118. The Moulds: Aspergillus part 1, overview

Alyssa and Callum talk through Aspergillus, the first of our Moulds series. After you hear the puns in this episode you'll be fumi(n)g at us. Tune in to hear about:

• Epidemiology
• Taxonomy
• Pathogenesis
• Lab identification

On the next episode we'll be joined by some special guest to delve into the clinical aspects of the Aspergillosis.

Notes for this episode here: https://idiots.notion.site/118-Moulds-Aspergillus-ce3ba58d045b47b18d9641b56559c6f5?pvs=74

Transcript

0:00

Hi everyone. Welcome to the Idiots Podcast. That's infectious disease insights of these specialists. I'm Callum, and that's Alyssa. And we're going to tell you everything you need to know about fungal infection. Soon, may the editing come to discontinue the Tazo sun one day when the S piece done, we'll take our leave and go.

Callum: 0:22

Hello, Alyssa.

Alyssa: 0:24

hi, Callum, how are you?

Callum: 0:25

I am. I am. Great. I'm en enjoying the Scottish Sun. How are you?

Alyssa: 0:30

Yeah, great. Also very sunny down here and I've got some exciting news.

Callum: 0:35

Oh,

Alyssa: 0:35

I've recently got a dog.

Callum: 0:37

oh, great.

Alyssa: 0:38

Yeah.

Callum: 0:39

type of dog is it?

Alyssa: 0:40

So it's a collie. It's called Gina, but we're gonna call it G for sure. It, yeah, and it's great. Yeah, I love my colleague g.

Callum: 0:53

I had no idea where that was going.

Alyssa: 0:57

It's pretty awful. I don't have a dog.

Callum: 0:59

Yeah, I, I have a friend called Jill who's got Colie, so I guess your dog, is the same as hers. As per Jill's.

Alyssa: 1:08

I do actually have a cat that is true.

Callum: 1:10

oh.

Alyssa: 1:11

Called Brian, good, solid name,

Callum: 1:15

a good name for a

Alyssa: 1:15

so I call him Bri Sous.

Callum: 1:18

Oh no. I didn't realize was a pun. I thought you were just saying I thought a genuine,

Alyssa: 1:25

It is genuine. I do genuinely have a cat called Brian.

Callum: 1:28

oh, okay. Well, I don't have any pets. I can't make any pet related puns. Uh, are we talking about today?

Alyssa: 1:38

So today we are gonna talk about aspergillus, and we are gonna run through a bit of an introduction, to this fungus.

Callum: 1:46

Yeah. Yes. This is part one of. Jane and I are going to slash already have, but for the purposes of this are going to speak to experts in aspergillosis about this, or more clinical aspects and treatment. So we thought it would be helpful to HA an introduction to Aspergillus So I guess, what is Aspergillus? I.

Alyssa: 2:12

So aspergillus is a mold, and it's, I think it's the most common, mold to cause disease in humans. So it's like many of these. Disease causing molds in humans. It's environmental, it's a sapr prophetic mold. And the disease that it causes is known as aspergillosis.

Callum: 2:37

And what does S prophetic mean?

Alyssa: 2:39

Sapr prophetic means that it digests, organic material, so it uses organic material for. Its source of nutrients

Callum: 2:50

So that could be an environment or it could be

Alyssa: 2:54

in the,

Callum: 2:55

human Yeah. Damaged tissue. Okay. And I guess aspergillosis it's quite a wide spectrum, isn't it? So all the way from, an allergic response to aspergillus or aspergillus antigens all the way up to acute invasive aspergillosis, which is severe. I guess you're saying it's ubiquitous in the environment, so why do we not all have aspergillosis?

Alyssa: 3:21

So, aspergillus produces spores as many environmental molds do. And. We inhale, and thousands of spores every day. And our immune system, if we have a well-functioning immune system, is able to clear those. So aspergillus only causes disease in hosts who have, predisposing underlying conditions, say such as immunocompromised, or patients with underlying lung conditions. And that's really important for the spectrum as well. So the type of disease that aspergillus will cause, really depends on the host's underlying, predisposing condition. I.

Callum: 4:05

Hmm. So if you've got an intact immune system, you're more likely to get an allergic response. If you've got a compromised immune system, you're more likely to get invasive. I guess we see that spectrum and, lots of different diseases. so when we say aspergillus, what do we mean by that? That's a genus. So, there's quite a few different types of aspergillus species. How many are there, are we gonna do an alternating name? I don't know.

Alyssa: 4:35

We can. Yeah, so I think it's a huge. And it contains over 200 different species and any of these can essentially cause allergic disease. So if the host has an overactive immune response, they can develop allergic reaction to these, these fungi, and there's probably about 20 that cause invasive fungal infection. But the top four of these are with the top one being aspergillus fumigatus. As Aspergillus TEUs,

Callum: 5:11

aspergillus, Nigel.

Alyssa: 5:13

And I think Aspergillus Fumigatus accounts for the majority of infections in humans, and it's also a WHO critical priority fungal pathogen. And one of the major emerging concerns about this. Fungus at the moment,, is that there is a rise in AAL resistance within aspergillus fumigatus, and that's the first line treatment for infections with this fungus. And that's linked to the widespread use of AALS as fungicides in agriculture. So that's a, a major current concern

Callum: 5:47

Hmm. Yeah, it's deeply concerning. And I guess we, we do rely on azoles as our, as our treatment as become on until later. So there's 250 species and they're classified into. Seven sub genera that are in turn subdivided into several complexes.

Alyssa: 6:12

Yes.

Callum: 6:13

And so the species can be grouped into these complexes. And the reason for that is that many of the species have overlapping morphological characteristics and because they can't be distinguished morphologically, they're clustered into these complexes because that makes a lab work a lot easier, doesn't it? So if you're going to genetically, that's the thing about taxonomy,'cause we're talking about taxonomy now, I guess, that it's all very well the taxonomist. Doing complex genetic tests and saying, oh, that's not this, that's this. ultimately in the laboratory we're mostly working on phenotypic features to identify, so what are these complexes?

Alyssa: 6:59

Yeah, so again, it really relates to the main species that, that cause, invasive disease. And not species in isolation, but are actually complexes that include other, similar species. So there's aspergillus, fumigatus Complex, which includes species such as aspergillus lentils, which is much less common cause of human infection. But often when you see it, the Id reported it might be reported as aspergillus. fumigatus complex. Which I know I, it's taken me a little bit of time to get my head around what that actually means.

Callum: 7:39

Yeah, I've not, I hadn't actually come across that until now. I think we just report it as Asperger's Fumigatus, I guess it's probably the, on the reference laboratory reports and so on. Yeah, often when you get the sort of unusual organism name, you're perplexed by it. But I guess if it fits into the complex, that's quite useful. And then the other ones are Asperger's. Flavus complex. tereus Complex. niger complex, and nidulans complex. Yeah. Okay. So that's quite useful to understand. So what's the epidemiology of Aspergillus? Where do we find this?

Alyssa: 8:13

So they're all around us in the environment, and they're found worldwide. So it's not particularly located to, specific regions of the globe. And. They cause opportunistic disease, as we said, in patients with predisposing conditions. And the type of disease people get depends on their underlying condition. And that's generally how we get this spectrum of disease with aspergillosis. So starting with allergic disease, that almost exclusively occurs in patients with asthma or cystic fibrosis. Then there's chronic forms of aspergillosis, which can occur in patients who don't really have, immune compromise, but have underlying lung condition, such as COPD or tb. Or nontuberculous mycobacterial disease, cystic fibrosis, sarcoidosis, or asthma. And then your invasive and disseminated disease occurs in immunocompromised patients. So those, with immuno compromising risk factors such as hematological malignancy, prolonged neutropenia, long-term steroids, transplant recipients. HIV with low CD four count. Those sorts of gr groups of patients. And it's, associated with huge amount of global morbidity and mortality. So over 2 million patients are estimated to develop, invasive aspergillosis annually with mortality of about 85%. And I think it's. What we've discussed previously, it's the striking mortality from invasive fungal infection. That's really, really scary.

Callum: 9:53

You mentioned that in that fungal overview episode, and it's striking how despite there not being as many cases of invasive fungal disease, the mortality is so high. So how does it act? How does aspergillus actually cause the disease? What mechanisms does it use to, to make people ill?

Alyssa: 10:13

So, as we've said, aspergillus produces spores that are around us in the environment. So we come into contact mainly through inhalation of these spores. Through the nasal passages into the lungs, also inoculation of wounds. And in immunocompetent patients, these inhaled spores or kedia are generally phagocytose and cleared and infection is prevented. It is very rare that invasive, aspergillosis occurs in immunocompetent individuals, but not unheard of. So if you get a massive exposure. Or inhalation of spores such that the immune system is overwhelmed. You can rarely get cases in immunocompetent individuals, but it is predominantly your immunocompromised. So in your immunocompromised, the inhaled or inoculated spores, aren't effectively cleared by the immune system. So then germinate and produce hyphy, which are then able to invade the lung tissue. Or the local tissue to where they've been inoculated. And then if the immuno compromising conditions particularly severe, such that these high fear are able to grow and grow into the bloodstream causing angio invasion, you can then get disseminated infection to other areas of the body.

Callum: 11:36

That's things like the eyes, the skin. Yeah. And then I guess in patients who've got underlying lung disease but aren't necessarily, immune compromised, there essentially your damaged lung becomes colonized. So I don't believe Aspergers is part of the normal flora of the lung, unlike Canada, which are, and, this colonization means that, you've got this slow fungal growth. Which leads a chronic pulmonary aspergillosis because the lung tissue is damaged. The, aspergillosis is able to replicate in that, setting. And particularly if there's things like cavities. So you know, that might be like post TB would be a good example of cavitatory disease and you can get something called an asper, which is the sort of big. Ball of a big fungal colony that grows in there and it's got quite a typical radiological appearance. So that's certainly something to consider in the post TB and other cavitary lung disease patients.

Alyssa: 12:32

And then I guess part of the spectrum that we are probably as infection doctors least experienced with, and this probably falls more into the respiratory physicians, is the allergic disease. So the. There's a group of patients who, develop, an allergic response to these inhaled spores. And then this can lead to a really wide spectrum of allergic disease depending on how severe that response is. So the different, the different pictures are asthma with associated fungal sensitization, severe asthma with fungal sensitization. And allergic bronchopulmonary, aspergillosus

Callum: 13:12

So yeah, and you mentioned that it can be inhaled. So if that's coming for the nasal roots, then you can also get sinus disease. and that again depends on the degree of the immune response. So you can get a sort of invasive fungal rhinoc sinusitis. So you can see that of other fungi like mucor as

Alyssa: 13:28

Mm-hmm.

Callum: 13:29

But it can be current aspergillosis. You can also get a certain more chronic picture, which is invasive and granulomatous. You can get Asperger. So the sinuses are ready made cavities in the head, I guess. Finally an allergic fungal sinusitis. So it is basically the things that happen in the lungs can also happen in the, nose and, the sinuses.

Alyssa: 13:52

And then, we've mentioned that aspergillus spores can get inoculated and cause disease at other sites so they can cause cutaneous disease. In the context of burns or contaminated wounds, I think a common, fairly common one that we see in immunocompetent patients is. Keratitis associated with contact lens use. And then ear infection, oto mycosis, which is particularly seen with aspergillus Nigel, and it causes a chronic otitis externer. So I guess that's one to consider in patients with, chronic OE that aren't, responding to antibiotic treatment.

Callum: 14:29

It can be really challenging because as we said already, it's ubiquitous, so aspergillus can often, I. to these sites, like some of chronic otitis externa, they had a lot of antibiotics, you can sometimes get aspergillus there as a colonizer. The same with cutaneous disease. So I think that's really tricky sometimes that bit of, you're in the laboratory, you've got a result that says they've grown aspergillus and trying to say that, is this clinically relevant or not? Because it can be, if it was always a contaminant, that'd be easy, but, there's this potential. So that's quite a challenging situation to manage, as a microbiologist, I think. So we're gonna skip over the sort of clinical aspect,'cause we'll come back to that. So maybe we could now just talk about, how this organism appears in laboratory and what diagnostics we might be able to use.

Alyssa: 15:22

Yeah, sure. It's a kind of similar group of diagnostics that, that we've already covered, in the diagnostics, session. But we can talk through. How this is useful specifically for diagnosing aspergillus. And I think what we often start off with is direct microscopy. So that's your most basic test, really looking at clinical samples and trying to see if you can see fungus there. And I think that can be helpful for what Callum was saying about differentiating infection from colonization in that if you see. Fungal hyphy, it's much more likely that this is infection rather than, just colonization with sports. So microscopy can be performed on respiratory specimens and tissue specimens, using either light microscopy or fluorescence microscopy with a fungal brightener, which makes detecting fungi much more, sensitive. Say something like Calor white. And the aspergillus hyphy, so they're clear or high in hyphy, they're generally quite thin. They have acute branches, and regular scepter. So that can help differentiate them from, other mold pathogens such as Muco Myas, which has a different appearance than the microcap. But you are not really able to, determine if this is aspergillus or fusarium. Based on that alone.

Callum: 16:54

Yeah. So yeah, that could be really useful. And then I guess once you've seen it on the microscopy, you'd then go on to trying to culture this, grown in saro or malt. and I guess how would it look, morphologically Because I guess unlike mycology as a much more, Fun I guess, laboratory thing.'cause you actually get to look at it and make decisions rather than just checking everything in the.

Alyssa: 17:21

Yes, you can get a really good idea of what gen or species a fungus is. A mold is from looking, looking at it on a plate and then dyeing the microscope. So the colonies generally grow fairly fast, and they often have like very faulty, top to the colonies where you've got all of these. These spores. And then identification is based partly on, the color and the colony color. So they can be white or yellow or brown, black shades of green, and that can give you an indication to, to which species or genus this might be. And then you can look at the. Fungus and the microscope and the morphology of the cidal head. So the, the part of the fungus that produces spores, can also give you an idea of identification. I think one of the main problems that I've found with this, it, you need to be quite experienced and, always refer back to a textbook, which, Tells you the different, morphological appearances of the different fungi. But something we've found is that the molds won't always sporulate, in the lab. And then, you're not really able to identify them morphologically if they haven't developed, fruiting bodies and sated.

Callum: 18:47

There's so many like different terms in mycology. It was

Alyssa: 18:50

Hmm.

Callum: 18:50

confusing to wrap your head around. So I think you've explained this pretty well, so I'm going to try and explain it from what you've written. and then you can tell me if I get it right or not.'cause I've spent quite a lot of time revising this. People talk about a candidaphore. That is a specialized hyphy. So hyphy is like the sort of growing I guess, of a fungus. Kedia war is the specialized hyphy on which the Kedia develop. And kedia are basically the spores that we've been talking about. The end of the Kedia four. a physical, so like a swelling I guess, and that's covered either a single, layer, of

Alyssa: 19:34

file lights.

Callum: 19:35

Ides. So that's the things that produce the canadia

Alyssa: 19:39

Yeah, the committee are born from the

Callum: 19:41

they're

Alyssa: 19:41

final.

Callum: 19:41

replicating and producing the canadia. And they can be either ary eight. Where there's a single layer they can have, something underneath them called mely. So it's mely and affiliated. And then the conidia come out and in which case it's called bi. Just a lot of Latin words, and it's quite confusing. Name-wise, they look quite distinct. The, basically it's just one layer or two layers. don't necessarily, I don't remember the names of those. But, that's quite useful if you're presented in an exam, for example, of a picture of a microscopy or fungus, which I think I had. So, it's certainly possible to be asked that question'cause it is, they're quite distinct, the different fungi, like when you know what they look like. Like if you sirium or aspers Nigel, like once you've seen it a couple of times, I think you can pick it up. And then also the way that they're distributed can be different. So they can either come out of this vesicle at the end of the committee of four, um, in a radiate way, so all around it. So sort of like a dandelion, head where you blow the seed off that that's radiate and then kilometers, coming up like a sort of crazy hairstyle, I guess. Is that about right? Explanation. Yeah, there's pictures in the show notes that Alyssa's, got, from Adelaide ology, so I think that's probably, it's quite hard to explain in an audio format, like some things are.

Alyssa: 21:05

But yeah, no, I think those are the main points. So you've got your, spore bearing cidal head, which can either be uni eight with a single layer of fides or bary eights with the layer of chui and then fides over the top, and then the spores, either radiates all the way out of the cle Yeah, the dandelion or in alumna fashion., Like a Marge Simpson hairy.

Callum: 21:31

Yeah, that's a.

Alyssa: 21:33

And these are lots of terminologies that you'll see in, in fungal identification textbooks. It's useful being familiar with them. So when you're faced with, looking at something down the microscope, you know what different structures to be. Trying to identify, to work out what the fungus might be.

Callum: 21:50

Yeah. And so there's a table in the show notes about, the different species, the colony pigmentation under their cidal head distribution. So you can have a look at that if you're interested. Maybe we could just give the example of Asperger fumigate and then people can have a look at more if they want. So how would you identify asperges fatu on, thats morphological appearance.

Alyssa: 22:13

So firstly it's colony appearance on the plates. The color, if it's correlated,, it has like a green, blue, colony color. And then if you were to do a cellar tape slide, with lact cotton blue staining, and look down the microscope. You would see, uniseriate columnar philaides that cover the top two thirds of the vesicle.

Callum: 22:38

Yeah, so there's a picture of that. I think the blue green is pretty classic and that being the most common one, you're gonna identify that a lot. But yeah, some of these, some of the, I was torn into Ecology Lab because a lot of the time it's like, it's beautiful in a way. It's, they're very colorful. They have these really complex structures, almost felt like that, like really unique appearances. actually just sidebar Eced, conference they, They, they often have these art stations. So this year they had a load of art from microscopy. It was like, and they had like agar art and stuff and it was like, so this, you can appreciate the beauty in it. Whilst also appreciating that these are like deadly pathogens,

Alyssa: 23:20

Yeah.

Callum: 23:20

significant disease. It's that sort of weird feeling when you look at it like, wow. But you're also like, yuck. So that's, that was the morphological identification. And what other diagnostics are supportive?,

Alyssa: 23:32

You can get so far with, Identifying and speciate aspergillus using morphology. But it does require experience and, and knowledge and then other methods of identifying it. So once you've grown the fungus, other methods are, molecular, and also moldy to, mass spectrometry, can be used for identifying molds.

Callum: 23:55

Hmm.

Alyssa: 23:56

And we covered that in, was it the second fungal diagnostic?

Callum: 24:00

fungal diagnostics. But I think the first fungal diagnostic episode with Prof Richardson, and we went through direct musco, direct microscopy and culture. And in the second part we talked about sort antigens and serology, et cetera. so I guess just to summarize that, for here we can use gala manin. We've also got our aspergillus antibodies, so IgG, to do chronic infection. But it could also be allergic syndrome or colonization. And in the IgE, which when combined with your total IgE can be supportive of a, a allergic reaction. And when, say people say aspergillus precipitants,, I think, to do with the way that the lab tests used to be done. So it

Alyssa: 24:42

Okay?

Callum: 24:42

precipitation test. So

Alyssa: 24:44

Hmm.

Callum: 24:44

like I think on our record itself calls it asper, precipitants

Alyssa: 24:48

so on the Manchester University website, there's good information about the different tests, and it says that Aspergillus fumigatus precipitins is a test to detect the presence of IgG antibodies to as aspergillus fumigatus. And it can be used useful to diagnose, pulmonary aspergillosis, Asperger and hypersensitivity pneumonitis. But not really used for investigating invasive, aspergillus

Callum: 25:22

okay,

Alyssa: 25:22

Invasive.

Callum: 25:23

Pacifican is the same as iGT?

Alyssa: 25:25

Yeah.

Callum: 25:25

So that's the antibody tests and It blew past that man, didn't I? But I think we did have quite a long discussion about that before.

Alyssa: 25:33

Yes.

Callum: 25:34

episodes. Diagnostic episodes. So you can go back to listen to that. What about Aspergillus, PCR?

Alyssa: 25:41

So Aspergillus, PCR, my understanding is that this, can be used to. Confirm a clinical suspicion of a osis. So not useful in allergic disease, but useful in invasive or chronic disease, in high risk patients. And it's tends to, in that setting, be performed on a respiratory specimen, but it can also be used as a screening test where it's performed on EDTA blood, to screen for, invasive asidosis in high risk patients?

Callum: 26:15

I didn't realize you could do that. Is that part of a protocol

Alyssa: 26:18

Yeah, I think if you had, post stem cell transplant patients, you can screen them periodically, for fungal infection. Like you might perform a B 2D glucan.

Callum: 26:29

Yeah. So I guess we'll talk a bit more about the diagnostic challenges, of, aspergillosis with, Ian and Darius in next episode. Just to finish off, maybe we could just lightly touch on antifungal sensitivity testing. So can we do antifungal sensitivity testing for aspergillus?

Alyssa: 26:51

We can. And, my understanding is that this would only really be done in a reference laboratory setting. And I think it's done by broth, micro dilution. And Ucas, do you have, susceptibility break points?

Callum: 27:07

Yeah, we're lucky to have UCA rate points for aspergillus. But as you say, I think it's done in the reference laboratory. I think in Nado North we, do some aspergillus MIC testing, because we've got the micro detter plates. But it's a pain to set up. But yeah, it's not the easiest to do. So would be referring this off to the reference laboratory.

Alyssa: 27:27

I guess one, one thing to touch on is just thinking about antifungal resistance, within aspergillus. And one notable species is, or species complexes aspergillus terrace, which it's worth remembering is intrinsically resistant to amphotericin B with some rare exceptions, but generally. Should be considered resistant to amphotericin B. And then as, we said in the introduction, one of the major concerns is this rise in azole resistance within Aspergillus Fumigatus, which appears to be related to agricultural use of ails as fungicides. Which is interesting because it's not a plant pathogen. So the ails used in agriculture aren't to target aspergillus, it's just a bystander in the environment that is then exposed, and develops resistance. And then there have been clinical cases where, you know, with resistance to AALS that have been linked back to, the agricultural use.

Callum: 28:35

Which is terrifying.

Alyssa: 28:36

Which is terrifying. Yeah.

Callum: 28:38

this I was in a talk about Resa fungi

Alyssa: 28:40

Mm-hmm.

Callum: 28:41

and, it was really interesting and, Rena Richardson, who was giving the talk there was talking about this exact issue. So it's a sort of, I guess a global health priority, isn't it? And deeply concerning. It's hard enough to treat fungi already without adding more antifungal resistance into the mix, isn't it? So there we've gone over the basics of aspergillus, what it is, the taxonomy, the epidemiology, pathogenesis, some of the laboratory diagnostics, building on what we talked about in those diagnostic episodes, with Malcolm Richardson before. And a little bit about the antifungal sensitivity testing and emerging resistance. In the next episode, we'll be going into more detail on the clinical aspects of diagnosis and management of this condition. So I guess all that remains to say is thanks so much, Alyssa, for preparing the excellent show notes, which I recommend you check out the link is in the episode description on your podcast player, and we'll see you next time for Aspergillus part two.

29:57

This Mycology series has been supported by the British Society for Medical Mycology. The BSMM aim to bring together clinicians and academic researchers in the field of medical mycology. For more information, you can find the link to their website in our show notes on notion. Please consider joining up to become a member. Thank you for listening to The Idiots Podcast, the UK's premier Infectious Disease podcast. Questions, comments, suggestions. Why don't you send them into Idiots podcasting@gmail.com. Have a five star review in your pocket at Calm, and I would love to have it. Please drop it in your podcast player of choice. And if you want to donate to support the show, there's a link to do so in the description. But until next time, I'm Jane. I'm Callum. See you now. Now that the episode's done, we hope you learn and had lots of fun. So go forth and treat people with some of what you now know.