• Those who weren't tested at their first prenatal appointment

• Those who had a previous positive result

• Those at a high risk due to multiple sex partners and drug use 

• Those who contracted another STI during pregnancy

• Those who develop symptoms of syphilis (or have a partner with symptoms)

Testing for syphilis is a two-step process: Your healthcare provider can walk you through it.

Having syphilis makes you more susceptible to HIV if you're exposed to it, so if you test positive for syphilis, you'll need to be tested (or retested) for HIV and other STIs. And if you have primary syphilis, you'll need to be tested for HIV again in three months.

To protect yourself from syphilis, have sex with only one partner, and make sure that person has tested negative for syphilis. Male condoms can prevent transmission of HIV and other STIs, but they only offer protection from syphilis if the sore is on your partner's penis – they won't protect you from sores that aren't covered by the condom.

Remember, too, that you can get syphilis if a partner's sore touches any of your mucous membranes (such as in your mouth or vagina) or broken skin (a cut or scrape).

If you've had syphilis once, that doesn't mean you can't get it again. You can become reinfected.

If there's a possibility that you've been exposed to syphilis or any other STI during pregnancy, or if you or your partner has any symptoms, tell your provider right away so you can be tested and treated if necessary.