STD Awareness: 10 Sexually Transmitted Diseases You Probably Don’t Know About

Giardia lamblia, a microbe that can be transmitted sexually. Image: NIH

Gonorrhea and chlamydia go back to antiquity. Syphilis took hold in Europe during the late 15th century. Herpes wasn’t on most people’s radars until the early 1980s, and human papillomavirus (HPV) was relegated to relative obscurity in the popular imagination until the HPV vaccines made their debuts less than a decade ago.


Have you heard of CMV, chancroid, or donovanosis?


But there are still a handful of sexually transmitted diseases (STDs) that you might not know about. These include incredibly common infections, as well as those caused by pathogens you might have heard of but probably don’t associate with sexual transmission. They also include infections that are very rare here in Arizona but are much more common in other parts of the world. They all deserve a closer look.

10 Trichomoniasis: What is the most common curable STD? You might guess that it’s chlamydia or gonorrhea, but according to the Centers for Disease Control and Prevention, it’s trichomoniasis (also known as trich, pronounced “trick”). This infection is caused by Trichomonas vaginalis, a single-celled parasite that is actually pretty cute as far as microbes go. What’s not so cute is its propensity to attach to your cells and degrade their surfaces, which on a large scale can produce unpleasant symptoms. While not everyone has symptoms, they can include vaginal or penile discharge, itching or swelling in the vaginal area, an increased urge to urinate, and pain during urination. Trich is spread by vaginal or anal intercourse, direct vulva-to-vulva contact, and other activities that involve passing secretions from one partner to another. Learn more about trichomoniasis on our blog.

9 Infectious mononucleosis: Epstein-Barr virus (EBV) causes infectious mononucleosis (also known as mono). Merely being in the presence of someone with mono won’t put you at risk — you need to be actively swapping spit with them to be exposed to the virus; hence mono is often called the “kissing disease.” (Sharing cups or eating utensils can do it, too.) Luckily, the majority of us are infected as children, when the virus is usually harmless. If we’re not exposed until adolescence or adulthood, however, we can develop mono, which can present with fever and cold-like symptoms. Mono is no fun: As one adult sufferer of mono described it, “I was too exhausted to stand up for the duration of a shower, and simple tasks like making toast or washing a single dish proved ridiculously challenging.”

EBV can also show up in the genital tract — in vaginal, cervical, and penile secretions, as well as on the head of the penis. Researchers say it is highly probable that EBV can be transmitted sexually as well as by kissing — but most sexual partners are probably also kissing each other, so teasing both modes of transmission apart might be difficult.

EBV is a member of the herpesvirus family, along with the viruses that cause herpes and chickenpox. Like all herpesviruses, once we are infected with it, the virus remains dormant in our bodies for the rest of our lives. This means that asymptomatic individuals can act as “reservoirs” for the virus and unknowingly infect others. Luckily, previous infection usually means you’re not at risk for developing mono. More information about EBV can be found at the CDC’s website.

8 Parasitic infections: Intestinal parasites are usually transmitted by fecal contamination of food or water, which can be tainted by billions of infectious particles. Some pathogens, however, are easier to transmit sexually because it only takes a few infectious particles to make you sick. Oral or manual contact with the anus are the main sexual activities that transmit intestinal parasites, and for this reason it is very important to use dental dams or latex gloves during contact with the anus.

Infections caused by potentially sexually transmitted intestinal parasites include giardiasis, amebiasis, and cryptosporidiosis. Many people whose intestines are habitats to dangerous parasites are asymptomatic and could unknowingly infect their partners. Symptomatic individuals could experience diarrhea, abdominal pain or bloating, nausea, and vomiting. You can learn more about sexually transmitted intestinal parasites on our blog.

7 Molluscum contagiosum: Each year, hundreds of thousands of molluscum contagiosum infections are diagnosed. Symptoms can include small wartlike growths with an indentation in the middle. Molluscum contagiosum is a virus that can be transmitted sexually or nonsexually, through close, skin-to-skin contact. Most adults get it through sexual contact, but it can also be spread through other close contact as well as by sharing clothing or towels. Contact with the wartlike growths increases risk, so while it is always best to use latex barriers, such devices don’t always fully cover them. The best course of action is to avoid contact with these growths altogether, until they are removed or have cleared up. More information about molluscum contagiosum can be found on our blog.

6 Chancroid: Chancroid infections are rare in the United States, especially in Arizona, where our dry weather stands in stark contrast to the tropical climates where chancroid is more common. Symptoms of chancroid can include the formation of a swollen, open sore on the genitals. The lymph nodes in the genital region also become infected, and might swell to the point of breaking through to the skin’s surface, where they can release pus. Because the bacteria that cause chancroid can also be transmitted via oral sex, the infection can affect the oral cavity. Learn more about chancroid on our blog.

5 Cytomegalovirus: Also known as CMV, cytomegalovirus is incredibly common — about 80 percent of the U.S. population is estimated to be carriers, with about 4 in 10 of them infected nonsexually before puberty. Adults can be reinfected through sexual activity. Luckily, among healthy adults, a CMV infection usually does not have any symptoms, though if they do they are usually mild. CMV poses a greater threat to people who are pregnant or have compromised immune systems. The virus is present in urine, cervical and vaginal secretions, saliva, semen, blood, and breast milk. More information about CMV can be found on our blog.

4 Lymphogranuloma venereum: You’ve probably heard of chlamydia, which is caused by Chlamydia trachomatis. Most people don’t know that these same bacteria can cause a separate STD called lymphogranuloma venereum (LGV). While it’s not unknown in the United States, it is most common in tropical regions.

Like syphilis, LGV has three stages of infection:

  • primary stage: A small, usually painless, bump, ulcer, or lesion appears on the genitals. If the ulcer is located in the urethra, infection might be accompanied by a discharge.
  • secondary stage: Buboes can appear, and might be painful and enlarge to the point of bursting. (A bubo is an inflammation of a lymph gland, especially in the groin. The term bubonic plague was derived from that word, as buboes were especially salient symptoms of plague infections.) Other symptoms might include fever and acute hemorrhagic proctitis following anal intercourse. A three-week course of antibiotics during the second stage can prevent the infection’s progression to the tertiary stage, where it can do real damage.
  • tertiary stage: If Chlamydia bacteria continue to hang out in the infected tissue, the host can experience chronic inflammation, as well as other complications, including genital ulcers, fistulas, rectal strictures, and genital elephantiasis.

In the United States, there have been sporadic outbreaks of LGV. Sometimes LGV is brought here by Americans who have spent time in regions where it is endemic; there were small but significant increases in its prevalence in the United States during the Korean and Vietnam wars. More recently, there have been reports in Europe of outbreaks among populations of men who have sex with men. More information can be found at the CDC’s website.

3 Human T-cell lymphotropic virus: Abbreviated HTLV, in 1979 the strain HTLV-1 was the first retrovirus ever discovered (HIV is also a retrovirus). Worldwide, it is estimated that 15 million to 25 million people are infected with HTLV-1, and 4 percent of them develop adult T-cell leukemia lymphoma (ATL), a type of non-Hodgkin lymphoma. A protein encoded by this virus can interfere with our ability to repair DNA and regulate cell division, leading to uncontrolled growth of mutated cells. Its connection to a type of lymphoma makes HTLV one of a handful of cancer-causing sexually transmitted viruses, along with HPV and hepatitis B. Other than ATL, HTLV-1 can cause HAM/TSP, a chronic neurological disease; and infective dermatitis, a skin condition that mainly affects children. Heterosexual and male-to-male sexual HTLV-1 transmission has been documented. The virus is also spread by blood and breast milk. You can find information about ATL, with some information about HTLV-1, here.

2 Genital mycoplasmas: The term “genital mycoplasmas” refers to a category of several different species of sexually transmitted bacteria, most notably Mycoplasma genitalium. This species can cause nongonococcal urethritis (NGU) in people with penises, and it might also cause infections in people with vaginas. M. genitalium is considered an “emerging pathogen,” because despite its prevalence it is only over the past couple of decades that technology has allowed us to study this bacteria, along with other genital mycoplasmas.

Urethritis is an inflammation of the urethra, characterized by discharge, difficult or painful urination, or itching. When urethritis is caused by bacteria called Neisseria gonorrhoeae, the infection is called gonorrhea. Otherwise, it’s called NGU, which can be caused by several types of microorganisms. While Chlamydia trachomatis, the bacteria that causes chlamydia, is responsible for up to 40 percent of NGU cases, M. genitalium is responsible for up to 25 percent of NGU cases. (Less commonly, NGU can be caused by Trichomonas vaginalis; herpes simplex virus; and even the cold virus, which is associated with receptive oral sex.) As we expand our understanding of the various microbes and viruses that can cause NGU, we will improve our ability to treat these infections more effectively.

1 Donovanosis: Also called granuloma inguinale, donovanosis is a sexually transmitted bacterial infection. After the introduction of antibiotics, it has been rare in the United States, though it remains endemic in some parts of the world.

Although symptoms are usually mild, they aren’t always, and a quick Google search might net some alarming photographs of donovanosis infections. In most cases, the infection affects the genital area, though it can also affect the oral region, nose, and chest. There are four main types of donovanosis infections:

  1. ulcerogranulomatous: fleshy red ulcers that easily bleed
  2. hypertrophic or verrucous type: ulcer with a raised, irregular edge and a “walnut-like” appearance
  3. necrotic: deep, malodorous ulcer that causes severe tissue damage
  4. sclerotic or cicatricial: excessive scar tissue

More information on donovanosis can be found here.


The best way for sexually active people to avoid any STD — whether you’ve heard of it or not — is to use barrier methods, such as condoms and dental dams, consistently and correctly; and for new partners to be screened for STDs before initiating sexual activity. Planned Parenthood health centers can diagnose and treat STDs, from common infections like chlamydia to less-common ones like chancroid or intestinal parasites.

Click here to check out other installments of our monthly STD Awareness series!

2 thoughts on “STD Awareness: 10 Sexually Transmitted Diseases You Probably Don’t Know About

  1. Anna, I love how you’re always willing to talk about the STI’s folks know about . . . and the ones that are a little more under the radar.

    • The good news is that if you know how to protect yourself from chlamydia, HIV, and herpes, you also know how to protect yourself from cytomegalovirus, donovanosis, and genital mycoplasmas.

      Although I was really interested to learn that the cold virus can be transmitted to a penis! Skeptic that I am, I even confirmed it in several medical journals before posting. Wow.

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