Haemophilus ducreyi arrange themselves in parallel rows, which researchers have called “railroad tracks,” “schools of fish,” and “fingerprints.” Image: Mike Miller, CDC
Earlier this year, I asked a room full of scientists and medical professionals to raise their hands if they’d ever heard of chancroid. Everyone sat there, motionless, confused by the odd syllables I had uttered — shan kroyd. If you’ve never heard of chancroid, you’re not alone.
Chancroid is a sexually transmitted disease (STD) brought to you by Haemophilus ducreyi, a type of bacteria that can pass through microscopic tears in the skin during sexual contact. When one partner is infected, there is a 1 in 3 chance the other will become infected. An infection can cause painful sores and swollen lymph nodes, most often in the genital region. About half of people with chancroid infections will experience “buboes,” or swollen lymph glands that might rupture. Before it could be cured with antibiotics, a persistent infection could cause permanent skin damage.
Humanity can make chancroid the first STD to go extinct.
One reason you probably haven’t heard of chancroid is that, in the developed world at least, it has mostly disappeared. In fact, researchers believe chancroid can be completely wiped off the planet — which would make it the first STD ever to be forced into extinction. How amazing would that be?
Chancroid has been hopping from loin to loin since at least the days of the ancient Greeks, and was common until the 20th century, when rates began to decline. Thanks to antibiotics, U.S. chancroid rates decreased 80-fold between 1947 and 1997, all but vanishing by the late 1950s. It was virtually unheard of until there was another spike in the 1980s, correlating with the crack epidemic. But, since 1987, cases have been steadily declining.
Reported chancroid cases by year, United States, 1941–2015
Since 2000, chancroid rates in the United States have been so low that they round down to zero — as in, zero cases of chancroid per 100,000 people, the metric used to report most STD rates. In 2015, only 11 cases of chancroid were reported in the entire country. Planned Parenthood no longer lists chancroid on their website (though it was there as recently as May 2017), and the CDC relegates it to the bottom of their STD webpage, under “Other STDs.”
Why is chancroid a dusty memory, while other STDs like gonorrhea and syphilis never went away?
According to the World Health Organization, a couple of factors transformed chancroid from one of the most common STDs in the world to one most people haven’t heard of. First, antibiotics made chancroid curable. Second, increased economic opportunities for women led to lower rates of prostitution, and remaining sex workers moved out of brothels and consequently had a reduction in sexual partners.
But it wasn’t just medical advances and shifts in sex work that drove chancroid rates into the ground. If it were as simple as that, we would have vanquished other bacterial STDs as well. H. ducreyi, the bacteria that cause chancroid, isn’t as hardy as those that cause more common STDs like gonorrhea or chlamydia — it has a short window of infectiousness (about 45 days), so the disease can only be sustained in populations of people who have high numbers of sex partners (defined by WHO as 15-20 partners per year) — especially populations in which condom use is uncommon and sexual activity is continued even in the presence of symptoms.
It’s also important to note that most people with chancroid have awful symptoms. That might sound like terrible news, but one reason chlamydia is so common is most people with the infection don’t have symptoms and can transmit it to others unknowingly. Chancroid, on the other hand, is usually so unpleasant that people are motivated to seek treatment, decreasing the period during which they can pass it to their partners. Thanks to health-care access, the occasional outbreaks that pop up in the United States are quickly stamped out.
Chancroid, however, never actually went away — it’s still endemic in regions with poor health-care infrastructure, including parts of Africa, Asia, and Latin America. Also, because H. ducreyi is difficult to culture, it could be underdiagnosed. It wasn’t until the 1970s that we found good ways to study the bacteria in the lab, but even to this day diagnosis is difficult.
Getting solid numbers on this slippery organism is tricky, but annual chancroid cases worldwide are in the ballpark of 6 million. Chancroid is most common in countries with high HIV prevalence — bad news, given that chancroid amplifies HIV transmission. Chancroid is the most common cause of genital ulcers in developing countries with serious HIV epidemics, and some estimates hold that genital ulcers increase HIV risk by a factor of as much as 300 for each act of unprotected vaginal sex. Ulcerative STDs like chancroid (as well as herpes and syphilis, which are often confused for chancroid) greatly increase HIV risk, as viruses use ulcers as portals for transmission.
The conditions that allowed chancroid to flourish in 19th and 20th century Europe and North America were similar to those that enable high chancroid prevalence in many developing countries today — expanding urban centers attract male workers, driving a demand for prostitution, especially when economic opportunities for women are scarce. But, because chancroid has been nearly erased in the developed world, there is hope it can be defeated elsewhere — and, over the past couple of decades, many developing countries have conquered chancroid, for example by promoting condom use and STD treatment to sex workers. Additionally, worldwide efforts to control HIV have the wonderful side effect of reducing chancroid.
The bacteria’s weaknesses plus humanity’s strengths combine to make chancroid a prime candidate for eradication — that is, we can completely wipe it off the planet. The bacteria have difficulty sustaining themselves in a population without high turnover of sex partners — and even in that case, they’re no match for antibiotics. Social changes, such as promoting economic opportunities for women and expanding health-care access, can help us pound the last nails in chancroid’s coffin.
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