From creepy crawly pubic lice, which can be seen with a magnifying glass, to minuscule human papillomaviruses, which can be seen with some of the most expensive microscopes in the world, there are many tiny pathogens that we can acquire through sexual contact. And, despite their diminutive sizes, some of them work in complicated ways, or tell stories about our origins that would blow you away. Let’s learn some amazing facts about three sexually transmitted bugs!

Image: Public Health Image Library

Pubic lice: tiny insects that live in pubic hair

Fans of Charles Darwin might like learning about pubic lice, which offer clues about human evolution. While other apes’ bodies are habitat to only one species of louse, human bodies can host three different types of louse: head lice and the closely related body lice, as well as the distantly related pubic lice.

It is thought that when early humans lost their body hair, human lice followed this receding hairline and migrated to their heads to become head lice. At a later date, the gorilla louse colonized early humans’ pubic regions. Since pubic lice can be transmitted by infested bedding, one idea is that an early human caught pubic lice by sleeping in a burrow that had been recently vacated by a lice-ridden gorilla — no sexual contact required.

By examining the number of differences in the genetic codes of the modern gorilla louse and the human pubic louse, we can place their divergence into two separate species at about 3 million years ago, suggesting that our human ancestors lost their body hair at around that time.

A quite frankly weird fact about pubic lice involves the method their young use to hatch from their eggs — by releasing so much gas that the increase in air pressure causes them to burst from their shell. So there’s that.

Image: Antonio Pereira-Neves & Marlene Benchimol, Santa Ursula University

Trichomonas vaginalis: the most common sexually transmitted pathogen you’ve probably never heard of

Quick, what’s the most common curable STD in the country? Most people have no idea. Many other people would guess chlamydia, which infects 2.86 million Americans annually. But it’s actually an infection called trichomoniasis, or trich for short, which most people haven’t even heard of — despite striking 7.4 million Americans every year!

Trich is caused by a parasite called Trichomonas vaginalis, which is an “animal-like” organism that, like a bacteria, gets by with just one cell. But despite its unicellular status, it’s much more complicated than a bacterium — and much larger. In fact, these parasites eat bacteria for breakfast — and lunch and dinner! The above image shows a T. vaginalis organism, in green, chilling out on a human cell amid a few purple-colored bacteria, which are tiny in comparison.

Unfortunately, T. vaginalis is making those aforementioned Darwin fans pretty giddy by proving that evolution is a fact of life: Slowly, they are evolving resistance to the drugs we use to treat them, although currently drug-resistant strains are rare. However, trich drugs are chemically similar, which makes some researchers wary — if T. vaginalis keeps honing its resistance to them, we might not have viable alternatives in the future.

If you are treated for trich, take the full course of drugs that you are prescribed — don’t stop early, even if symptoms have disappeared. Otherwise, a few especially tough organisms might be hanging in there, giving rise to descendants who are just as tough as they are — Darwin called it survival of the fittest.

Image: University of Arizona

Human papillomavirus: the virus that causes genital warts and certain cancers

Human papillomavirus (HPV) is known as the “common cold of STDs” — because nearly every sexually active person will contract it, even people with few sex partners. Despite only having a total of eight genes (whereas humans have several thousand), HPV can pack a mighty punch. Most people don’t have symptoms, but certain strains of HPV can cause warts, while other strains can cause cancers of the cervix, anus, throat, and penis.

Two things you need to know about the human body in order to understand how HPV is able to cause cancer:

• Our bodies are able to attach a “tag” to a protein to mark it for destruction. These tagged proteins are destroyed.
• We also all have proteins called p53, which can suppress the formation of tumors. These proteins are important components of our immune system, and help ward off cancer.

Cancer-causing HPV produces a protein that can physically interlock with both the “tags” that mark a protein for destruction as well as the tumor-suppressing p53 proteins — effectively linking them together into one unit. This tricks the body into destroying both the viral protein as well as the tumor-suppressing p53 protein that is attached to it — and, without the protection given us by p53, we’re left that much more vulnerable to developing tumors. Luckily, most strains of HPV don’t cause cancer — they just cause warts, which is by far the lesser of two evils.

Why did I organize this post the way that I did, as a Top 3 list? Didn’t David Letterman share Top 10 lists when he wanted to get laughs? Aren’t I making light of serious diseases by presenting them as a list of fun facts?

Fear or embarrassment can make it difficult for people to talk to their partners about their sexual history or safer sex. They can also make individuals less likely to get STD testing. Shame and stigma can bring huge emotional burdens to those who have caught an STD. The taboos that surround sex and disease aren’t good for anybody — not for their health, not for their self-esteem.

My hope is that I can show you how interesting sexually transmitted pathogens can be, strictly from a biological perspective. If people can get used to talking about the pubic louse’s role in our discoveries about human evolution, or the wily way that HPV tricks our bodies into destroying their own anti-tumor cells, maybe those same people will find it that much easier to talk about STD testing, their STD status, or HPV vaccination with their sexual partners.

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