What Is Chancroid?

Chancroid is a highly contagious sexually transmitted infection (STI) that causes genital ulcers. Although it is rarely seen in the United States, chancroid is relatively common in certain parts of the developing world. As with syphilis, the open sores caused by chancroid increase a person's risk of getting other STIs, including HIV.

This article looks at the symptoms and causes of chancroid, including how it differs from syphilis. It also explains how chancroid is diagnosed and treated and what you can do to protect yourself and others from infection.

Chancroid Symptoms

Chancroid is often mistaken for syphilis in the early stages. It usually starts as a red bump on the genitals or rectum that quickly turns into a pus-filled blister, usually within four to 10 days of exposure. The blister will typically rupture and form a deep ulcer with well-defined borders.

Unlike syphilis, the ulcers usually grow to a larger size—some as large as two inches—and can be extremely painful. By contrast, syphilis ulcers, called chancres, are usually painless. The base on a chancroid ulcer can bleed easily if scratched or rubbed.

Chancroid can also cause swelling, tenderness, and inflammation of the lymph nodes in the groin. In fact, the swelling can sometimes be so severe that the lymph node rupture, causing a draining abscess. This is also not a symptom associated with syphilis.

Males with chancroid generally get one ulcer, while females can get many. Females may also experience dysuria (pain with urination), while males usually won't.

Untreated chancroid ulcers can persist for up to three months and cause significant scarring.

Cause

Chancroid is caused by the bacteria called Haemophilus ducreyi. The infection is highly contagious and easily passed during sex by direct contact with fluids from the open sores.

The bacteria can also pass through tiny breaks in the skin, called microabrasions, that occur during sexual intercourse.

Additionally, a person can spread the infection from the genitals to other parts of their own body by touching a sore and then touching their eye or other areas of skin. This is referred to as autoinoculation.

Chancroid is relatively rare in the United States, although sporadic local outbreaks have been known to occur. Worldwide, chancroid is the most common cause of genital ulcer disease, particularly in resource-poor parts of Africa and the Caribbean.

Chancroid can increase the risk of HIV by allowing the virus easier access to the body and increasing the number of antibodies, called CD4 T cells, that HIV targets for infection. These factors contribute in part to the high rate of HIV transmission in developing countries where both chancroid and HIV are widespread.

Diagnosis

No laboratory test is able to immediately confirm the diagnosis of chancroid.  There are also no FDA-cleared tests available to accurately detect Haemophilus ducreyi.

Although special tests are available to culture (grow) Haemophilus ducreyi in the lab (using a swab of fluid from a sore), they are difficult to source and are less than 80% accurate. Some labs in the United States have developed their own tests, called nucleic acid amplification tests (NAATs), to help diagnose chancroid.

But, for the most part, chancroid is diagnosed based on the features of the disease and the exclusion of other diseases that cause genital ulcers.

Treatment

As a bacterial infection, chancroid is treated with antibiotics. There are four treatment regimens recommended by the CDC that are given either orally (by mouth) or intramuscularly (by injection into a large muscle). Each dose is measured in either grams (g) or milligrams (mg).

For reasons not entirely clear, uncircumcised males and people with HIV are sometimes less responsive to treatment and may need to be re-treated. For this reason, follow-up testing should be performed three to seven days after completing therapy. For most people, symptoms will start to improve within that time frame.

Anyone suspected of having chancroid should also be tested for HIV.

Prevention

Chancroid is prevented in the same way as many other STIs, with barrier protection and other safer sex practices. Short of abstinence, this includes:

• Using condoms consistently and correctly, including external (male) and internal (female) condoms
• Always use condoms during vaginal and anal sex
• Using a condom for oral sex on a penis
• Using a dental dam (or a condom cut in half lengthwise) for oral sex on a vagina or anus
• Limiting your number of sex partners

You should also notify sexual partners immediately if you have been diagnosed with chancroid. Sexual partners will likely be treated as a precaution.

Summary

Chancroid is a rare sexually transmitted infection caused by the bacteria Haemophilus ducreyi. Chancroid looks similar to syphilis but causes larger genital sores that are painful. Around half of the people with chancroid will experience swollen lymph nodes in the groin.

Chancroid can be spread by coming into contact with fluid from an open sore during vaginal, anal, or oral sex. There are no tests licensed for the diagnosis of chancroid; as a result, the diagnosis is often made based on symptoms and the exclusion of all other likely causes.

Chancroid is treated with either or injected antibiotics. Follow-up testing is recommended to ensure the infection is fully cleared.

A Word From Verywell

Because chancroid closely resembles syphilis, it is important to give your health provider your complete medical and sexual history so they can reach the correct diagnosis. This includes advising the provider if you've had sex with a recent immigrant or visitor from parts of the world where chancroid is widespread.

The differentiation is especially important because chancroid and syphilis are treated differently. What works for syphilis will likely not work for chancroid, and vice versa.