Chapter 29: Rest of the RNA Viruses

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're doing something a little different.

Usually, we tackle a specific topic, a single event, a new technology or, you know, a specific historical figure.

But today, we are tackling a feeling.

A feeling.

A very specific feeling that I think every student,

every lifelong learner, and honestly, anyone who has ever stared at a massive textbook in despair knows all too well.

That feeling of being like 90 % done, but you just hit a wall.

Exactly.

Yeah.

We're tackling the leftovers.

We're looking at Chapter 29 of Clinical Microbiology made ridiculously simple.

Oh, I know this one.

The title of the chapter is literally the rest of the RNA viruses.

And let's be honest, when you get to Chapter 29 in a microbiology textbook, you're usually just trying to survive.

Yeah, you're on fumes.

You've done the big famous bacteria, you've memorized the herpes viruses, you survived the flu, and then you hit this junk drawer.

It does feel like a junk drawer, doesn't it?

The rest.

It sounds so dismissive, but that is a dangerous, dangerous assumption to make.

How so?

Because if you treat Chapter 29 like a junk drawer, you are missing some of the most deadly, the most explosive,

and the most clinically relevant pathogens on the planet.

That is the hook right there.

We aren't just reading a list of the B team viruses.

We are talking about rabies.

We are talking about Ebola.

We are talking about the virus family that shut down the world for a few years, COVID -19.

They are all hiding in this miscellaneous chapter.

Right.

And the challenge, and really the mission of this deep dive, is that because they are the rest, they don't have a single unifying structure.

It's a grab bag.

Yeah, it's just a list.

You have viruses that cause colds sitting right next to viruses that cause your brain to swell.

So memorizing them is a nightmare, unless you have a strategy.

And luckily, our source material today is famous for its strategy.

It is.

We aren't just reading lists.

We are going to walk through the visual mnemonics, the cartoons that this book uses to,

you know, force these viruses into your brain.

You've got a giant lumberjack, right?

A giant lumberjack, a screaming roller coaster, a drunk rhinoceros, and a cat using a litter box.

It sounds ridiculous, hence the title of the book, but these images are actually sophisticated memory palaces.

They turn abstract names into concrete locations.

So if you can visualize the cartoon.

You can diagnose the patient.

It's that direct.

So here's the plan.

We're going to go image by image.

We're going to decode the arbovirus forest, survive the alpha virus roller coaster, visit the Picorna Verde zoo, and end with the hemorrhagic fevers.

It's a whole tour.

If you are a med student, this is high yield gold.

If you're just curious, get ready to learn why a Paul Bunyan costume helps doctors diagnose brain swelling.

I can't wait.

Let's get into the forest.

Okay, let's unpack this first scene.

We are looking at a cartoon of a giant lumberjack.

This is Paul Bunyan.

An American folklore classic.

Giant axe, blue ox, the whole deal.

Except in this textbook,

he is dressed, well, oddly.

He isn't wearing his flannel.

He's wearing a toga.

A toga.

Okay.

And he is standing next to a tree and there is a giant mosquito biting him right on the forehead.

Okay, so let's pause and decode this because this one image is doing a lot of heavy lifting.

It represents the arboviruses.

Arboviruses.

Now, an important distinction here right off the bat.

Arbovirus is not a taxonomic family.

You won't find arboviridae in a genetic sequencing chart.

Wait, really?

I feel like I hear that term all the time in medical dramas.

It's an arbovirus.

You do.

But arbovirus describes a mode of transmission, not a genetic lineage.

A mode of transmission.

It stands for arthropod borne virus.

Oh, arthropod borne.

That's why the word ARBO is written vertically on the tree trunk in the cartoon.

It's the arbo tree.

Oh, I see what they did there.

Arbo tree.

Okay, so this groups together any virus that uses a bug, usually a mosquito or a tick to get around.

Exactly.

It's an ecological term.

It tells you about the virus's lifestyle.

It needs an arthropod vector to get from host to host.

And that's the mosquito biting Paul Bunyan.

That's the unifying theme.

But within this lifestyle of being bug borne, we have three distinct genetic families represented in this one drawing.

So the drawing is a map of three different families that just happen to use the same transportation system.

That's a great way to put it.

Let's break them down.

First, we have Paul Bunyan himself.

Paul Bunyan represents the bunyaviridae.

That one is pretty straightforward.

Bunyan for bunyaviridae.

Got it.

Then we have his fashion choice, the toga.

Right, the toga represents the togaviridae.

This is a major family that includes some nasty players we'll see later.

Okay, toga for togaviridae.

So just link Paul Bunyan in a toga to bunyaviridae and togaviridae.

And the third one, the mosquito is actually talking in the cartoon.

He is.

It's biting his forehead and saying,

great flavor.

Flavor.

That is your trigger for flevaviridae.

Flevaviridae.

Okay, that sticks.

Wow.

So just by picturing a lumberjack in a toga getting bitten by a tasty mosquito, we've locked in bunyaviridae, togaviridae, and flevaviridae.

Precisely.

It organizes the filing cabinet in your brain.

That's incredible.

Now, we need to zoom in on a couple of specific members of these families that the text highlights because simply knowing the family names isn't enough for bunyaviridae Paul Bunyan.

The text specifically calls out hantavirus.

Hantavirus pulmonary syndrome.

I remember hearing about this.

Usually involves camping or cleaning out old sheds, right?

Yes.

Now here is where it gets interesting and a little tricky.

Okay.

Hantavirus is a bunyavirus, so it's in the Paul Bunyan family genetically,

but strictly speaking, it's not an arbovirus.

Oh, Paul Bunyan's mosquito isn't involved.

Not for hantavirus.

It's the exception that proves the rule.

So how is it spread?

Hantavirus is spread by rodent droppings, deer mice specifically.

You sweep up a cabin that's been closed for the winter.

You kick up dust containing dried urine or feces.

You inhale it and you get infected.

No mosquito required.

No mosquito required.

So why is it in the arbovirus picture?

Because genetics wins.

It belongs to the bunyaviridae family, so it lives in this part of the mental map, even if the transmission is slightly different.

So it's a family member with a hantavirus pulmonary syndrome right there next to bunyaviridae to make sure you don't forget it.

It's like the cousin who lives in the same house but takes a different bus to work.

Okay.

Noted.

Rodent droppings for hantavirus, but it's still part of the bunyan clan.

Now what about the flaviridae, the flavor viruses?

The big one mentioned here is West Nile virus.

Right.

And looking at the source material, West Nile gets a lot of real estate.

There are sections for clinical manifestations,

diagnosis, prevention that usually signals exam bait or just clinically critical.

Absolutely.

West Nile is the classic arbovirus in North America.

It's a fly virus.

The cycle is fascinating.

It usually bounces between birds and mosquitoes.

And humans.

Humans are what we call dead end hosts.

Meaning we get sick, but we don't pass it on.

Right.

The virus doesn't replicate high enough in our blood for another mosquito to pick it up from us, but while it's in us, it can cause havoc.

Havoc how?

Most people have no symptoms, maybe a summer flu, but for some, especially older adults, it causes meningitis or encephalitis.

Swelling of the brain.

Swelling of the brain.

And that's why understanding this arbovirus grouping is so important.

How so?

When a patient comes in with fever, confusion, and a stiff neck in August, you have to think about the mosquito bite they got two weeks ago.

But if it's January?

If they come in with the same symptoms in January, you can probably rule out West Nile.

The arbo part, the seasonality of the mosquito is a diagnostic clue.

So Paul Bunyan isn't just a funny drawing.

He's a diagnostic checklist for a summer fever.

That is the power of the mnemonic.

All right.

Let's leave the forest and go to the theme park.

We are staying within the families we just learned, but drilling down.

The next visual is the alpha virus roller coaster.

This is a subsection of the toga viridae.

Remember the toga?

Right, Paul Bunyan's toga.

Well, within that family, we have a genus called the alphaviruses.

And the cartoon shows a roller coaster loop.

There are people in the car and they look terrified.

They're screaming.

And the speech bubbles are very specific.

Why are they screaming?

One says we, one says E, and one says V.

I love this one because it's auditory.

You can hear the screaming in your head.

We, E, V, V.

Right.

These are acronyms for the three major mosquito -borne encephalotides found in the Americas.

Okay.

What do they stand for?

Western Equine Encephalitis.

We, E, E.

Eastern Equine Encephalitis, E.

And Venezuelan Equine Encephalitis, V, E.

We, E, and V.

Western Eastern Venezuelan.

And they are on a roller coaster because alpha.

Yeah.

Or just because they're intense.

Probably because roller coasters are intense, like these diseases.

But notice the name equine.

Equine, like horses.

These are diseases that affect horses too.

Often you'll see an outbreak in horses in a region before you start seeing human cases.

So the canary in the coal mine is a horse in this case.

Exactly.

Now look closely at the writers in the cartoon.

Okay.

What's one of them doing?

One of them is clutching their head and shouting, I have a headache.

Yeah, that seems like a bad time to be on a roller coaster.

But I assume this isn't just motion sickness.

It's a clinical clue.

Encephalitis literally means inflammation of the brain.

The Hallmark symptom is a severe headache, often with fever and altered mental status.

The cartoon uses the headache on the roller coaster to remind you that these alpha viruses target the central nervous system.

So it distinguishes them from other viruses that might just cause a rash or a fever.

Exactly.

These guys go for the brain.

And there's a mosquito emblem on the front of the roller coaster car just to one outlier in the toga viridae family that is not on the roller coaster.

Oh, I see that in the text list.

Ruby virus.

Right.

Rubivirus causes rubella, also known as German measles.

Okay.

It is genetically a toga virus.

It belongs to the family, but it is not an arbovirus.

No mosquitoes.

No mosquitoes.

It's respiratory.

You catch it from a cough or sneeze.

Right.

That's the R in the MMR.

Yeah, the very same.

And it causes a rash and fever and it's devastating for pregnant women.

But because it doesn't use mosquitoes and doesn't typically cause encephalitis, it's not on the roller coaster ride.

It's in the toga family album, but it's sitting this trip out.

Perfect way to put it.

Got it.

So toga viridae splits, you've got the mosquito -borne roller coaster crew causing headaches.

And then you've got rubella over in the corner doing its own respiratory thing.

Perfect summary.

That distinction is a favorite topic for examiners.

Okay.

Let's move on.

We are leaving the bugs behind and entering the zoo.

This next family is massive.

The picorna viridae.

Picorna viridae.

The name itself is a mnemonic, if you know a little etymology.

Yeah.

Pico means very small.

RNA is the genetic material.

So small RNA viruses.

But despite being small, this family is huge in terms of members.

The list in the source text is long.

Entrovirus, poliovirus, coxsacky A and B, echoviruses, and rhinovirus.

Feels like crowded house.

It is.

They're often grouped as enteroviruses, meaning they replicate in the gut or entero.

Except for rhinovirus.

Except for rhinovirus, which prefers the nose, but they share a similar structure.

Let's talk about polio first.

It's the most famous one here.

Absolutely.

The text highlights the disease polio.

It mentions vaccines,

positives,

and negatives.

It's a bit cryptic in the outline, but what should we take away from this?

Polio is the grandfather of this room.

It's an enterovirus.

It enters through the mouth fecal oral transmission and replicates in the gut.

Now, the key takeaway for any student here is the vaccine story because it teaches us about immunology.

Right.

The text mentions live vaccines versus inactivated.

This is the Salk versus Sabin debate.

Right.

Exactly.

The Sabin oral vaccine that drops on the sugar cube is a live, weakened virus.

Live, okay.

Because it's live and you swallow it, it infects the gut just like the virus.

This creates amazing mucosal immunity.

It stops the virus from even setting up shock in your intestines.

But there's a catch, I assume.

The catch is that because it's a live virus, in very rare cases, we're talking one in millions,

it can mutate back to a virulent form and actually cause polio.

That's a negative.

Wow.

And the other option?

The inactivated vaccine, the Salk shot, it's a dead virus.

So no risk.

Zero risk of causing disease.

That's a positive.

But it produces antibodies in the blood, not the gut.

What's the downside of that?

So you might still get infected in your gut and shed the virus in your stool, even if you don't get paralyzed yourself.

You're protected, but you could still be a carrier.

So when the source says positives and negatives, it's referring to that trade off between safety and community immunity.

Exactly.

And also the most polio infections, like 90 to 95%, are asymptomatic.

That's a positive.

Right.

But a small percentage attack the nerves and cause paralysis.

That's the devastating negative.

It's a game of odds.

And then we have these other names, Cocksacky and Echo.

They sound like a law firm or a buddy cop movie.

Cocksacky, Echo, and the newer enteroviruses like D68.

These are the cousins of polio.

They are incredibly common.

I feel like I hear Cocksacky every time a friend's kid is sick.

You do.

If you hear about hand, foot, and mouth disease in a daycare blisters on the palms and soles, that's Cocksacky A.

If you hear about viral meningitis in a teenager, a severe headache, but they recover fully, it's often an echovirus or Cocksacky B.

And Cocksacky B is more serious.

It can be.

It can also attack the heart, causing myocarditis.

So picornaviridae is basically these stuff kids catch family.

In many ways, yes.

From the sniffles to meningitis to paralysis, this family covers the spectrum of childhood viral illness.

Speaking of sniffles, that brings us to our next major segment.

We are looking at the respiratory viruses.

And the visual here is, well, it's a mood.

It is a mood.

It's one of the best drawings in the book.

It is a rhinoceros, a blue rhinoceros.

He looks miserable.

He has a runny nose, tears in his eyes, and he is double -fisting.

Double -fisting.

In one hand or hoof, he has a bottle of Nyquil.

In the other, he has a bottle of Corona beer.

This is one of the most effective mnemonics in the book because it links the mundane with the deadly.

How so?

It connects the common cold to the global pandemic.

Let's start with the rhino.

The rhino represents rhinovirus.

Rhino means nose.

This is the primary cause of the common cold.

That's why he has the Nyquil.

He's congested.

Simple enough.

Rhino equals runny nose equals common cold.

But why is he holding a Corona beer?

This links rhinovirus to coronaviruses.

Historically, before 2002, coronaviruses were just seen as another cause of the common cold.

Oh, really?

Yeah.

They were the second most common cause after rhinovirus.

The rhino holding the Corona tells you these two go together.

They both cause colds.

But we know that story changed.

We know that story changed very dramatically.

It did.

And the source text reflects that change with a shift in font color.

We have viruses that cause the cold in one section, and then in red, scary text, the deadly coronaviruses.

Yeah.

Let's get serious fast.

SARS -CoV, MERS -CoV, and SARS -CoV -2.

This is a crucial pivot point in microbiology history.

We used to think of this family as a nuisance.

Then came SARS,

severe acute respiratory syndrome, in 2003.

Then MERS.

Then MERS, Middle East respiratory syndrome in 2012, and obviously COVID -19.

What's fascinating is that the book keeps them anchored to this common cold image.

It's like, remember they started as just a cold virus.

And biologically, that's vital to understand because even the deadly ones often start with those same upper respiratory symptoms.

The runny nose, the cough before descending into the lungs to cause the severe pneumonia.

So the rhino with the beer reminds you of the shared lineage.

They are cousins.

One is annoying.

The other is lethal.

So if you see Corona on an exam, don't just think pandemic.

Think respiratory virus ranges from sniffles to death.

Exactly.

And don't forget MERS.

It's often the forgotten middle child, but it has a very high mortality rate.

It's linked to camels in the east.

It's still out there.

Okay.

Let's switch gears.

We've done the head with encephalitis, the nose and lungs with respiratory.

Now we are moving down the GI track.

We are talking about diarrhea, the glamorous side of microbiology.

This is where things get messy.

And the mascot for this is a cat, specifically a calico cat, a calico cat using a litter box.

The visual is pretty explicit.

The cat is doing its business and there is steam rising from the litter box.

Yeah, it's gross.

But I guess that helps memory.

It does.

The more visceral, the better for retention.

So decode the cat for us.

Calico cat stands for caliceviridae.

This is the family name.

Okay.

The fact that it's using a litter box tells you the primary clinical presentation,

gastrointestinal illness,

diarrhea and vomiting.

But there's some geography on this cat too.

There's an arrow on a wall map pointing to Norway.

Norway is the trigger for Norwalk virus, which we now commonly call norovirus.

Ah, the cruise ship virus.

The very same.

Norovirus is the king of viral gastroenteritis in adults.

It's incredibly contagious.

How contagious.

It takes very few viral particles to make you sick and it's hard to kill with standard cleaners.

That's why it rips through closed environments like cruise ships, nursing homes and schools.

So calico cat in Norway links caliceviridae to Norwalk or norovirus.

Correct.

There's one detail in this cartoon.

The arrow pointing to Norway isn't straight.

It's curving around the cat.

It's rotating.

Rotate.

That is your clue for rotovirus.

Okay.

So rotovirus is lumped in here visually.

Right.

Now, scientifically, rotovirus is actually a real virus family member, not caliceviridae.

They have different structures.

But clinically, they're similar.

Clinically, they are the big two for viral diarrhea.

The mnemonic groups them by symptom rather than strict genetics here.

The rotating arrow around the dirty litter box links rotovirus to the same clinical picture.

So calico cat equals caliceviridae norwalk.

Rotating arrow equals rotovirus.

Result equals stay near a bathroom.

That's about right.

Is there a way to tell them apart clinically?

For a student, the distinction is usually demographic.

Rotovirus is historically the major killer of infants and young children worldwide due to dehydration.

And we have a vaccine for it now.

We do, which has helped immensely.

Norovirus is the winter vomiting bug that affects everyone, adults and kids alike.

Got it.

Kids versus cruise ships.

But both are represented by the messy cat.

It's a messy business, but a very common one.

All right, we are getting to the heavy hitters now.

We've had some scary ones, but this next image is pure aggression.

We are talking about rabies.

Rabies is in a league at its own.

It has virtually 100 % mortality if symptoms appear.

100%.

That is a statistic that is hard to wrap your head around.

Once the clinical disease starts, there's almost no stopping it.

The cartoon is intense.

It's a mad dog.

It's foaming at the mouth and it is holding a gun.

A dog with a gun.

It sounds like a bad B movie.

And it's shooting a bullet, but the bullet isn't a piece of lead.

It looks like a virus particle.

This is a classic morphology clue.

The virus that causes rabies, which belongs to the Rabdoviridae family,

is physically shaped like a bullet.

Like a bullet.

Flat on one end, rounded on the other.

If you look at it under an electron microscope, it looks exactly like a bullet.

So Rabdo equals rabies equals bullet shaped.

That's easy.

The image goes deeper into the pathogenesis, the way the disease progresses.

This is the most critical part for a doctor to understand.

What's it show?

You see the bullet biting or hitting a human hand.

Then there is an arrow tracing a path from the hand up the arm all the way to the brain.

And there's a clock next to it that says weeks one year.

This illustrates the unique feature of rabies.

Most viruses you get bit, the virus enters the blood, viremia, and you get sick in a few days.

Rabies doesn't really do that.

What does it do?

It binds to the nerve endings at the site of the bite and then it travels retrograde backward along the nerve axons.

It crawls up the nerves to the spinal cord and then to the brain.

It's literally climbing a ladder to your brain.

Exactly.

And because it's crawling physically up the nerve fibers rather than flying through the blood, it takes time.

Weeks to a year.

That travel time takes weeks, sometimes months or even a year, depending on how far the bite is from the brain.

A bite on the toe takes longer to reach the brain than a bite on the face.

And that delay is the only reason we can save people, right?

Exactly.

This is the key medical takeaway.

If it happened instantly, we'd be helpless.

But because of that clock in the cartoon, we have a window of time.

So what's the treatment?

If we give the vaccine and antibodies, the IEG, after the bite but before the virus reaches the brain, the immune system can intercept it.

We are racing the virus up the arm.

That is incredibly dramatic.

It really is a race against time.

It is.

There's one more inset image in this panel.

It shows a close -up of a cell with a dark blob inside it labeled negri body.

What is that?

This is the pathology board question.

If you look at the brain cells of an animal or person who died of rabies under a microscope, you see these dark e -synophilic inclusions in the cytoplasm.

And those are negri bodies.

They are called negri bodies.

They are basically factories where the virus is replicating.

If you see negri body on a test, the answer is rabies.

Period.

So the mad dog gives us bullet

travel, long incubation, and negri bodies.

That's pretty much everything you need to know to diagnose and understand the urgency of rabies.

Okay, we have reached the final segment.

And the outline calls this the hemorrhagic fevers.

The bleeders.

The source material is a bit sparse here.

There are blank tables for clinical findings and treatment.

Which is chillingly accurate in a way.

For a long time, there wasn't much treatment other than supportive care keeping the patient hydrated and hoping their immune system won the fight.

The text lists two main families here.

First, the phylloviridae.

Phylloviridae.

Phyllo means thread -like.

Thread -like.

If you look at Ebola or Marburg virus under a microscope, they don't look like little balls or bullets.

They look like long twisted threads or sometimes a shepherd's crook.

And the members listed are Ebola and Marburg.

These are the ones that make the headlines.

They cause severe hemorrhagic fever.

High fever, vascular leaking, bleeding from mucous membranes.

They're terrifyingly infectious via body fluids.

Right.

And the second family listed is orenoviridae.

Orenoviridae.

Arena comes from the Latin for sand, like an arena floor.

Sand.

Exactly.

Under the microscope, these viruses look grainy, like they have sand inside them.

Why do they look sandy?

That sand is actually host ribosomes, the little protein factories that the virus stole from the cell it

packs them up and carries them along.

It's a thief.

It is.

But for the purpose of this deep dive, just know that orenoviruses, like Lassa fever, are the other major category of viral hemorrhagic fevers alongside the follow viruses.

So we have the threads,

phyllo Ebola, and the sand arena.

Both cause hemorrhagic fever and both are things you definitely do not want to encounter without a hazmat suit.

Absolutely.

The source groups them simply to say these are the RNA viruses that cause you to bleed out.

It's a blunt classification, but a necessary one.

It creates a danger box in your mind.

If you see thread or sand, think hemorrhage.

Wow.

We have covered a lot of ground from a lumberjack to a roller coaster to a mad dog.

It really is a junk drawer of terrifying things.

It is.

But hopefully it's not a junk drawer in your mind anymore.

It's a map.

It's an organized map.

The images give structure to the chaos.

Let's do a rapid fire recap to prove it.

I'm going to throw the image at you.

You give me the medical takeaway.

Ready?

Ready.

Paul Bunyan in a toga.

Arboviruses, Bunya viridae, so hantavirus, vir, rodents, toga viridae, and flaviviridae, which is West Nile via mosquitoes.

Screaming on a roller coaster, we -e -e -v -e.

Toga viridae again, but specifically the alpha viruses.

Equine encephalitis and the headache means brain swelling.

Rhino with a beer.

Rhinovirus for the common cold linked to coronavirus, which is the common cold, plus the deadly SARS, MERS, and COVID.

Their cousins in respiratory illness.

Calico cat in Norway using a litter box.

Caliceviridae, so Norwalk norovirus, and rotavirus, that's the visual for viral diarrhea.

Dog with a gun.

Rabies from the Robdovirus family.

Bullet -shaped virus.

Travels up nerves.

Negri bodies.

The clock is ticking.

And finally, threads and sand.

Filiviridae, which is Ebola,

and

Chapter 29 sounds like the boring end of the book, but this might be the most memorable chapter of them all.

It's the power of visual learning.

In a high -pressure situation, whether it's a board exam or a 3 a .m.

shift in the ER,

your brain might not recall a black and white text list.

But it will recall a drunk rhino.

But it will recall a drunk rhino.

And that silly image might just prompt you to order the right respiratory panel.

Or the Paul Bunyan image.

I remind you to ask about mosquito bites when a patient is confused.

These ridiculous associations are actually lifelines.

They connect the dots between the abstract biology and the patient in front of you.

That's why we love this book.

Well, there you have it.

The leftovers, unpacked.

Chapter 29 isn't a junk drawer.

It's a gallery of rogues.

A very dangerous gallery.

Thanks for joining us on this deep dive into the rest of the RNA viruses.

Go draw a picture of a lumberjack.

It might save a life someday.

We'll see you next time.

Stay curious and wash your hands.