Chapter 34: Eukaryotic Pathogens: Fungi, Protozoa, and Helminths

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All right, welcome back to the deep dive.

You know the drill, you send us the source material and we - When we take a deep dive into it, really dissect it.

Exactly, so think of this as a guided tour through a chapter.

This time around, we're tackling something.

Pretty crucial, yeah, parasitic infections.

Yeah, specifically visceral and blood and tissue.

Two major categories.

And we'll touch on some related fungal stuff too.

Yeah, so it's gonna be a fun one.

So the chapter starts off with a pretty good overview, defining what these visceral parasitic infections actually are.

Right, right, so they're caused by these pathogenic protozoa, which in simpler terms are single -celled organisms.

And the crazy thing is, the diseases they cause, well, they can be anything from mild.

Like a simple stomach ache, right?

Yeah, like gastroenteritis, to something way more serious.

Like meningoencephalitis?

Yeah, exactly.

That's when the brain and the membranes around the brain get inflamed, super dangerous stuff.

No kidding.

So how do these microscopic troublemakers actually get inside us?

Well, the chapter lays out a few ways.

Contaminated food and water are the usual suspects.

You know, these parasites can hang out in the environment just waiting to - Hit your ride.

Exactly.

And sometimes, they can even spread directly from person to person.

Okay, so hygiene is key here.

Now, the chapter also takes a moment to define what parasitism actually is, just to lay the groundwork.

Yeah, it's a symbiotic relationship, essentially.

Two different organisms interacting, you know.

The parasite and the host.

And what's the defining feature here?

Well, the parasite's got a benefit, right?

Often, it's by siphoning off nutrients from the host, and the impact on the host, that can be a mixed bag.

Sometimes, it's minimal, but often, it's not so great.

Right, and as the chapter highlights, a huge number of these protocists are responsible for parasitic diseases in humans.

It's like a whole world of microscopic mayhem.

It really is.

The chapter then does a nice job of making a distinction, you know, between visceral infections and those that hit the bloodstream and other tissues.

Okay, so visceral infections are those the ones mainly in the gut.

Yeah, primarily affecting the internal organs.

Often leading to intestinal issues.

And then you have the infections that target the blood and other tissues throughout the body.

So it's like, one's more localized, the other systemic.

Got it.

And it's kind of humbling to think that some of the most significant diseases in history, like malaria,

are parasitic.

For sure.

And the chapter points us to table 34 .2, which gives a breakdown of major parasitic human diseases.

It lists the culprit, the target organ, that sort of thing.

Okay, that's a handy reference for the listener.

Now, the chapter moves on to some specific examples, starting with amoeba and ciliates, and temeba, nigleria, and belentidium.

Names that don't exactly roll off the tongue, but sounds like they pack a punch.

They can, yeah.

And temeba and nigleria, they're both part of this group called amoeba zoa.

And what's interesting about them is how they move.

They use these things called pseudopodia, which are like temporary extensions of their cell.

So they don't swim, they kind of ooze along.

More or less.

And the chapter even directs us to section 18 .8, if we want to dig deeper into how that works.

We'll save that for another deep dive, maybe.

But in terms of the infections they cause, are they both equally problematic?

Well, both entomeba and nigleria can cause some serious problems, even fatal infections.

But nigleria infections, those are actually super rare.

So while the outcome can be bad, the chances of encountering it are slim.

Okay, so rare, but potentially devastating.

Good to know.

And then there's belentidium.

Belentidium's a bit different.

It's a ciliated alveolate, meaning it's covered in these hair -like structures called cilia, which it uses to move and eat.

The chapter points us to section 18 .4 for more on that.

Belentidium infection is mainly a concern in tropical areas.

More geographically concentrated.

The chapter then focuses on a specific type of entomeba.

Right, entomeba histolytica.

This is the one behind amoebiasis.

Ah, amoebiasis, another intestinal illness.

Exactly, another one of those visceral parasitic infections.

Now the chapter also brings in some visuals, figures 34 .4 and 34 .5, showing subcutaneous and systemic mycosis.

Can you walk us through those?

Sure.

Figure 34 .4, that's all about subcutaneous mycosis.

These are fungal infections, but they go deeper than just the surface of the skin.

It shows spore trichosis, which is caused by sporothryx chenki.

And then there's chrymoblast mycosis on a hand, caused by pheolephora varicosa, though other fungi can be involved too.

So these are the ones that burrow deeper.

And figure 34 .5, that's about the systemic ones, right?

Yep, systemic mycosis, these are the ones that spread to internal organs.

So it shows a few examples.

Histoplasmosis with histoplasma, yeast cells in the spleen.

Cutaneous blastomycosis on an arm, which is a bit of a confusing name because it's on the skin, but it can also become systemic.

Then there's cryptococcosis with cryptococcus in the lung.

Coccidioidomycosis, same idea, yeast cells in the lung.

And then paracoccidioidomycosis with lesions on the face.

And finally, oral thrush, caused by candida albicans in the throat.

Wow, that's a lot of different ways fungi can mess with us.

It's incredible how these different fungi can cause such a range of problems.

The chapter also mentions that figure 34 .1 shows images of these fungi under a microscope.

Right, so you can actually see what these things look like.

Okay, so we've covered some of the fungal stuff.

Switching back to parasites, there are a few more that primarily target the gut, right?

Yeah, there's Giardia intestinalis, which causes Giardiasis.

Another one you can get from contaminated water.

Then there's cryptosporidium parvum, causing cryptosporidiosis, also mainly affecting the GI tract.

And finally, Toxoplasma gondii, the cause of toxoplasmosis, which often presents with gut issues, but can also affect other parts of the body, especially in people with weakened immune systems or during pregnancy.

These are names that might ring a bell for people who've had some unfortunate experiences with food poisoning or contaminated water.

And the chapter even shows us Toxoplasma gondii up close, right?

That's figure 34 .11.

It shows these tachyzoites, which are basically the rapidly multiplying form of Toxoplasma inside a heart cell.

The caption mentions that they're super tiny, like four to seven micrometers long.

And it directs us to figure 18 .11B if we wanna see what the sporozoites look like.

Those are the infectious stage.

It's amazing how these tiny things can cause so much trouble.

Okay, so moving on.

The chapter shifts gears a bit.

Yeah, next up is blood and tissue parasites.

Okay, so now we're talking about parasites that take up residence in the blood and other tissues.

And of course, we can't talk about this without mentioning malaria.

Absolutely.

Correct.

Malaria is caused by different species of this genus called plasmodium.

And there's even an art activity that goes with figure 34 .12, which probably shows the whole life cycle of plasmodium from the mosquito to the human and back again.

Yeah, malaria has been a scourge for humanity for centuries.

What are the traditional ways of treating it?

Well, quinine -based drugs have been the go -to for a long time.

Chloroquine's probably the most famous one.

It works by killing the merozoites, which are the stage of plasmodium that infect red blood cells.

So it attacks the parasite when it's in the blood.

Exactly.

But the catch is it doesn't kill the sporozoites which hang out in the liver.

So it's like hitting one stage, but not the other.

So that's why malaria can be so tricky to get rid of completely.

Right, that's where primocaine comes in.

It targets the sporozoites in the liver, especially for plasmodium vivax and plasmodium oval infections.

So using both chloroquine and primocaine can be much more effective in preventing relapses.

So it's like a one -two punch.

What about newer treatments for malaria?

Well, there's artemisinin.

This one's pretty interesting because it comes from the wormwood plant, which has been used in traditional medicine for ages.

But now we can also produce it using genetically engineered yeast.

Wow, that's pretty cool.

The chapter mentions section 12 .1 on and figure 12 .37 if you wanna dive into the biotech behind that.

And figure 34 .43 probably shows us some more visuals of plasmodium and the effects of malaria.

It's amazing how traditional knowledge and modern science can come together like that.

Now, beyond just treating the infection, what about controlling the spread of malaria?

Well, a lot of the efforts have focused on mosquito control.

Things like draining stagnant water where they breed, using insecticides, that sort of thing.

And these strategies have been really successful, especially in the U .S., where malaria has been mostly eradicated.

That's a testament to what public health measures can achieve.

What about a malaria vaccine?

That's the dream, right?

Yeah.

But it's proven really challenging.

The chapter mentions that there are a bunch of vaccine candidates in development, some using peptides, some using recombinant particles, even DNA technology.

Yeah, I remember reading about those in previous chapters, sections 12 .8 and 28 .3, I think.

Right.

But as of when this chapter was written, there's still no widely effective vaccine for mass vaccination programs.

So still a work in progress.

The chapter then moves on to another group of parasites, leishmania, which cause leishmaniasis.

Yes, and leishmania can cause a couple of different forms of the disease.

Cutaneous leishmaniasis, which affects the skin, and visceral leishmaniasis, which affects internal organs.

Let's start with cutaneous leishmaniasis.

What are the key features of that one?

Well, it's usually caused by leishmania tropica and leishmania major.

And the main thing is that you get these skin ulcers at the site of a sandfly bite.

Sandflies are the culprits here.

Yep, and these ulcers can be pretty nasty, sometimes leaving permanent scars.

The chapter mentions that cutaneous leishmaniasis is found in over 88 countries, mostly tropical and subtropical, about a million new cases every year.

And get this, there are even occasional cases reported in the US, mostly in Texas.

So not just a tropical disease anymore, how do they treat it?

Antimony injections are the standard treatment.

Though sometimes they have to use other drugs if the parasite is resistant or it's a different species of leishmania.

Okay, so that's the skin version.

What about visceral leishmaniasis?

Sounds like it goes deeper.

You got it.

Visceral leishmaniasis caused by leishmania donovani is definitely more serious.

The parasite spreads from the bite to the internal organs, the liver, spleen, bone marrow.

Yikes, and what happens if it's not treated?

Well, it's almost always fatal.

It causes fever, chills, your blood cell counts drop, and your spleen and liver get huge.

It's a really bad scene.

Sounds awful.

What are the treatment options for that one?

Antimony, again, is the main treatment, but you also need supportive care, like rest.

And sometimes if blood counts get too low, they have to do blood transfusions.

So not a walk in the park.

Definitely not.

The chapter mentions that there are about 300 ,000 new cases globally each year and about 20 ,000 deaths.

It's a significant public health issue.

No kidding.

And the chapter even talks about the risk of leishmaniasis increasing in the future.

Right, it basically says that sandflies are spreading their range because of climate change and deforestation.

So they estimate that almost 400 million people are at risk.

That's like 5 % of the entire world population.

Wow, that's a sobering thought.

Okay, next up, the chapter introduces trypanosoma, another tongue twister.

Trypanosoma bruchii is the one that causes trypanosomiasis, also known as African sleeping sickness.

And then there's trypanosoma cruzi, which causes Chagas disease or American trypanosomiasis.

Both are blood and tissue parasites.

So two different diseases, but caused by related parasites.

Let's start with African sleeping sickness.

How's that one transmitted?

Tinty flies.

They're found in Sub -Saharan Africa.

And the parasite, it starts in the blood and lymph, but eventually gets into the central nervous system.

Uh -oh.

Yeah, that's when the neurological symptoms start.

The lethargy, behavior changes, even coma.

And if it's not treated, it's fatal.

That sounds rough.

What about treatment options?

Well, that's the problem.

The drugs are toxic and there's growing resistance.

And to make matters worse, there's no vaccine.

So prevention and early diagnosis are crucial.

Absolutely.

Now Chagas disease is different.

It's named after Carlos Chagas, who discovered it.

And it's spread by these redovid bugs, which are sometimes called kissing bugs, because they like to bite people on the face while they sleep.

Kissing bugs, charming.

The chapter even shows us some pictures in figure 34 .15CND.

Chagas disease is mainly found in Latin America.

And what's different about trypanosomal cruzi is that it can affect a lot of different organs, the heart, the gut, the nervous system.

It causes chronic inflammation and tissue damage.

What are the long -term consequences of Chagas disease?

Well, the acute phase might not be so bad, but a lot of people develop chronic Chagas disease, which can cause some serious problems, especially with the heart.

It can even lead to premature death.

And there's no cure that parasite can stick around for life.

So early treatment is key here.

Definitely.

There are drugs like benzinidazole that can help, but they work best in the acute phase.

And just like with African sleeping sickness,

there's no vaccine for Chagas disease.

So prevention is still a big challenge.

Okay, last but not least, the chapter talks about schistosoma mansoni, which causes schistosomiasis.

Right, schistosoma mansoni.

And it's important to point out that this one's a bit different.

Schistosoma is a helminth, which means it's a parasitic worm, not a protozoan like we've been talking about.

So it just shows you the variety of parasites out there.

Okay, so we're talking about a worm now.

What can you tell us about schistosomiasis?

It's a disease that's mostly found in tropical areas, especially in Africa, but also in some parts of Latin America and the Caribbean.

And it's often linked to poverty and poor sanitation, because the parasite needs these freshwater snails to complete its life cycle.

So it's tied to environmental factors as well.

Exactly.

Schistosomiasis is a chronic disease.

And over time, it can damage the liver, spleen, bladder, and cause all sorts of problems from the buildup of fluids and worm eggs in the body.

That doesn't sound good.

How do they diagnose and treat it?

Well, the good news is that it's relatively easy to diagnose.

They just look for the parasite eggs in the urine or feces.

And there's an effective drug called Prasicontel that works pretty well.

Okay, so at least there's a treatment for that one.

What about the overall impact of schistosomiasis?

It's a major global health problem.

While the death rate is relatively low, only about 0 .1%, it's actually the second most common parasitic infection worldwide, right behind malaria.

In 2017, over 220 million cases were treated, but they think the actual number is much higher because many people don't get diagnosed.

Wow, that's a staggering number.

So even though it's not as deadly as some other parasitic diseases, it still affects a huge number of people.

And to wrap things up, the chapter ends with a glossary of terms.

Yeah, just a quick recap of some of the technical terms we encountered,

like subcutaneous mycosis and superficial mycosis, which are different types of fungal skin infections, and then systemic mycosis, which are the ones that affect internal organs.

It also defines trypanosomiasis and schistosomiasis again, just to make sure we're all on the same page.

A handy reference.

Well, there you have it.

A deep dive into the world of visceral and blood and tissue parasites, and even some fungal infections thrown in for good measure.

We've covered it all, the main points, the theories, the research, the examples.

Hopefully you're feeling a bit more knowledgeable now.

And as we wrap up, we wanna leave you with something to think about.

As the world changes with climate change and globalization and all that, what new challenges might we face when it comes to these parasitic and fungal diseases?

Food for thought.

Thanks for joining us on this deep dive.

We encourage you to keep exploring these topics and learning more about the fascinating world of microbes.

Until next time.

See you then.