Chapter 21: Microbial Diseases of the Skin and Eyes

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Welcome to the Deep Dive.

Today we're taking a shortcut to becoming really well informed about and let's be honest, often take for granted,

our skin and eyes.

You might think of them as just outer coverings, but they are incredibly complex battlegrounds, constantly fighting off microscopic invaders.

That's absolutely right.

Our mission today is to unpack a chapter from microbiology and introduction, focusing specifically on how microbes interact with our skin and eyes.

It's fascinating stuff.

From normal residents to, well, serious pathogens.

Exactly.

We'll explore their structures, the diseases they cause, how they're transmitted and, you know, real world applications of all this knowledge.

So what does this all mean for you listening?

Well, you're about to get a captivating look at the unseen world right there on your own body.

Yeah, you'll gain insights into common ailments, maybe things you've experienced yourself and understand why certain public health measures are, well, just so crucial.

Let's unpack this chapter.

Let's do it.

Okay, let's start with the basics then, our skin.

It's this remarkable physical barrier, right?

Almost impossible for pathogens to penetrate when it's intact.

Right, when it's intact.

That's the key.

But there are a few surprising ways microbes can get in.

Like what?

Well, through tiny breaks, you know, cuts or scrapes, or even believe it or not, larval forms of some parasites can actually burrow through.

Wow.

Okay.

What's also fascinating is just how inhospitable the skin generally is for most

microorganisms.

How so?

Well, its secretions are acidic and most areas are pretty dry, which isn't great for bacterial growth.

Makes sense.

Dry and acidic sounds tough.

It is.

However, you do have some moist regions, like say the armpit or between the legs.

Those can support pretty large bacterial populations.

And even the scalp, which might seem dry, has its own little community thriving there.

And you mentioned secretions.

So it's not just a physical wall, it's a chemical one too.

Precisely.

Think about perspiration, sweat.

It provides moisture and nutrients.

Yeah, but it also contains salt.

Which would inhibit a lot of microbes, right?

Exactly.

Plus, sweat contains an enzyme called lysozyme.

It actually breaks down bacterial cell walls and antimicrobial peptides to tiny natural antibiotics.

Okay, wow.

That's quite a cocktail.

What about oil?

Yeah, sebum from our oil glands.

It's a mix of lipids, proteins, salts, keeps skin and hair from drying out.

And does it fight microbes too?

It does.

Fatty acids in sebum inhibit certain pathogens, but sebum itself can also be a nutrient source for other microbes.

So it's a bit of a double -edged sword.

So, okay, despite all these impressive defenses, the physical barrier, the chemicals,

where are the weak points?

Where do things get in?

Good question.

It often comes down to anatomy.

The hair follicles, the sweat gland ducts, oil gland ducts, they extend down into the dermis.

They're like tiny tunnels.

Pretty much.

They provide passageways for microorganisms to enter and potentially penetrate deeper tissues.

Understanding that is really key to understanding how a lot of skin infections start.

Got it.

And beyond the skin itself, we have mucus membranes, right?

Lining our respiratory tract, digestive tract.

Exactly.

Lining body cavities that open to the exterior.

They're another huge line of defense.

How do they work?

Well, they consist of tightly packed epithelial cells.

Many of these secrete mucus.

Sticky stuff.

Yeah, it's designed to trap particles, including microorganisms.

And in the respiratory system, you have cilia tiny hairs that sweep this trapped material up and out.

Okay.

And chemically?

They're often acidic too, limiting microbial populations.

And like tears in our eyes, they contain that enzyme, lysozyme.

And the surface area is huge, you said.

Vast.

About 400 square meters, if you laid it all out, like a tennis court.

It's an enormous area to protect.

Incredible.

Now, let's talk about the microbes that do live on our skin normally, the normal microbiota.

What makes them special?

How do they survive there?

Well, they're adapted, you see.

They have to be resistant to drying and those high salt concentrations we mentioned.

So specialized residents.

Definitely.

You find a lot of gram -positive -couchy, spherical bacteria that stain purple in a gram test, like staphylocouchy and microcouchy.

And washing doesn't get rid of them completely?

Nope.

Even vigorous washing won't eliminate them.

They just quickly reestablish from places like hair follicles and sweat glands where they're more protected.

I read something about a sort of skin wars.

Are normal microbes actually helping defend us?

That sounds amazing.

It really is.

Take staphylococcus epidermidis.

It's super common on healthy skin, generally non -pathogenic.

Okay.

What it does is it actively enlists our own immune system.

It triggers a specific receptor, a toll -like receptor, on our skin cells.

Triggering an alarm.

Sort of.

It prompts the skin cells to produce something called beta -defensin.

It's an antimicrobial peptide.

Like those ones in sweat.

Similar idea, yeah.

And this beta -defensin inhibits the growth of pathogenic staphylococcus aureus and group A streptococcus.

But here's the cool part.

It doesn't inhibit S epidermidis itself.

Wow.

So it tells our body to attack the bad guys but leave alone, like a friendly bacterial army.

Exactly.

It's a fantastic example of coevolution.

And S epidermidis also ferments glycerol from our skin cells.

Okay.

And produces systemic acid.

This acid actually inhibits cutie bacterium acne.

The acne bacteria.

The very same.

So S epidermidis is fighting acne too, in a way.

This kind of research is actually leading to clinical trials.

For probiotic lotions.

Exactly.

Using these beneficial microbes to treat conditions like eczema.

It's a really exciting area.

That is fascinating.

So we have helpful residents like S epidermidis, but we also have others, like diphtheroids.

Right.

Like cutobacterium acnes.

It's anaerobic, lives deep in hair follicles, feeds on sebum.

And contributes to acne.

Yes.

By producing propionic acid, which helps keep the skin's pH low, but also contributes to inflammation.

And then there's melasecea furfur.

That's a yeast.

Linked to dandruff.

Correct.

It grows on oily secretions, which is why dandruff shampoos often target fungi.

Okay.

Before we dive into specific diseases, maybe we should quickly cover the language doctors use, you know, for skin lesions.

Good idea.

Knowing the terms helps understand diagnoses.

So small fluid -filled lesions.

Those are vesicles.

Like in chickenpox.

Exactly.

If they're bigger, say over a centimeter, they're called bullae.

Flat reddened lesions are macules.

Think measles rash.

Got it.

Raised lesions are papules.

And if those lesions contain pus, they're pustules.

Like in acne.

Vesicles, bullae, macules, papules, pustules.

And there's a term for where the rash is.

Yes.

A skin rash is an axanthin.

If the rash is on mucous membranes, like inside the mouth, it's an ananthin.

Axanthin on skin, ananthin inside.

Useful distinction.

Definitely.

Helps narrow things down quickly.

All right.

Let's get into the bacterial invaders.

Two big names always come up.

Staphylococcus and Streptococcus.

How do we tell them apart and what trouble do they cause?

Visually, under a microscope, Staphylococcus are gram -positive spheres that form irregular clusters.

Think grapes.

Grapes, okay.

Streptococcus are also gram -positive spheres, but they typically grow in chains, like beads on a string.

Grapes versus chains, got it.

And both groups can produce a whole range of invasive enzymes and damaging toxins.

That's how they cause disease.

So for Staphylococcus, which one is the normal resident and which is the main pathogen?

Staphylococcus epidermidis is the common one.

It's coagulus negative, meaning it doesn't clot blood plasma, makes up maybe 90 % of our normal skin microbes.

And it's usually harmless.

Usually.

It really only causes problems when the skin barrier is broken.

Think surgical sites, catheters.

It's great at forming biofilms on medical devices.

Protective slime layers.

Right.

Makes them hard to treat.

Okay, so S.

epidermidis is mostly okay, but Staphylococcus aureus, that's the one we hear about.

That's the major pathogen, yes.

And it's carried by a lot of people.

About 20 % of us have it permanently in our nasal passages.

Wow, 20 % permanently.

And another 60 % carry it occasionally.

It's incredibly hardy, survives for months on surfaces, and it forms those distinctive golden yellow colonies.

Does the color do anything?

Yeah, the pigment seems to protect it from sunlight damage.

And S.

aureus just has a massive arsenal of virulence factors compared to S.

epidermidis.

Like what?

Things that help it invade tissue, toxins that damage cells, ways to evade the immune system.

Almost all pathogenic strains are coagulous positive.

They do clot plasma.

And that clotting helps it.

It's thought to help wall off the infection from immune cells.

It can cause everything from skin infections to life -threatening sepsis.

And it's good at dodging our immune system too.

Incredibly good.

It can block immune cells, kill phagocytes, resist opsonization, that's a tagging for destruction process.

Resist lysozyme too.

It's cell wall is resistant.

It can act as a super antigen, causing the immune system to go haywire.

And frustratingly, getting infected doesn't always give you good immunity against the next time.

So what kind of common infections does S.

aureus cause on the skin?

Well, localized things like folliculitis infected hair follicle, basically, pumples.

Or a stye, an infected eyelash follicle.

More serious is a furuncle, or boil.

That's an abscess inflammation of tissue around a follicle.

Needs draining often because antibiotics don't get in well.

And if it spreads?

If that boil gets really extensive, deep, hard inflammation, usually with a fever, that's a carbuncle.

Much more serious.

And then there's impetigo.

That sounds familiar, very contagious, right?

Especially in kids.

Yes, impetigo.

Mostly caused by S.

aureus, though striptococcus pyogenes can play a role too.

Affects young kids, spreads easily by direct contact.

What does it look like?

Usually starts as small lesions that rupture and form honey -colored crusts.

That's non -bullis impetigo.

Usually heals without scars.

Are there worse forms?

Yes.

Bullis impetigo.

That involves blisters and is actually a localized form of Staphylococcal scalded skin syndrome, or SSS.

Scalded skin.

That sounds bad.

It is.

It's caused by specific exfoliative toxins.

Toxin A causes the bullis impetigo.

Toxin B can circulate systemically.

And cause the full scalded skin syndrome.

Right.

The skin peels off in sheets.

Mostly seen in kids under two.

Looks like a severe burn.

Very serious.

And these toxins, especially the systemic ones, can lead to toxic shock syndrome.

Correct.

Toxic shock syndrome, TSS.

Potentially fatal.

Fever.

Vomiting.

A characteristic sunburn -like rash.

Then shock.

Organ failure.

And it was linked to tampons.

Famously, yes.

Highly absorbent tampons provided the right environment for S.

aureus to produce toxic shock syndrome, toxin 1.

TSS T1, a superantigen.

But non -menstrual TSS happens, too, after surgery or childbirth.

Okay.

Now, our sources had this interesting case study about MRSA in a gym.

Ah, yes.

The college wrestler.

Jason F.

Severe Skin Infection.

Turned out to be MRSA methicillin -resistant S.

aureus.

Meaning standard antibiotics wouldn't work.

Right.

Gram -positive Cochi.

Coagulase -positive.

Sensitivity testing showed it needed vancomycin.

And the investigation pointed to how it spread in the gym.

Exactly.

Wrestling means abrasions.

Skin trauma.

Lots of physical contact.

Shared equipment.

Maybe not clean perfectly.

Classic risk factors.

So the CDC recommendations made sense.

Absolutely.

Clean locker rooms and equipment thoroughly.

And critically, exclude athletes with open -skin lesions from competing until they're healed.

Basic infection control.

Right.

Okay, let's switch to the chains stripped to Cochi.

How do they cause it?

Well, like staph, they secrete toxins and enzymes.

Hemolysins lies red blood cells.

That's important in the lab.

Beta -hemolytic ones are key.

Especially beta -hemolytic group stripped to Cochi,

or GAS.

That's basically streptococcus pyogenes.

A major human pathogen.

Can be deadly.

What makes S.

pyogenes so nasty?

What are its virulence factors?

It's got quite a toolkit.

Streptolysins kill red blood cells and neutrophils.

M protein is a big one.

What does M protein do?

It's on the surface, helps it evade phagocytosis, prevents compliment activation, part of our immune response, makes it slippery to the immune system.

Clever.

Anything else?

A hyaluronic acid capsule.

It resembles human connective tissue, so our immune system doesn't readily recognize it as foreign.

Poorly immunogenic.

Wow.

Camouflage.

Pretty much.

Plus, it produces enzymes like streptotinases to dissolve blood clots, hyaluronidase to break down connective tissue, and deoxyribonucleases to degrade DNA and pus.

All help it spread like wildfire through tissues.

So these are the flesh -eating bacteria we sometimes hear about.

That term is often associated with severe S.

pyogenes infections, yeah.

While most are localized, if they get into deeper tissue, they can be incredibly destructive.

Like erycipolis.

Erycipolis is one example.

Serious infection of the dermal layer.

Reddish patches, often with raised margins, frequently on the face, can lead to sepsis.

Luckily, S.

pyogenes is usually still treatable with penicillin -type antibiotics.

But then there's a really scary one.

Necrotizing fasciitis.

Yeah.

That's the one often called flesh -eating.

It involves rapid, extensive tissue destruction.

Mortality rates can be over 40%.

Why so deadly?

The pyrogenic toxins act as superantigens.

Massive immune overreaction causing damage.

Requires aggressive treatment, broad -spectrum antibiotics, and, crucially, surgical removal of all the dead and infected tissue.

Urgently.

And just like Staph, Strep has its own Toxic Shock Syndrome, too.

It does.

Shreptococcal Toxic Shock Syndrome.

Similar symptoms, but often even more severe than Staphylococcal TSS.

Higher mortality rate, up to 80%.

Wow.

Rash is less common, but bacteria in the bloodstream bacteremia is more likely.

M proteins, shed by the bacteria complex with fibrinogen, bind to neutrophils, causing them to release damaging enzymes.

Leads to shock and organ damage.

A very dangerous complication.

Okay, moving on.

Let's talk about Pseudomonads.

Where do these guys hang out?

Pseudomonads, especially Pseudomonas aeruginosa, are everywhere.

Gram -negative rods, aerobic, found in soil, water.

They can survive in almost any moist environment.

Even soap film.

Yep.

They are incredibly adaptable and notoriously resistant to many antibiotics and disinfectants.

Classic opportunistic pathogens.

So they strike when defenses are down.

Where do we see infections?

A common one is Pseudomonas dermatitis.

Self -limiting rash, often linked to swimming pools, hot tubs, saunas.

Why hot tubs?

The hot, sometimes alkaline water can make chlorine less effective.

And open hair follicles from the heat give the bacteria an entry point.

Also causes otitis externus swimmer's ear.

And they're a problem in hospitals, right?

What makes them so tough there?

Their resistance, plus their ability to form biofilms.

Dense, slimy layers that protect them makes them a huge issue in healthcare settings.

On medical devices.

Exactly.

Catheters, ventilators.

Big problem for cystic fibrosis patients, burn patients.

It's a major opportunistic pathogen.

That blue -green pus you sometimes hear about in burn wounds, that's often aeruginosa producing piosin and pigment.

And didn't one of the clinical cases involve a Pseudomonas outbreak from a pool toy?

Yes.

Perfect example.

Donald and Sharon's rashes.

The source wasn't just the pool water, but p -eruginosa growing in biofilms on pool tiles.

And specifically, a large inflatable toy that never fully dried out.

So even if the water is chlorinated?

Biofilms on surfaces can still harbor the bacteria and cause outbreaks.

Highlights the importance of cleaning those surfaces, too.

So how do we treat these resistant bugs?

It's tough, but newer antibiotics like quinolones and specific anti -pseudomonas, often work.

Silver sulfatizine cream is very useful for burn infections.

Okay.

Another bacterial one mentioned was Beruli ulcer.

Sounds nasty.

It is quite damaging.

Caused by mycobacterium ulcerans, it's an emerging disease, mostly in West and Central Africa, but also other tropical areas.

What does it do?

Progresses slowly, but forms these deep, massive ulcers.

Really disfiguring.

It produces a toxin called mycolactone that causes the tissue destruction.

Where does it come from?

Linked to swamps, slow -flowing water, probably enters through minor skin breaks, or maybe insect bites.

An environmental pathogen, really.

Right.

Now, let's tackle probably the most common skin issue.

Acne.

Definitely not just for teenagers.

Absolutely not.

Affects millions.

Estimated 17 million in the US.

Over 85 % of teens get it.

It starts simple.

Sheds skin cells mixed with sebum, clog, hair follicles.

Forming whiteheads and blackheads.

Exactly.

And the blackhead color, not dirt.

It's oxidized lipids in the sebum plug.

Oh, blocked pores and oil are the root cause.

Pretty much.

And hormones drive sebum production, hence the teenage connection.

Commodonal acne, the mild form with just whiteheads and blackheads, is often treated topically.

But then it gets inflamed.

That's inflammatory acne.

Moderate.

Here, bacteria get involved.

Especially cutobacterium acnes.

Which feeds on sebum.

Right.

It metabolizes glycerol in sebum, produces fatty acids that trigger inflammation, leads to those red bumps, papules, and pus -filled ones, pustules.

How is that treated?

Treatments aimed to reduce sebum, kill C -acnes, or reduce inflammation,

antibiotics, benzoyl peroxide, retinoids, even light therapies.

And the really severe form.

Nodular cystic acne.

Yes.

Nodular cystic acne.

Deep, painful, pus -filled nodules or cysts.

High risk of scarring.

This is where the powerful drug isotretinoin, formerly accutane, comes in.

How does it work?

It dramatically reduces sebum formation.

Very effective.

But it has serious side effects.

The big one being birth defects.

Yes.

It's highly teratogenic, causes severe birth defects if taken during pregnancy, requires extremely strict controls and monitoring for female patients, plus other side effects like dry skin, potential mood changes, powerful drug used carefully.

Okay.

Let's shift to viruses.

So many viral illnesses show up on the skin, don't they?

Even if they start elsewhere.

Absolutely.

The skin is like a billboard for many systemic viral infections.

And as you mentioned, some are mild for most people, but devastating for a fetus.

Let's start with warts.

Pretty common.

Very common.

Benign skin growths caused by papillomaviruses.

Over 50 types.

How do you get them?

Direct contact.

Skin to skin.

Sometimes sexually transmitted.

Warts can show up weeks after infection.

And getting rid of them.

Various ways.

Cryotherapy freezing.

Electrodesication burning.

Acids.

Lasers.

Or prescription drugs like podofilox or amicomod, which boosts the immune response.

But they can be more than just benign growths.

Well, yes.

Certain types of papillomavirus are linked to skin cancers and importantly, cervical cancer.

Genital warts are the most common STI.

So not always harmless in the long run.

Okay.

Now for a major historical disease.

Smallpox.

Absolutely devastating, but conquered.

A true public health triumph.

Smallpox, caused by the variola virus, was a global killer.

Once affected 80 % of Europeans.

Wiped out huge numbers of Native Americans.

Two forms, right?

Major and minor.

Yes.

Variola major had a horrifying 20 -60 % mortality rate.

Variola minor was much milder.

Less than 1%.

How did it spread and manifest?

Respiratory road initially.

Then spread internally.

Then exploded onto the skin with those characteristic pustules.

Everywhere.

And it was eradicated.

How?

The first disease ever eradicated from the human population.

Thanks to a massive global vaccination campaign, led by the WHO.

And the first disease we artificially induced immunity for.

Exactly.

Vaccination started it all.

A key factor was no animal reservoir.

Stop human transmission.

Stop the virus.

Last natural case was in 1977.

Amazing.

But there's still this lingering concern about bioweapons.

Since routine vaccination stopped decades ago.

That's the concern, yes.

US vaccinations stopped in the 70s.

People vaccinated before then have waning immunity, though likely some protection remains.

So we keep vaccine stocks?

Yes.

As a precaution.

And the virus itself is officially kept in only two secure labs worldwide for research.

The vaccine itself isn't without risks, though.

Complications can be treated with specific antivirals or immune globulin.

What about monkeypox, then?

Is it related?

A new threat?

It's related, yes.

An orthopoxvirus, like smallpox.

First found in lab monkeys.

Endemic in small animals in Africa.

And human outbreaks.

Have happened.

One in the US linked to imported pet prairie dogs.

Symptoms resemble smallpox, but usually milder.

Does the smallpox vaccine work?

Yes, it offers protection.

And human -to -human spread has historically been limited, though recent outbreaks have shown that can change.

The WHO monitors it closely.

Okay, let's talk about chickenpox and shingles.

A common childhood illness and its later life sequel.

A classic example of viral latency.

Chickenpox, or varicella, usually mild in kids.

Caused by the herpesvirus varicella virus, also known as HHV3.

Spread how?

Respiratory route.

Leads to that itchy, vesicular rash blisters that then crust over.

Complications like encephalitis or pneumonia are rare, but more common and serious in adults.

And there's that Ray's syndrome connection.

Yes, Ray's syndrome.

A severe complication, mostly in kids and teens recovering from chickenpox or flu.

Vomiting, brain dysfunction, can cause serious neurological damage.

Linked to aspirin.

Strongly linked.

That's why aspirin is generally avoided for kids with fevers or viral illnesses.

Okay, so how do shingles fit in?

Where does the virus go after chickenpox?

It hides.

Like all herpesviruses, HHV3 becomes latent.

It retreats into peripheral nerves and hangs out as viral DNA in the central nerve ganglia.

The immune system can't really get to it there.

For years.

Years.

Decades, even.

Then, often triggered by stress or just aging -related decline in immunity, the virus reactivates.

And that causes shingles.

Exactly.

The reactivated virus travels back down the same nerve pathways to the skin, causes a new outbreak, shingles, or a herpes zoster.

But it looks different from chickenpox.

Yes, because there's some partial immunity.

The vesicles are typically localized along the path of that specific affected nerve, often a band around the waist or on the face, usually just one side of the body.

And it can be very painful.

Extremely.

Severe burning or stabbing pain.

And sometimes that pain, called post -cerpetic neuralgia, persists for months or even years after the rash is gone, debilitating for some people.

Is there treatment or prevention?

Antivirals, like a saclover, can help treat shingles, especially if started early.

For prevention, the chickenpox vaccine, varicella vaccine, introduced in 1995, has drastically cut cases in kids.

And for shingles itself.

There's a newer shingles vaccine, zoster vaccine, recommended for older adults, usually 50 or 60 plus, even if they've had chickenpox or shingles before.

It boosts immunity to prevent reactivation or lessen severity.

Okay.

Another herpes virus.

Herpes zimplex.

Yeah.

HSV.

Cold sores are the common one.

Right.

Two main types.

HSV1 and HSV2.

HSV1, or HSV1, is usually picked up in childhood, often orally or respiratorily.

Super common.

Maybe 90 % of US adults are infected.

And it causes cold sores.

Commonly, yes.

Cold sores or fever blisters.

Painful little vesicles around the lips, usually short -lived.

Why do they keep coming back?

Latency again.

Exactly.

HSV1 becomes latent in the trigeminal nerve ganglia nerves serving the face.

Recurrences triggered by stress, sunlight, UV, hormones.

Can that cause other things?

Yes.

Can be spread by skin contact in sports called herpes gladiatorum, or cause finger infections, herpetic Whitlow, sometimes seen in healthcare workers.

And HSV2?

HSV2.

HSV2 is primarily sexually transmitted.

The usual cause of genital herpes also becomes latent, typically in the sacral nerve ganglia near the base of the spine.

Can either type cause really serious problems?

Like in the brain?

Very rarely, yes.

Either type can spread to the brain, causing herpes encephalitis.

Inflammation of the brain.

Is that dangerous?

Very.

Especially HSV2 encephalitis.

High fatality rate if untreated.

Prompt treatment with a cyclover helps, but neurological damage can still occur in survivors.

Measles.

Used to be everywhere.

Now much rarer things to vaccines.

Measles, rubeola.

Caused by the measles virus.

Extremely contagious, spread by the respiratory route.

And the MMR vaccine changed everything.

Traumatically.

Almost eliminated it in the US.

Cases went from millions a year to very few.

Global effort, too, since there's no animal reservoir.

Deaths worldwide have plummeted.

But the vaccine isn't 100 % and some are still vulnerable.

Right.

About 95 % effective.

So breakthrough cases happen.

A big concern is infants under one year old.

Too young for the vaccine.

And maternal antibodies from vaccination aren't as strong or long lasting as from natural infection.

Makes herd immunity vital.

What are the classic measles symptoms?

Incubation is 10 -12 days.

Then cold -like symptoms.

Fever.

Followed by the macular rash, flat red spots.

Starts on the face, spreads down.

And those spots inside the mouth.

Coplic spots.

Key diagnostic sign.

Small red spots with tiny blue -white centers on the inside of the cheek.

Appear before the skin rash?

And measles isn't just a rash.

It can have serious complications.

Definitely.

Especially dangerous for infants and the elderly.

Ear infections, pneumonia are common complications.

Encephalitis can occur, causing permanent brain damage.

And that rare late complication.

Subacute sclerosing panencephalitis, SSPE.

Fatal progressive neurological disorder.

Develops years after measles infection.

Another reason vaccination is so critical.

What about rubella?

German measles?

Is that as bad?

Rubella itself is much milder.

Often goes unnoticed.

Macular rash, light fever, complications in kids are rare.

So why the fuss?

Why is it in the MMR vaccine?

Because of congenital rubella syndrome, CRS.

If a pregnant woman gets rubella, especially in the first trimester, disaster.

How bad?

About a 35 % chance of severe fetal damage.

Deafness, cataracts, heart defects, intellectual disability, or fetal death.

So preventing rubella in pregnant women is the key.

Absolutely.

The rubella vaccine, introduced in 1969, protects most people for at least 15 years.

It has drastically reduced CRS cases.

Huge public health success.

Vaccination before pregnancy is crucial.

Are there other common viral rashes?

Like fifth disease?

Yes.

Fifth disease or erythema infectiosum, caused by parvovirus B19, often has that distinctive slap cheek facial rash in kids.

Can affect adults differently.

Yeah, can cause anemia or arthritis in adults.

What about rosiola?

Rosiola, common mild childhood illness.

Caused by human herpes viruses 6 and 7, high fever first, then a rash appears as the fever breaks.

And hand, foot, and mouth disease.

Sounds descriptive.

It is.

Caused by several enteroviruses.

Spread by contact with mucus, saliva, very common in day cares.

Causes a rash where?

On the hands, feet, and in the mouth, tongue, inside cheeks.

Flat or raised spots, sometimes little blisters, usually mild, but certain strains like enterovirus 71 have been linked to more serious neurological issues like encephalitis or meningitis, though that's less common.

Okay, we've covered bacteria and viruses.

Let's move to fungi.

The skin's resistance to drying actually makes it a target for some fungi, right?

It does.

Fungi that colonize the outer layers, hair, nails, epidermis are called dermatophytes.

And the infections they cause are dermatomycosis or ringworm?

Exactly.

Dermatomycosis, but commonly called tinias or ringworm.

But it's not a worm.

Correct.

Classic misnomer.

Called that because the infections often expand circularly.

What are the common types?

Tinea capitis scalp ringworm, tinea crurus jock itch,

tinea pedis athlete's foot, and tinea unglum fungal nail infection.

How do you get these?

Direct contact, contaminated objects, towels, floors, combs, even from infected pets.

What fungi cause them?

Three main groups.

Genera, really.

Trachophyton, microsporum, and epidomophyton.

They vary slightly in what tissues they prefer.

Hair, skin, nails.

And treatment.

Creams.

Often topical antifungals work for skin infections like athlete's foot or jock itch.

But infections involving hair or nails are tougher to treat, often requiring oral antifungal medications for weeks or months.

Are there deeper fungal infections?

Yes.

Subcutaneous mycosis.

More serious.

These fungi live in soil, on decaying plants.

Get in through small wounds like a thorn prick.

Grow under the skin.

Right.

In the subcutaneous tissue.

The most common one in the US is sporotrichosis, caused by sporothrax shinkii.

What does that look like?

Often starts as a small ulcer, typically on the hands of gardeners or farmers.

Can spread along lymphatic channels, usually treatable with oral antifungals like a trichonazole.

Not usually fatal.

And then there's candidases.

Yeast infections.

Caused by Candida aldicans.

It's actually part of a normal microbiota, usually kept in check by bacteria, especially in the mouth and genitourinary tract.

But it can overgrow.

Yes.

If antibacterial drugs wipe out the competing bacteria, or if there are pH changes, or if the person is immunocompromised, Candida can seize the opportunity and overgrow.

So taking antibiotics can lead to a yeast infection.

Absolutely.

A common side effect.

Newborns often get thrush a white Candida overgrowth in the mouth.

And it's a frequent cause of aginitis.

You get serious.

In immunosuppressed people, like AIDS patients or transplant recipients, Candida infections can become systemic spread through the bloodstream.

That can be life -threatening.

Treatment.

Topical antifungals like myconazole or nystatin for localized infections.

Systemic infections need stronger drugs like fluconazole or echinocandins.

Bacteria, viruses, fungi.

What about parasites on the skin?

Two common ones involving arthropods.

Scabies and lice.

Scabies.

Sounds incredibly itchy.

It is.

Intense itching caused by a tiny mite, Sarcoctus scadii.

The female mite burrows under the skin to lay eggs.

You can see the burrows.

Sometimes.

Thin, wavy lines, especially between fingers, on wrists.

It's spread by close, prolonged skin -to -skin contact.

Common in families, nursing homes.

How is it diagnosed and treated?

Diagnosis usually involves looking for the mites or eggs in skin scrapings under a microscope, treated with topical creams like permethrin or sometimes oral ivermectin.

Okay.

And then lice.

Especially head lice in kids.

Pediculosis is the infestation.

Head lice, pediculus humanus capitis, are spread mainly by direct head -to -head contact.

The female lays eggs, knits, cemented to hair shafts.

Do head lice spread disease?

That's a common worry.

No, thankfully.

Head lice do not transmit diseases.

They're just annoying and cause itching.

But body lice are different.

Very important distinction.

The body louse, pediculus humanus corporis, is a different subspecies.

It lives in clothing seams, not usually on the body itself.

And it can transmit diseases like epidemic typhus, especially in crowded, unhygienic conditions.

So head lice just cause itching?

Yes.

The itching is from sensitization to their saliva.

Scratching can lead to secondary bacterial infections, though.

How do you treat lice, especially with resistance emerging?

Non -prescription insecticides like permethrin or pyrethrins are common first tries.

But resistance is a growing problem.

Prescription options include malathion or lindane, though lindane has safety concerns.

Oral ivermectin is sometimes used.

What about nonchemical methods?

Newer silicone -based products work by physically smothering the lice, and meticulous combing with a fine -toothed knit comb to remove lice and knits is crucial.

Some places even have professional lice removal services now.

Wow.

Okay, finally, let's turn to the eyes.

Also exposed, also vulnerable.

Very vulnerable.

The conjunctiva, that thin membrane lining the eyelid and covering the white part of the eye, is a common entry point.

And inflammation there is conjunctivitis.

Pink eye.

Exactly.

Conjunctivitis, commonly called red eye or pink eye.

What causes it?

Bacteria.

Virus.

It can be either, or even allergies.

Haemophilus influenzae is the most common bacterial cause.

Adenovirus is often caused viral pink eye, which is very contagious.

And contact lenses are a risk factor.

Definitely.

They increase the risk, especially soft lenses worn for long periods.

Pseudomonads, remember them, can cause serious damage if they contaminate lenses.

So proper care is essential.

Absolutely critical.

Never use homemade saline.

Follow cleaning instructions meticulously.

Avoid sleeping in lenses unless they're specifically designed for it.

Let's talk specific eye infections.

There's one affecting newborns.

Yes.

Ophthalmia neonatorum.

Severe conjunctivitis caused by Neisseria gonorrhea.

Acquired during birth from an infected mother.

Causes a lot of pus.

High risk of blindness.

Yes.

Lots of pus.

High blindness risk if untreated.

Used to use silver nitrate drox for prevention.

Now antibiotic ointments like erythromycin are standard.

Partly because chlamydia co -infection is common.

Speaking of chlamydia, what's inclusion conjunctivitis?

Also caused by chlamydia trachomatis.

It's an obligate intracellular parasite that has to live inside host cells.

How do you get that?

Infants can get it during birth, too.

It can also spread in unclorinated swimming pools.

Swimming pool conjunctivitis.

Treated with tetracycline ointment.

And maybe the biggest infectious eye disease globally.

Trachoma.

By far.

Trachoma, also caused by certain types of chlamydia trachomatis, is the single leading cause of infectious blindness worldwide.

Affects hundreds of millions.

Blinds millions.

Where is it most common?

Prevalent in poor arid regions of Africa and Asia.

Also occurs in some indigenous populations in places like Australia and even the southwestern U .S.

How does it cause blindness?

It's the repeated infections, right?

Exactly.

It's transmitted by hands, contaminated towels, even flies.

Repeated infections cause chronic inflammation of the conjunctiva.

Leading to scarring.

Yes.

Scarring of the inner eyelid.

This causes the eyelashes to turn inward, a condition called tracheosis.

And the turned in lashes scratch the cornea.

Constantly.

With every blink.

This abrasion leads to corneal scarring, clouding, and eventually irreversible blindness.

Is there anything that can be done?

Yes.

Surgery can correct the tracheosis.

Antibiotics like azithromycin are effective, especially in mass drug administration programs.

But the real key is the WHO's safe strategy.

Surgery, antibiotics, facial cleanliness, and environmental improvement, like sanitation and fly control.

A multi -pronged approach.

Okay, beyond bacteria, what else infects the eye, especially the cornea?

Inflammation of the cornea is keratitis.

A common cause is herpetic keratitis.

From the cold sore virus, HSV1.

Yes.

The virus is latent in the trigeminal nerve, which also serves the eye.

Reactivation can cause corneal ulcers.

It's a leading cause of infectious blindness here in the U .S.

There's one caused by an amoeba.

That sounds unusual.

It is acanthamoeba keratitis, caused by acanthamoeba protozoa.

These amoebas are found in freshwater, tap water, hot tubs, soil.

How do people get it in their eye?

Almost always linked to contact lens wear, especially improper disinfection, or rinsing lenses, or cases with tap water, or using homemade saline.

Is it serious?

Very.

Starts mild, but progresses to severe pain.

Can destroy corneal tissue, often requiring corneal transplant.

In worst cases, the eye might need to be removed.

A powerful reminder about contact lens hygiene.

So we've covered a lot of specific diseases,

but the source material also talks about a bigger picture.

Neglected tropical diseases, NTDs, what are those?

It's a really important concept in global health.

NTDs are a group of, well, currently about 20 diseases, that disproportionately hammer the world's poorest populations.

Over a billion people affected.

In the least developed areas.

Exactly.

They cause immense suffering.

Blindness, disfigurement, organ damage, cognitive impairment, really trapping people in poverty.

And neglected, because they don't get enough attention or funding.

Precisely.

Compared to the big three, HIV, AIDS, TB, malaria, they often fly under the radar, despite their huge collective burden.

And some of the diseases we discussed today fall into this category.

Yes.

Both trachoma and Baruli ulcer are considered NTDs.

So what's being done?

The WHO has targets for control and elimination.

Strategies often involve things like mass drug administration, preventive chemotherapy, vector control, improving water and sanitation, managing animal reservoirs, and ensuring early diagnosis and treatment access.

It really shows how health is linked to poverty, sanitation, and basic infrastructure.

It really connects everything together.

It does.

Simple interventions can have a massive impact.

Well, that wraps up our deep dive into the microbial world of our skin and eyes.

It's amazing stuff.

From the skin's own defenses,

to how bacteria, viruses, fungi, parasites cause disease.

Definitely not just simple outer layers.

Not at all.

Understanding these microbes helps us grasp common things like acne or pink eye, but also huge global challenges like trachoma.

It really highlights that constant invisible battle happening right on us all the time.

We really hope this deep dive gave you some of those aha moments, maybe a new appreciation for the microbiology happening on your own body.

Keep that curiosity going.

Thank you so much for joining us on this exploration.

We're really glad you chose to be part of our last -minute lecture family.

Until next time.