Chapter 21: Sexually Transmitted Infections/Diseases

Welcome back to The Deep Dive.

Today, we're undertaking a pretty critical deep dive into Chapter 21.

We're really zeroing in on how microorganisms affect human health, specifically looking at sexually transmitted infections, or STIs.

That's right.

We've got a good stack of sources here, and the idea is to, you know, cut through some of the complex clinical stuff, give you a clear guide to the different pathogens, the damage they can cause, and why these infections are still such a major public health issue.

Absolutely.

And we need to map out the territory first.

Exactly.

We're looking at four main types of culprits here.

Bacteria, viruses, fungi, and protozoa.

Each one works differently, attacks the body differently, and crucially needs a different treatment approach.

And let's nail down the language right at the start, because the terms really matter here.

We often talk about STIs, sexually transmitted infections.

That just refers to, well, the pathogen being there in the body.

Right.

The person might not have any symptoms at all.

It's just the presence of the organism.

But then there's STD, sexually transmitted disease.

And that's the key difference.

STD means symptoms have shown up.

There's actual damage happening because of the infection.

We'll mostly use the term STI today.

It's broader, but keep that distinction in mind.

Infection can be present and spreading completely silently.

It's a silent challenge.

And history shows us it's definitely not new.

We're talking thousands of years back.

Oh, yeah.

Ancient Babylon, for instance.

They thought STDs were like the wrath of the gods of love.

And Hammurabi's code.

Wasn't there something in there?

There was.

It describes an evil disease causing sores.

Infertility sounds a lot like advanced syphilis, even back then.

Wow.

Which brings us to a more modern, infamous example.

Al Capone.

Right.

The law couldn't quite pin him down completely, but tertiary syphilis did.

He contracted it years earlier, and it eventually destroyed his vital organs.

He died from it in 1947.

It's a powerful reminder that biology has the last word sometimes.

Definitely sets the stage.

So let's look at the scale of this today.

The CDC numbers are just huge.

Prevalence, that's the total number of people living with an STI right now in the US, is around 110 million.

110 million.

And the incidence, so the new case is diagnosed each year, that's hovering around 20 million.

And the cost is enormous.

Something like 16 billion dollars annually to the US healthcare system.

What's driving those numbers?

The sources mentioned younger people being sexually active earlier.

That's a factor, yeah.

And also, increasing numbers of sexual partners contribute significantly to the transmission rates.

Okay, let's zoom in on the biology.

Why the reproductive system?

Why is it more vulnerable than, say, the skin on your arm?

It really comes down to the anatomy.

The reproductive organs, for the most part, aren't lined with tough skin like your arm is.

They're lined with mucous membranes.

And these membranes, they lack that really robust protective outer layer that skin has, so pathogens can penetrate much more easily.

Making them prime entry points during sexual activity.

Exactly.

Perfect entry points for bacteria, viruses, you name it.

Okay, so let's transition into the first big category then.

The bacterial STIs.

We often hear about the big three here.

And the key thing, the big takeaway, is that these are treatable with antibiotics, right?

They are treatable, yes.

But here's the

any damage done before treatment.

That's often permanent.

Think infertility, organ damage.

A tragic irony, really.

Yeah.

Treatable, but the consequences can last a lifetime.

Precisely.

Let's start with gonorrhea.

It's actually the most reported STI in the US, caused by Neisseria gonorrhea.

And for the micro students listening, that's a gram negative diplococcus.

Pairs of bacteria, stain pink in the gram stain, known for being tricky.

And I found this surprising fact about N -gonorrhea.

We usually think bacteria are fragile outside the body, but apparently some of these strains can survive for over a month, like in dried pus on bedding.

Yeah, that resilience is pretty concerning.

It definitely complicates things like tracing contacts, and it links directly to how it spreads, because gonorrhea is often, well, asymptomatic.

A silent spreader.

How common is that, being asymptomatic?

Very common.

Somewhere between 60 and 80 % of infected females, and maybe up to 40 % of males, might show no symptoms at all.

They can carry it and spread it for years without knowing, letting that internal damage accumulate.

So if symptoms do show up, what are we looking at?

Typically, discharge.

Painful urination, especially in men.

But the real danger lies in the complications if it's left untreated.

By spreading through the body.

Exactly.

Systemic infections like endocarditis inflammation of the heart lining or arthritis.

And locally, in men, it can cause epididymitis, inflammation of the tubes connected to the testes.

That often leads to infertility.

And in women?

It's a major cause of pelvic inflammatory disease, PID.

That scars the fallopian tubes.

Huge risk for ectopic pregnancies later, or again, infertility.

You mentioned skin lesions too.

Yes, if it spreads systemically.

They start as small red bumps, erythematous papules, then develop these necrotic grayish centers.

Pretty distinct if you see them.

How is it diagnosed now?

Is it still cultures?

Less often.

Cultures are being replaced by nots nucleic acid amplification tests.

These are highly accurate genetic tests looking for the bacteria's DNA or RNA.

Much faster, more sensitive.

And treatment.

Penicillin used to be the go -to.

It was.

But resistance is a massive problem now.

So current guidelines usually recommend other antibiotics like ciprofloxacin or azithromycin.

Sometimes a combination.

Okay.

That naturally leads us to number two of the big three.

Syphilis.

The great imitator.

Caused by trypanema pallidum, a gram -negative spirochete.

Looks like a little corkscrew under the microscope.

And it gets that imitator name because its symptoms can look like so many other conditions.

It's tricky.

It's known for its stages, right?

Three distinct phases.

Correct.

It progresses if untreated.

Stage one is primary syphilis.

This starts with a small, typically painless sore called a chancre.

Usually appears right at the site where the bacteria entered the body.

And the dangerous part here is that this chancre, it just goes away on its own, doesn't it?

It does.

Usually heals within a few weeks, even without treatment, which gives a false sense of security.

So people think they're fine, but the bacteria is still there.

Exactly.

And then maybe two to 10 weeks after the chancre disappears,

secondary syphilis kicks in.

The spirochete has spread into the bloodstream now.

This is when you get the more systemic symptoms.

Like the classic rash.

Yes, a very characteristic red -brown rash, often appearing on the palms of the hands and the soles of the feet.

You might also get fever, muscle aches, joint pain, swollen lymph nodes.

Still treatable at this stage.

Yes, definitely.

But if it's still not treated, it enters a latent phase.

Can be months, years, even decades, and then it can potentially erupt into the really devastating tertiary stage.

This is the alcapone phase.

This is the alcapone stage.

This is where you see the development of gummas.

These are large, rubbery masses of dead and inflamed tissue.

They can form in skin, bones, and crucially in vital organs like the heart or brain.

Leading to, well, catastrophic problems.

Catastrophic is the right word.

Neurological damage causing memory loss, paralysis, personality changes, blindness, insanity, and ultimately death.

So diagnosis is critical.

How is it confirmed?

Usually requires two different types of blood tests to be sure.

Tests like the VDRL or RPR are common screening tests, often followed by a more specific treponemal test for confirmation.

And the good news, treatment -wise.

The good news is, if caught in the primary or secondary stage, a single intramuscular shot of long -acting penicillin G is usually curative.

It's still highly effective for early syphilis.

Tertiary syphilis is harder to treat,

though.

Okay.

Let's move to the third, the big three, chlamydia.

Caused by chlamydia trecomatis.

Now this one's biologically interesting.

It's an obligate intracellular parasite.

Meaning it has to live inside our cells to reproduce.

Exactly.

It can't survive or replicate outside of a host cell.

And statistically, this is the most prevalent bacterial STI in the U .S.

More common than gonorrhea.

Yes.

Significantly more common, though reporting rates might vary.

It truly is the silent epidemic.

The asymptomatic rate here is incredibly high.

Up to 80 % of infected women, maybe around 50 % of men, show zero symptoms.

Wow.

80%.

That's huge.

It is.

And that massive pool of undiagnosed asymptomatic carriers is a major reason why it spreads so easily.

It also increases a person's susceptibility to other STIs like HIV.

And the complications are similar to gonorrhea, PID epididymitis.

Yes.

It's a leading cause of both pelvic inflammatory disease in women and epididymitis in men.

Contributing heavily to infertility.

But there's a specific type, LGV, that looks quite different, right?

Lymphogranuloma venerium.

Right.

LGV is caused by certain strains of chlamydia trecomatis.

With LGV, you might get an initial small sore or lesion, which often heals and might go unnoticed.

But then the bacteria invade the lymph nodes in the groin area.

This causes them to swell up massively, forming these large, painful lumps called buboes.

Buboes, okay.

And if these aren't drained or treated effectively, the chronic inflammation can lead to severe permanent swelling and disfigurement of the genitals.

Really quite dramatic.

Diagnosis for chlamydia.

Also, neuloses.

Yes.

Nut ats are the gold standard now.

Highly sensitive and specific for detecting chlamydia DNA or RNA.

There are even automated systems like one called Tigris DTS used in labs for rapid high -volume testing.

Okay, so those are the big three.

We should probably quickly touch on a few other bacterial STIs mentioned in the chapter.

Definitely.

There's mycoplasmal and ureaplasmal non -gonococcal urethritis, NGU,

caused by mycoplasma hominis and ureaplasma ureoliticum.

The key thing about these organisms, they don't have a cell wall.

Which means penicillin won't work.

Exactly.

Penicillin and related antibiotics target cell wall synthesis, so they're completely ineffective against mycoplasmas and ureaplasmas.

In ureaplasma, ureoliticum is actually implicated in a huge chunk of infertility cases, maybe over half of cases where a microbe is the suspected cause in a couple.

That's significant.

Then there's chancroid.

Right.

Caused by hemophilus ducre.

The key difference here is the type of chancre or sore it produces.

Remember, syphilis causes a hard,

painless chancre.

Chancroid causes soft, painful chancres that bleed really easily.

That distinction is important for diagnosis.

Got it.

Soft and painful versus hard and painless.

And donovanosis.

Donovanosis caused by Klebsiella granulomatis.

This one has a very specific diagnostic clue under the microscope.

You look for something called donovan bodies.

These are the bacteria encapsulated seen inside macrophages, and they often look like tiny closed safety pins.

Very distinctive visual.

A visual clue for the lab techs.

And one last bacterial note, toxic shock syndrome.

Yes.

Important to mention that certain strains of MRSA, methicillin -resistant staphylococcus aureus can actually be sexually transmitted.

And S aureus is the bacteria responsible for toxic shock syndrome.

So there's a potential link there.

Okay.

So that covers the bacterial side.

Treatable, but potentially leaving lasting damage.

Now we pivot.

Now we pivot to a fundamentally different challenge.

The viral STIs.

And the key word here shifts dramatically, doesn't it?

From curable to.

To incurable, unfortunately, at least with current medical technology.

Viral STIs can be managed with antiviral drugs, often very effectively, but the virus itself generally can't be eliminated from the body.

It persists.

The biggest name here obviously is HIV.

Human immunodeficiency virus.

Right.

HIV's primary target is the immune system itself.

Specifically, it attacks and destroys crucial immune cells, particularly the helper T cells, also known as CD4 cells.

And destroying those cells is what leads to AIDS.

Exactly.

As the helper T cell count drops, the immune system becomes progressively weaker.

Eventually it reaches a point where the body can't defend itself against infections and cancers that a healthy immune system would normally handle easily.

That stage of severe immune deficiency is defined as acquired immunodeficiency syndrome or AIDS.

People with AIDS become vulnerable to opportunistic infections like Kaposi's sarcoma, severe candidiasis, cytomegalovirus infections, and others.

Diagnosis for HIV has a specific process too, right?

Yes.

It's usually a multi -step process for accuracy.

It often starts with a screening test, like the ELISA test.

It's sensitive and relatively inexpensive.

If the ELISA is positive, it needs to be confirmed with a more specific test, usually the Western blot.

Together, that sequence is extremely accurate, like 99 .9%.

Are there other tests?

Yes.

HIV PCR tests can detect the virus's genetic material, DNA, or RNA directly.

These are useful for early detection or monitoring viral load.

And there are home tests available now too, like Orishir, which uses saliva samples from the cheek or gums.

And treatment has come a long way, but it's not a cure.

Not a cure, no.

But treatment is highly effective at suppressing the virus.

It usually involves taking a combination of antiviral drugs, often called a cocktail.

There are seven different classes of these drugs approved.

Things like nucleoside reverse transcriptase inhibitors, NRTIs, non -nucleoside reverse transcriptase inhibitors, and NRTIs, protease inhibitors, and others.

They work in different ways to stop the virus from replicating.

But finding a cure or a vaccine is still proving incredibly difficult.

It is.

A major reason is that HIV mutates extremely rapidly.

It changes its structure constantly, making it very hard for the immune system or a vaccine to target it effectively.

Experts think a cure or a widely effective vaccine is likely still decades away.

Okay, besides HIV, the chapter covers hepatitis viruses as STIs too.

Right.

Hepatitis just means inflammation of the liver.

Several viruses can cause it, and some can be transmitted sexually.

They cause significant liver cell destruction.

We need to differentiate B, C, and D.

Yes.

Hepatitis B virus, this one is preventable, there's a safe and effective vaccine available.

It's usually given us three shots over about six months.

Good news there.

What about hepatitis C?

Hepatitis C virus, HCV, is more problematic long -term.

A large percentage, maybe 70 -80 % of people with acute HCV infection go on to develop chronic hepatitis.

This can lead to cirrhosis, liver cancer, and crucially, there is currently no vaccine for hepatitis C.

And hepatitis D.

Hepatitis D, HDV, is interesting.

It's a defective virus.

It actually needs hepatitis B virus to be present in order to replicate.

So you can only get HDV if you already have HPV.

Preventing HPV with the vaccine also prevents HDV.

Okay.

Moving on to another very common viral STI, genital herpes.

Caused by herpes simplex virus, either type 1, HSV1, or type 2, HSV2.

Highly contagious.

It causes recurrent outbreaks of painful blisters or sores in the genital area.

A major concern with herpes is during pregnancy and delivery.

Neonatal herpes.

Exactly.

The virus can be transmitted to the baby during childbirth if the mother has an active outbreak.

This can cause severe neurological damage, mental retardation, blindness, or even be fatal for the newborn.

It can sometimes cross the placenta too, potentially causing spontaneous abortion.

And the last major viral one mentioned?

HPV.

Human papillomavirus.

HPV is incredibly common.

In fact, it's considered one of the most common STIs globally.

Often, it's completely asymptomatic.

Most people with HPV don't even know they have it.

But what it does cause problems.

It can manifest in two main ways.

Some strains cause genital warts.

These are growths that can appear on the genitals or anus, sometimes described as having a cauliflower -like shape or texture.

Other strains, however, are much more dangerous.

These are the high -risk HPV types that can cause cancer.

Primarily cervical cancer in women.

Primarily cervical cancer, yes, but also cancers of the vulva, vagina, penis, anus, and even the back of the throat.

But there's a huge prevention success story here, isn't there?

There is.

The development of HPV vaccines, like Gardasil, has been a major public health achievement.

These vaccines protect against the most common HPV types that cause both genital warts and cancers.

The recommendation is for both boys and girls to get vaccinated, ideally around age 11 or 12 before they become sexually active, for maximum protection.

Okay, that covers the viral challenges.

Let's quickly round out the picture with the other categories.

Fungal and protozoan and STIs.

Right, starting with fungal infections.

The main player here is usually candida, a type of yeast.

Causing yeast infections?

Commonly, yes.

Vulvavaginal candidiasis in women, often presenting with that thick, white, curd -like discharge and itching.

It can also cause balanitis in men, which is inflammation of the head of the penis, more common in uncircumcised males.

And Tadeucurus or Jdokic, though often caused by other fungi, can sometimes involve candida and be transmitted sexually.

Is diagnosis straightforward?

It can sometimes be tricky, because candida is often normally present in small amounts as part of the body's natural microflora.

So just finding it doesn't always mean it's the cause of the symptoms.

You have to consider the clinical picture, the quantity of yeast present.

Okay.

And finally, the protozoan STIs.

There's really only one significant protozoan STI, trichomoniasis, caused by trichomonas vaginalis.

How common is this one?

Surprisingly common.

The chapter notes its incidence might actually be as high as, or even higher than, gonorrhea and chlamydia combined.

But because it's often considered mild and isn't a nationally reportable disease in the same way, it often flies under the radar.

What are the symptoms if they appear?

In women, it causes a very characteristic vaginal discharge, typically frothy, yellow -green, and often with a strong, unpleasant fishy odor.

There can also be itching and irritation.

And in men?

Men are frequently asymptomatic carriers.

They might have mild urethritis sometimes, but often they have no symptoms at all, making them unknowing transmitters.

Even if it's considered mild, are there any serious concerns?

Yes, especially during pregnancy.

Trichomoniasis has been linked to an increased risk of preterm delivery and having a low birth weight baby.

So it's definitely not something to dismiss, despite its reputation.

Okay, so let's try to synthesize all of this.

It's a really diverse landscape of pathogens.

It really is.

Bacteria, viruses, fungi, protozoa, all causing SPIs.

The absolute key distinction to remember is between the bacterial infections and the viral ones.

Bacterial STIs like gonorrhea, syphilis, chlamydia, generally curable with antibiotics.

But, and it's a big but, the damage done before treatment, like infertility or organ damage, is often permanent.

Whereas the viral STIs, HIV, herpes, HPV, hepatitis BC, are currently incurable.

Right.

They can be managed often very well with antiviral medications, but the virus stays with you.

And the overall prevalence of all these STIs remains a massive, costly, and complex public health challenge around the world.

Understanding the specifics, like how HIV targets T cells or how chlamydia needs to be inside a cell, that really helps understand the clinical picture, doesn't it?

Absolutely.

Knowing the mechanism is key to understanding the disease and the treatment strategies.

So let's leave our listeners with a final thought to chew on.

We've talked a lot about asymptomatic infections, chlamydia, gonorrhea, HPV, herpes,

even HIV initially.

Many of these, especially the most common ones, often show no symptoms for a long time or ever.

How does knowing about this silent spread change how you think about the need for regular testing and awareness, even if you feel perfectly fine?

It highlights that it's not just about waiting for symptoms, it's about recognizing the potential silent presence of infection before irreversible damage occurs or before it's passed on.

A really crucial point.

Well, thank you for joining us for this deep dive into the microbiology of STIs.

Anna Warham, thank you from the Last Minute Lecture team.