Chapter 14: Spirochetes

Welcome to Last Minute Lecture.

This free chapter overview is designed to help students review and understand key concepts.

These summaries supplement not replaced the original textbook and may not be redistributed or resold.

For complete coverage, always consult the official text.

Welcome back to the Deep Dive.

Today we are pulling something off the shelf that I think a lot of people might recognize, especially if they've ever frantically crammed for a medical board exam.

Oh yeah.

We are cracking open clinical microbiology made ridiculously simple.

A classic.

It really is.

It's one of those books that promises a lot with its title because microbiology is usually anything but simple.

It's usually a swamp of Latin names and microscopic details.

Exactly.

And today we're testing that promise.

We're diving specifically into chapter 14.

We are taking on the Spirochetes.

Now for the uninitiated, Spirochete sounds like a type of pasta, but I have a feeling it's something much more sinister.

You definitely don't want to eat these.

Yeah.

The name Spirochet is actually a morphological description.

Okay.

It comes from the Greek for coil and hair.

So these are spiral shaped corkscrew like bacteria and that shape isn't just for show.

It's very functional.

How so?

What does the shape do?

Well most bacteria just sort of float or tumble.

Okay.

But Spirochetes, they drill.

They drill.

They have these internal structures called axial filaments that allow them to corkscrew their way through viscous environments like say mucus or connective tissue where other bacteria would just get stuck.

So they are microscopic drill bits.

That is a terrifying image to start with.

It is, but it's effective.

And that brings us to our mission for this deep dive.

This chapter focuses on the big three genera of this family.

The big three.

Trypanema, Borrelia, and Leptospora.

Right.

And the challenge, the reason students usually hate this chapter, is that clinically these bugs can look very different, but microbiologically they're cousins.

So they're related, but they cause completely different problems.

Exactly.

And the goal today is to walk through the book's specific visual cues, the cartoons, the flow charts, the mnemonics, so that we can distinguish between the stages of

syphilis and Lyme without getting a headache.

I love that.

We aren't just memorizing lists.

We are building a visual memory palace.

That's the idea.

We've got sharks.

We've got surfers.

We've got gummy bears.

We've got limes.

It sounds like a fever dream, but we are going to make sense of it.

Let's do it.

All right.

Let's start with the heavy hitter, the most famous or perhaps infamous member of the family.

That would be Trypanema pallidum.

The causative agent of syphilis.

Not detailed timeline flow chart.

And I think the timeline is the most important part because syphilis seems to be a story with different chapters.

That's the perfect way to view it.

It's a progression.

And if you don't know which chapter of the story you're in, you'll miss the diagnosis.

So where does the story start?

The flow chart begins at the very beginning transmission,

which it lists as sexual contact.

Correct.

It is a sexually transmitted infection.

The bacteria enter through tiny abrasions in the skin or mucous membranes during contact.

But here's the first trick syphilis plays on you, which is you don't get sick immediately.

The chart lists an incubation period of three to six weeks.

That is a long time.

That's a month or more of silence.

The bacteria are replicating.

They're drilling in, but you feel completely fine.

You have no idea you've been infected.

And then after that month or so, we hit the first big box on the chart.

Primary syphilis.

This is act one.

And the star of act one is the ulcer.

The text calls it a chancre.

It's chancre, yes.

But there's a very specific adjective attached to it that the book highlights.

Painless.

Why is that distinction so important?

Because pain is usually what drives people to the doctor.

I mean, if you have a painful sore like herpes or a chancroid, you notice it immediately.

You seek help.

Of course.

But a syphilis chancre is a clean, indurated ulcer that does not hurt.

If it's in a spot you can't easily see, like the cervix or inside the anal canal, you might not even know it's there.

So you could have primary syphilis and be totally unaware.

Absolutely.

And here is where it gets even trickier.

Look at the arrow pointing away from the primary syphilis box.

It says, ulcer heals after four, six weeks.

It heals spontaneously without treatment.

Wait, so the body cures it.

Is that what's happening?

No, that is the track.

Okay.

The local immune response manages to clean up the surface ulcer so the skin heals.

And if a patient did notice the sore, they might see it go away and think, oh, thank goodness it was nothing.

I'm fine.

But they aren't fine.

Not at all.

The disappearance of the ulcer is just the end of Act 1.

While the skin was healing, the spearshites were entering the lymphatics and the bloodstream.

They were escaping.

They were spreading systemically.

This leads to another silent period, about six weeks before the curtain rises on Act 2.

Secondary syphilis.

Now this is where the book's visual mnemonics really kick into high gear.

We are looking at Image 2.

Describe this for me because it's weird.

It is weird.

It's a drawing of a moon, a purple cratered moon surface.

And there's a speech bubble coming out of the moon that says, wee, like someone going down a roller coaster.

Exactly.

Wee.

Okay, unpack this.

Why is the moon yelling wee?

It's a double layered mnemonic.

First, let's look at the moon itself.

It has craters.

This represents the lesions.

Right.

Secondary syphilis is characterized by widespread lesions and rashes, but the sound effect is the key.

Think about the word wee, W -E, as in us.

Okay.

In primary syphilis, the infection was local.

It's just me.

In secondary syphilis, it's systemic.

It's everywhere.

It's us.

It's in the whole body.

Well, I like that.

Wee means systemic.

That's clever.

And the second part of the wee is the sound of sliding or moving fast.

It implies the rapid dissemination of the bacteria throughout the bloodstream.

It's going everywhere.

So when you see the moon, you think systemic spread.

Okay.

Now let's look at the clinical features listed in this moon box on the flow chart.

Because since it's systemic, it seems like it affects everything.

It really does.

The chart lists fever, weight loss, and generalized lymphadenopathy.

Which basically sounds like flu or mono.

Pretty much.

Generalized lymphadenopathy just means swollen lymph nodes all over the body, neck, armpits, groin.

That's a sign that the immune system is fighting a war on multiple fronts.

But then we get to the specific signs.

The chart highlights red rash, especially palms and soles.

This is a high yield fact.

If you are taking notes, circle this.

Okay.

There are very, very few diseases that cause a rash specifically on the palms of your hands and the soles of your feet.

Rocky mountain spotted fever, hand foot and mouth disease, and secondary syphilis.

That's the short list.

So if someone comes in with flu symptoms and you check their hands and see red spots on their palms, your internal alarm bells should be screaming syphilis.

It's a classic presentation.

The chart also mentions hair loss, alopecia, and it's often described as moth eaten alopecia.

It looks like little patches of hair have just been snipped out of the scalp or eyebrows.

Wow.

Okay.

And then there's this term condylomolatum.

Yeah.

It sounds like a spell from Harry Potter.

It does.

Condylomolatum.

The chart describes these as moist warty patches in the genitals or skin folds.

How is that different from regular genital warts?

Great question.

Regular genital warts, which are caused by HPV, are usually spiky or cauliflower -like.

Condylomolatum are flatter, broader, and moist.

Okay.

And here is the scary part.

They are absolutely packed with spear sheds.

So they are contagious.

Extremely.

In the secondary moon stage, the patient is highly infectious.

So we have the flu, we have palm rash, we have patchy hair loss, and we have infectious warts.

How long does this horror show last?

The chart says two to six weeks, and then just like the primary ulcer, it can resolve on its own.

It goes away again.

It goes away again.

The immune system suppresses the bacterial load, but look at the left side of the chart.

There's a loop.

It says 25 % relapse to secondary.

Right.

So for about a quarter of patients, they get stuck in this loop.

They get better.

Then a few months later, the rash comes back.

They get better.

It comes back.

It's a relapsing course.

Okay.

But eventually, for the majority of untreated people, the symptoms fade for good, and we enter the next phase.

The silent phase.

The flow chart leads down to a box labeled latent.

Latent syphilis.

The bacteria are still in the body.

If you tested their blood, they would be positive, but they have no symptoms.

None at all.

None.

They aren't contagious anymore usually, and they feel fine.

And this is where the flow chart introduces the rule of thirds.

This seems to be the way to predict what happens to these untreated people.

Yes.

This is based on studies from before we had antibiotics.

This was the natural history of the disease.

So let's do the math.

Outcome number one.

The chart shows that 23 or so, roughly 66 % of latent cases result in or maintenance.

What does that mean?

Maintenance.

Basically, the body reaches a stalemate with the bacteria.

The person never gets sicker.

They live their lives, maybe never knowing they have it, but they don't develop the horrific late stage symptoms.

That is surprisingly high.

I think the pop culture understanding of syphilis is that it's always a death sentence if you don't treat it.

Not always, but you definitely don't want to take the risk because of the remaining 13.

The unlucky 33%.

The arrow points down to tertiary syphilis, and the timeline here is wild.

It says six to 40 years.

That is a massive window.

You could get infected in your 20s during a wild summer and not develop tertiary syphilis until you are retired in your 60s.

Wow.

It is a slow, chronic burn.

And to illustrate what happens in tertiary syphilis, the book gives us another incredible cartoon.

Image two, the bottom half.

We have a bone and block of skin,

and inside them are literal gummy bears.

Yes, the red gummy bears.

This is visualizing the term gummas.

Gummas, G -U -M -M -A -S.

A gumma is a specific type of granuloma.

It's a ball of immune cells trying to wall off the bacteria, but in the center, the tissue dies and becomes soft and gummy.

Like necrotic tissue.

Exactly, hence the name.

So you literally have dead tissue balls forming in your body.

Exactly.

And the cartoon puts them in the bone and skin because those are classic sites.

These things are destructive.

A gumma can eat a hole through the roof of your mouth.

It can destroy the bridge of your nose, leading to that saddle nose deformity you see in old textbooks.

That is horrifying.

Gummy bears in the bone is an image that is going to stick with me.

Good.

That means it's working.

And about 15 % of those who progress to tertiary syphilis will develop these gummas.

But the damage isn't limited to gummy bears.

The chart splits into two other paths for tertiary syphilis.

Next, we see a heart.

Cardiovascular syphilis.

This affects about 10 % of patients.

And notice the arrow points specifically to the aorta.

Why the aorta?

What's special about it?

The bacteria cause inflammation of the tiny blood vessels that supply the aorta wall itself.

It's a condition called aortitis.

This weakens the wall of the aorta.

So it gets stretched out.

It can stretch out, leading to an aneurysm.

The classic description is that the inside of the aorta starts to look like tree bark.

Tree bark aorta.

And if that aneurysm bursts, it's often fatal.

And the final path, the brain.

Neurocyphilis.

About 8 % of cases, this is where the infection attacks the central nervous system.

It can cause dementia, personality changes, delusions of grandeur.

It's what people used to call general paresis of the insane.

Speaking of the nervous system, there's one specific type of damage mentioned in the context of congenital syphilis, but it relates to this.

We have image 3, which is a cross -section of a spinal cord.

Right.

This is a very specific anatomical lesson.

The diagram highlights the dorsal roots and the posterior columns of the spinal cord.

For those of us who aren't neurologists, what do those parts do?

So the posterior columns are the highways for position -sense proprioception.

It's what tells your brain where your feet are with how you're looking at them.

And syphilis attacks that highway.

It selectively destroys it.

This condition is called Tebiz dorsalis.

Because these patients can't feel where their feet are landing, they develop a very distinct walk.

Oh, so.

They lift their legs high and slap them down hard on the ground.

The slapping gait.

Right.

They are slapping their feet to feel the vibration just to know where the floor is.

It's a tragic late -stage complication.

We should also briefly touch on congenital syphilis since you mentioned it.

That's when a mother passes the infection to the fetus.

Yes.

The spirushadies can cross the placenta.

This is why prenatal screening is mandatory in so many places.

The damage to a developing fetus is severe.

What kind of damage?

It can cause stillbirth.

Or if the baby survives, they can have distinct deformities like saber shins where the shin bone bows forward.

Or Hutchinson's teeth where the incisors are notched.

It's a heavy list of consequences.

So we have tracked this bug from a three -week incubation to a healing ulcer to a wee moon rash into a decades -long silence and finally to gummy bears and heart failure.

That is a journey.

It is.

But the good news is we can catch it.

We don't have to let it get that far.

Right.

The chapter has a section on diagnostic tests.

And this is where the medical students usually start sweating because it's an alphabet soup.

Right.

VDRL, RPR, FTA, ABS.

It is confusing, but let's simplify the strategy.

The text groups these tests into two categories, screening and confirmatory.

Okay.

Let's start with the screening tests.

That's the VDRL and RPR.

Right.

These are non -tropenemal tests.

That means they aren't looking for the bacteria itself.

What are they looking for then?

They are looking for a biomarker, specifically antibodies against a substance called cardiolipin, which is released when cells are damaged by the infection.

So they are indirect.

Exactly.

They are cheap and fast, which makes them good for screening a lot of people.

But because they are indirect, they can be tricked.

Other things can cause cell damage and release cardiolipin.

So you can get a false positive.

Yes.

And the book gives us a mnemonic for false positives using the letters VDRL.

Let's hear it.

Okay.

V is for viruses like mono or hepatitis.

D is for drugs.

R is for rheumatic fever.

And L is for lupus or leprosy.

So if a patient has mono or lupus, they might test positive for syphilis on a VDRL test, even if they don't have it.

Exactly.

That's why you never, ever diagnose syphilis based on just an RPR VDRL.

If that test is positive, you have to move to the second group.

The confirmatory tests, the FTA -ABS.

This is a tropenemal test.

It looks specifically for antibodies against the tropenema bacteria itself.

It's much more specific.

If this is positive, it confirms the diagnosis.

So the strategy is screened with RPR.

If it's positive, confirm with FTA -ABS.

You got it.

That's the two -step process.

Now, before we leave syphilis, there is one more phenomenon mentioned.

It's in a blue header, the Juris -Herxheimer phenomenon.

That is a mouthful.

It is a mouthful, but it's a classic board exam question and a very real clinical event.

Imagine you have a patient with confirmed syphilis.

You give them the correct treatment, usually a shot of penicillin.

Okay.

So you're treating them.

Two hours later, the patient starts shaking.

They get a high fever, chills, muscle pain, and their blood pressure drops.

The immediate thought would be, oh no, they're allergic to the penicillin.

I've killed them.

Exactly.

And that is the mistake you must not make.

The Juris -Herxheimer reaction is not an allergy.

It's not.

What is it then?

It is actually a sign that the antibiotic is working too well.

Too well.

How can it work too well?

You have just killed millions and millions of spirits instantly.

As they die, they burst open.

They release all their toxins and inflammatory markers into the blood at the same time.

It's a death burst.

That's a perfect way to describe it.

The immune system sees the sudden flood of bacterial debris and freaks out.

It releases a storm of cytokines causing the fever and chills.

So what do you do?

Do you stop the penicillin?

No.

You absolutely continue the treatment.

You give them fluids, maybe some Tylenol for the fever, and you reassure them it passes in a few hours.

Good to know.

Don't panic.

It just means you're winning the battle.

Precisely.

All right.

Treponema pallidum gets all the fame, but the chapter points out that the treponema family has some other members.

It does.

And the cartoons for these are, well, they are graphic.

They're vividly memorable.

These are the non -venereal treponemas.

They are subspecies of treponema pallidum.

Genetically, they're almost identical to the syphilis bug, but they aren't sexually transmitted.

They are spread by skin contact.

Yes.

Usually in children living in tropical areas with poor sanitation.

First up, we have yaws.

That's treponema pallidum subspecies pertinu.

But the mnemonic is all about the sound.

Yaws sounds like jaws.

And the cartoon shows a man literally being bitten in the face by sharks.

It's aggressive imagery, but it works.

Jaws implies destruction.

Yaws starts as a skin infection, but can progress to destroy bone and cartilage.

It can cause severe facial disfigurement.

The sharks biting the face represent that destructive nature of the disease on the skin and bone structure.

So if you hear yaws, think jaws, think destruction.

Right.

And then we have the artistic cousin, Pinta.

This is treponema pallidum subspecies carretium.

The cartoon here shows a man looking terrified as he's being splashed with red and blue paint.

And he's yelling in Spanish.

He is.

The speech bubble says,

which means please don't paint the face.

I assume Pinta translates to paint.

Yes.

Pinta is Spanish for paint or spot.

This disease is strictly dermatologic.

It doesn't eat the bone like yaws.

It doesn't attack the heart like syphilis.

It only affects the skin.

And the paint splashes.

What's that about?

They represent the symptom.

Pinta causes hypopigmented, which is light, or hyperpigmented, which is dark, patches of discoloration on the skin, red, blue, white.

It looks like the person has been splashed with paint.

So yaws is sharks for bone destruction.

Pinta is paint for skin discoloration.

And remember, neither is an STI.

They are contact infections.

There's a third one mentioned briefly called Behel, which is similar to yaws, but in arid climates.

But yaws and Pinta are the ones with the big cartoons.

Okay.

We are leaving the land of treponema.

Let's pack our bags and move to the next big genus in the Spear Shed family.

Borrelia.

Borrelia.

And this brings us to a disease that is very relevant right now, especially if you live in the Northeast United States or Europe.

Lime disease.

The bug is Borrelia burgdorferi.

And the mnemonic here relies on a simple pun that I appreciate.

The lime.

L -I -M -E becomes L -I -M -E.

Image 8 shows literal limes.

But they aren't just sitting there.

They're being squeezed.

In the first panel, there are green lime slices dripping juice onto a plate, and the juice forms a very specific pattern.

It forms a bullseye.

A red ring with a clear center.

This represents the classic rash of stage one lime disease.

Correct.

We call it erythema migrans.

It's a rash that starts at the site of the tick bite, specifically the exodes tick.

The bacteria migrate outward through the skin, creating that expanding ring.

The lime juice dripping creates the bullseye.

That's stage one.

Early localized.

But then the cartoon goes absolutely chaotic.

We move to Image 9, which is stage two.

Early disseminated.

The lime is no longer just dripping.

It is shooting lightning bolts.

This signifies that the bacteria are spreading, disseminating through the blood to other organs.

The lightning bolts are hitting three specific targets in the cartoon, and these constitute the classic triad of disseminated lime.

Target number one.

The brain and face.

Right.

This represents the neurological involvement.

In early disseminated lime, you can get aseptic meningitis.

But the classic presentation, the one the boards love, is Bell's palsy.

That's facial paralysis.

Yes.

And typically with lime, it can be bilateral Bell's palsy, meaning both sides of the face are paralyzed.

Both sides.

Yes.

That is very rare in other conditions.

If you see bilateral facial droop, you have to think lime.

Okay, that's a good tip.

Target number two.

The heart.

The lightning bolt is going straight through a heart.

This represents Lyme Carditis.

Specifically, the bacteria interfere with the electrical signals of the heart, causing heart block.

So the heart beats too slowly.

Exactly.

Too slowly or it skips beats.

It can be fatal if untreated, but often it resolves with antibiotics.

And target number three.

The knee.

The joints.

Migratory joint pain and arthritis are hallmarks of Lyme disease.

It often affects the large joints like the knees.

This can sometimes persist into stage three, becoming chronic.

So if you remember the Lyme shooting lightning, you remember the triad,

brain, which is Bell's palsy, heart, which is block, and knee, which is arthritis.

Exactly.

It connects the dermatological sign, the bullseye, with the systemic targets.

Now, Borrelia burgdorferi isn't the only Borrelia mentioned.

There's a cousin called Borrelia recurrentis.

Right.

This causes relapsing fever and the name tells you the symptom.

You get a fever, it goes away, it comes back, it goes away.

Why does it do that?

We talked about the syphilis relapse loop, but this seems different.

Why doesn't the body just fight it off once and for all?

The chapter explains this with the concept of antigenic variation.

Okay.

This is a fascinating mechanism.

Think of the bacteria as a bank robber wearing a specific mask.

Okay, I'm picturing it.

A robber in a mask.

The police, your antibodies, study the security footage.

They learn to recognize that mask.

They swarm in and start arresting or killing everyone wearing that mask.

So the fever breaks, the patient feels better.

Exactly.

The police are winning, but a few of the bank robbers are hiding in the back room

and they have a wardrobe change.

They take off the old mask and put on a completely new one, new surface antigens.

So when they come back out.

The police don't recognize them.

The old antibodies are useless against the new mask.

The bacteria multiply unchecked.

The fever spikes again.

That's the relapse.

And then the police have to learn a new mask.

Yes.

They learn the new mask, kill those bacteria, the fever drops, but then the survivors put on a third mask.

This cycle repeats until the bacteria runs out of disguises or the body finally corners them all.

That is incredibly sneaky.

Yeah.

So Beryllia recurrentis is the master of disguise.

It is.

That's the mechanism of the relapse.

All right.

We have covered Trebinema and Beryllia.

We have one final member of the Spirachet family to meet.

The visual for this one is image 10.

And honestly, it's my favorite because it's just so absurd.

It is pretty great.

It is.

It's a little spiral organism.

Surfing.

Yes, the surfer.

He's shaped like a question mark.

He's got little sunglasses on and he's surfing on.

I guess it's supposed to be water.

It represents water.

Yes.

But let's break down the details.

First, the shape.

The organism is leptospira interrogan.

Interrogans, like an interrogation.

Like an interrogation mark or a question mark.

Under the microscope, leptospira is a spiral that has a hook on one or both ends, making it look exactly like a question mark.

So the name literally describes the shape.

Hence, the surfer is question mark shaped.

Exactly.

And the surfing, that reminds us of the transmission.

Which is water.

Specifically, water that has been contaminated with animal urine.

Gross.

It is.

Rodents, dogs, livestock, they shed the bacteria in their urine.

If that gets into a pond or floodwaters and you go swimming with a cut on your legs.

So you're surfing in animal pee water.

Unfortunately, yes.

That's how you get it.

It's common in triathletes swimming in lakes or people caught in floods.

And in the cartoon, as he's surfing down, there are these little Y shapes attacking him.

What are those?

Those Y shapes are the universal symbol for antibodies.

It shows the immune system attacking the organism.

This is important because leptospirosis is a biphasic illness.

Two phases.

Yep.

First phase is the flu -like illness when the bacteria are in the blood.

Then you get better.

Then the antibodies attack, which are the Y shapes, and you get the second immune -mediated phase.

This is often called Wiles' disease.

What happens in Wiles' disease?

It's serious.

It involves kidney failure, azotemia liver damage, which causes jaundice and hemorrhage.

So surfer equals water and urine.

Question mark equals leptospira interagans.

And the Y shapes equal immune attack, causing kidney and liver failure.

Simple as that.

The cartoon gives you everything you need.

We have unpacked a massive amount of biology here.

I feel my brain is full of cartoons.

That's a good thing.

Let's do a quick lightning round recap to make sure these hooks are set.

I'll say the bug.

You give me the hook.

Let's do it.

Treponema pallidum.

Syphilis.

Think of the timeline.

Primary is the painless chancre, which is the trap.

Secondary is the moonway.

Systemic spread to palms and soles.

Latent fall is the rule of thirds.

Tertiary is gummy bears for gummas, tree bark aorta, and the slapping gait for neural syphilis.

Non -venereal turpinemas.

Yaws is jaws.

Think sharks and bone destruction.

Pinta is paint.

Think skin color changes.

Borrelia burgdorferi.

Lime.

Think limes.

Squeezing the juice creates the bullseye rash.

Then the lightning bolts strike the head for Bell's palsy, the heart for heart block, and the knees for arthritis.

Borrelia recurrentis.

Relapsing fever.

The bank robber changing masks.

That's antigenic variation.

And finally, leptospora.

The question mark surfer in the urine -contaminated water.

And beware the Y antibodies that cause Wiles' disease.

It really does sound ridiculous when you say it all out loud like that.

It does, but that's the point.

I mean, in the middle of a stressful exam or a busy shift at 3am, you might blank on the Latin name or the textbook definition.

Yeah, of course.

But you will remember a moon saying,

or a lime shooting lightning.

Absolutely.

These visuals are mental hooks.

They let you hang the complex data on something sturdy and memorable.

And that's what understanding clinical microbiology is about.

It's not just lists.

It's stories and patterns.

Well, I think we have successfully navigated spiral waters of the Spirachates.

I'm going to be seeing gummy bears very differently from now on.

Sorry about that.

It's worth it for the knowledge.

Thank you for walking us through this.

It was incredibly helpful.

My pleasure.

It was fun.

And thank you to everyone listening to this deep dive into Chapter 14.

We hope this makes your study session a little less painful and a lot more colorful.

Keep visualizing.

Keep looking for those patterns.

This is the Last Minute Lecture Team signing off.

Until next time.