Zygomycosis and the Joplin Tornado
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Published: July 2011Print Record of Viewing
Following in the wake of the EF5 tornado that struck Joplin, Missouri in May of 2011, there has been an outbreak of life-threatening fungal infections among people in the area. Identifying the source of the infections and how the people were exposed yields some surprising answers.
Presenter: Glenn D. Roberts, PhD
- Professor of Laboratory Medicine and Pathology, and Microbiology
- Consultant in the Division of Clinical Microbiology at Mayo Clinic in Rochester, Minnesota
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Our presenter for this program is Dr. Glenn Roberts, Professor of Laboratory Medicine and Pathology, and Microbiology, as well as a consultant in the Division of Clinical Microbiology at Mayo Clinic in Rochester, Minnesota. Dr. Roberts discusses the development of life-threatening fungal infections in the citizens of Joplin, Missouri, following the EF5 tornado that stuck in May of 2011. Identifying the source of the infections and how the people were exposed yields some surprising answers. Thank you, Dr. Roberts.
Tragedy in Joplin
I think many of us watched on a Sunday afternoon, late in the afternoon, the coverage by the weather channel about the tragedy in Joplin, Missouri where an EF 5 tornado struck the city on that day, May 22, 2011. It was a terrible tragedy. As of June 24, there were 156 people who died as a result of that tornado. There were over 1100 people that were hospitalized and about 30-50 % of the city was destroyed beyond repair. One of the scenes that was shown by the weather channel was the St. John’s hospital. It was so badly damaged that it was condemned and all patients were transferred to other hospitals in the area, actually, within a four state region and there were 183 patients in that hospital. Two patients were lost as a result of the tornado and the rest of them were moved out of the hospital within 90 minutes by the hospital staff. So the hospital was well prepared for a storm like this. They had practiced the drills many times. There were many makeshift treatment stations set up within the city to handle the acute care from all of the people who were injured by the flying debris in the tornado. Many things happened as a result of that tornado. But one of the things that were unsuspected was the appearance of a fungal infection that seemed to infect a number of Joplin residents. And that is a common fungal infection that is not seen very often at all except in transplant patients or people who are immunosuppressed.
Unsuspected Fungal Infection Infects Some Joplin Residents
But in this case, there were twelve patients who ended up having zygomycosis as a result of being hit by flying debris from this storm that hurled metal, wood, all sorts of materials at a speed of over 200 miles per hour and implanted those particular objects into the skin. As a result, these people developed cutaneous zygomycosis. And three persons have died now and it has not been determined for sure if they have died as a result of the zygomycosis infection or from the tornado or from something else.
Zygomycosis is a term you see on the slide as a heading but a lot of people like to use the term mucormycosis. That is an old term that seems to be revived now but zygomycosis is caused by a number of different fungi and they all belong to the group zygomycetes. For example, Mucor, Rhizopus, Lichtheimia which is one you are probably not familiar with, it’s a new term for Absidia and Apophysomyces and some others, many other fungi. These organisms are found as part of the normal flora in the environment. They are found in decaying wood and vegetation leaves, all kinds of plant material that is decomposing and in the case of the Joplin tornado; these organisms were in the environment and spread in the tornado. They were actually uplifted from the soil by the wind velocity and taken around all over the city of Joplin. We think of zygomycosis, the first thing we think about is rhinocerebral disease for the nose, the sinuses and eventually the brain and the orbital sinuses become involved. That occurs primarily in immunocompromised hosts, in particular, the diabetic with acute state of ketoacidosis. And brain abscess also is a consequent of that same type of infection. Pulmonary infection occurs in immunocompromised hosts, transplant patients, and so on. Gastrointestinal disease occurs and disseminated disease occurs particularly in transplant patients. Localized soft tissue infection happens and down below on the right hand side, you can see this happens to be the leg of someone who ended up getting zygomycosis and if you look close you can see the tendons that are actually growing mold on the surface of the tendons and this is the type of situation that is probably occurring in the Joplin infection.
Zygomycetes are a group of fungi that are characterized by a number of things. One is that they have rather large hyphae that are nonseptate. We call them pauciseptate because they produce occasional septations and they may have those or they may not have them depending on the organism and how old it is. But also, we know that these zygomycetes produce asexual spores inside of a saclike structure called a sporangium. And the sporangium is located at the tip of a long supporting structure called a sporangiophore. You don’t see that with any other fungi. Consequently, we call these zygomycetes by a certain group name because they have these features. But they are characterized in the literature by having zygospores as a result of sexual reproduction. And the term zygomycosis comes from the fact they can produce zygospores even though you really don’t see these in the clinical laboratory very often, almost never. So the term zygomycosis is used, certainly by me and by many others but others have decided to use the term mucormycosis and that is fine. One of the hallmarks of these infections caused by the zygomycetes is a marked propensity for vascular invasion. And these organisms can penetrate a vessel in a matter of a few hours and cause total occlusion of that vessel based on the fact that platelets, red cells and white cells, aggregate within that vessel and cause a thrombus to form and then the blood flow is prevented from going distal to that. And what happens is, the tissue all downstream becomes necrotic and dies and this is the hallmark of zygomycosis is the dead tissue that actually turns black and you look in sinuses for example, and see black eschar because of all this tissue and destruction and necrosis. One of the things in the case of the Joplin situation is they are able to debride some of those areas where the tissue has become involved.
The zygomycetes again have another hallmark feature. And that is that they grow very quickly in culture just like they grow inside of a vessel. They are grown in a matter of a few hours and we have a term that we use called lid lifter, and if we planted a culture today and came in tomorrow morning, the lid would actually be pushed up by this organism because its growth rate is so quickly and the organism grows at an upward and it will lift the lid. So we call them lid lifters. As we see the culture mature, the sporangia, these saclike structures form and they become dark.You will notice that the plate will become mottled with black dots and those are the sporangia.
This is an image of pauciseptate hyphae. Actually, these hyphae are not pauciseptate at all, these are a nonseptate. There are no septations in there that I can see and this is something you see with zygomycetes but then as you look further around you will find there are some hyphaes sometimes with septate in there and I will show you those shortly.
Zygomycetes: Basic Structures
Zygomycetes have the basic structure which we mentioned and you can see them on this diagram so it will make it a little easier for us to recognize them in the illustrations that we are going to see. The large saclike structures are the sporangia. Within the sporangium would be the sporangiophore. And down below the sporangium in the sac like structure going toward the bottom is the supporting structure called the sporangiophore. And notice down below there are some root-like structures called rhizoids. These rhizoids anchor the culture to the substrate in which the organism is growing. They are not present with all cultures but they are used as a means for us to identify the genus of some of these organisms because we can characterize the fungi with the basis of whether or not they have rhizoids or if they do have them, how they are positioned. Another structure that is shown on here is the Columella. The Columella is a bulbous swelling that is inside the sporangium and you can see that sometimes if the sporangium has been ruptured. So we will look and see if we can find that as we go along here.
Now, these are examples of the structures we just talked about. The sporangia you see on the right of the sac like structures. The curved structure in this particular illustration is the sporangiophore. The sporangiophore supports the sporangium which contains all of those sporangiospores. And a mature sporangia will actually rupture the wall and dissolve and all those spores go out into environment and start to form new structures all over again. The rhizoids we mentioned are the root like structures that are helpful in making this genus identification and you can see that on the lower illustration.
One of those organisms that we see very commonly is Rhizopus. These organisms Rhizopus, Mucor, and the others are not always pathogenic. They are not pathogenic unless the circumstances are just right. They belong to a group of fungi called the opportunistic infections. And that means that everything happens to be just right for these organisms to infect the patient. The patient has to be immunosuppressed and so on or something unusual has to happen just like it did with the Joplin tornado. With Rhizopus you will notice that the rhizoids are facing downward and if you trace the sporangiophore up towards the sporangium, you will see that the rhizoids are produced right at the base of that sporangiophore. And that is the hallmark of Rhizopus is that the rhizoids are produced right at the base of the sporangium and within the sporangium would be the columella and in this you cannot see that but when the sporangiospores are out of there you can see that is looks like an umbrella.
Lichtheimia (Absidia) Species
Lichtheimia (Absidia) produces rhizoids and it produces them in a different way. And this is what we mentioned before is that the rhizoids if they are there help us to identify the genus. If you notice on this illustration, on the larger one, you will see the two sporangia on the top of the sporangiophore and if you follow it down to the bottom, you will notice that the rhizoids at the left are very far apart from the sporangiophore. They are produced away from the sporangiophore and that is what you see with Lichtheimia. Another thing that is shown here in the smaller illustration is that below this sporangium is a funnel-like structure called an apophysis and you see that with Lichtheimia.
And you can see on this illustration, this is Lichtheimia and it has these pear shaped sporangia with that funnel-like apophysis at the base. And if you follow it down just a little ways you can see there is septum in the sporangiophore that is obvious and has the characteristic of this organism.
Mucor is one that does not produce rhizoids at all and only produces sporangiophores and sporangias. That is the hallmark of Mucor and it is one that is fairly easy to recognize because of the lack of rhizoids.
Cunninghamella is one that you don’t see all that often but it does cause disease particularly in burn patients. It is characterized by having sporangium and at the tip a swollen vesicle that gives rise to the sporangiola. These are sporangia that are sitting on the outside of a vesicle and they are attached to that vesicle by a thread-like attachment. And those sporangiola have very fine spikes on them. And you can’t see them on this illustration but if you see it underneath a microscope at a higher power, you will notice they are very finely rough walled. This organism does cause disease in burn patients. Cunninghamella elegans.
Another one is Apophysomyces elegans. This is an organism that is not seen all that often but it does cause disease acquired by trauma. And it is an organism that gives rise to pear shaped sporangia just like Lichtheimia. It has an apophysis that is very prominent. It looks like a cocktail glass down below. And this happens to be the organism that has been found in the patients in Joplin, is Apophysomyces, a very unusual finding.
This is a culture of Apophysomyces that has probably been growing for maybe 12 hours and you can see that the culture plate is full. If you notice around the edge, you will see that it is growing out from under the lid and it is growing on the outside of the culture dish. This is what we were talking about with the rapid growth and the lid lifter.
This is Apophysomyces and you can see the cocktail glass appearance because of that pronounced apophysis. Apophysomyces also has rhizoids which are not shown on any of the illustrations I have here and they are produced in about the same place that you see with Lichtheimia. So once you see Apophysomyces you have to sort it out from Lichtheimia. Notice that the sporangiospores here are elongated, which is not what you see with most of the zygomycetes.
Here is a very good one showing you the apophysis and follow it down, follow the sporangiospore, follow all the way down to the bottom and you notice there is a cell that looks like a foot. It is called a foot cell and that also is a hallmark of Apophysomyces.
This is just another illustration to show you. This is an unusual organism. We have seen a case or two of Apophysomyces and sometimes it is not so easy to identify.
Diagnosis of Zygomycosis
Well, the clinical diagnosis of Zygomycosis is based on a number of things. One are the clinical signs, obvious what kinds of diseases it causes and what the clinician suspects. A biopsy is probably the preferred means of making a diagnosis because it needs to come from a sterile sight and you need to see tissue invasion by pauciseptate hyphae. You can do a direct microscopic examination of sterile material if you get an abscess or something that you know is sterile and you happen to see those hyphae in there that is fine to be able to recognize those hyphae in there, those pauciseptate hyphae. We do have PCR for rapid detection of some of the Zygomycetes that cannot separate all of those but is available. And then we also have means to identify some of these unusual Zygomycetes by nucleic acid sequencing. And Apophysomyces can be identified by nucleic acid sequencing as well as by morphology.
Large Pauciseptate Hyphae—H&E Stain
This is an example of what you would see in a biopsy. This is an H&E stained slide that you would look at for tissue morphology but in this case, you see where the arrow is, there are large hyphae that are present in there that really show very little evidence of septations. Although, you can see a couple of areas where there are septations. And this is what is called pauciseptate hyphae. There are not regular septations throughout the whole length of the hyphal strand and a lot of times these Zygomycetes have fractured pieces of hyphae within the tissue rather than very long pieces.
Unstained Hyphal Fragment On GMS-Stained Tissue
This is Gomori methanamine silver stain which we use for staining fungi. It does not stain the zygomycetes very often and the stainings preparation we use here at Mayo Clinic. And we have used that for years as a means to be able to sort out the zygomycetes from other fungi.
Vascular Invasion By Hyphae
You can see here this is a vessel that has been invaded by a zygomycetes. The whole vascular wall is surrounded by a zygomycetes. And as we mentioned earlier, what happens is they hyphae grow down inside the vessel, the red cells, the white cells plate aggregate on that and form a clot or a thrombus and it blocks or occludes the artery and then the blood supply down to that area distally, does not occur and so the tissue dies and becomes necrotic and that is where the major problem occurs.
Large Pauciseptate Hyphae—Calcofluor White
This is calcofluor white stain that we use for looking at clinical specimens underneath the microscope for direct exam. And this happens to be hyphae of a zygomycetes fluorescing blue-white with calcofluor white. Calcofluor white is a fluorescent brightener that is found in textiles to make them whiter. And someone found out that when combined with fungi and under fluorescent microscopy will fluoresce this color or another color depending on the filters that you use but in this situation, you can see the hyphae that are very long and they branch at right angles and not at forty five degree angles and there may be a few septations in there but predominately it is non-septate.
I would like to extend my sympathy from all of us at Mayo Clinic to the people of Joplin for their loss and for all of the grief they have experienced throughout this whole time with this tornado. You have some very good clinicians and staff over to help you deal with this problem and we wish you the best of luck.