Sporotrichosis – Subcutaneous, Cutaneous and Superficial Mycoses

00:00 The first we will talk about is Sporotrichosis, and this is an infection caused by Sporothrix schenckii, which like many of the fungi we've been discussing, is a dimorphic fungus. It can alternate between filamentous forms which you can see on the right and yeast or single cell forms on the left. Come to think of it, can you name one of the fungi that we've talked about which is not dimorphic? I’ll give you a few seconds. If you said Saccharomyces cerevisiae, you’d be right. Sporothrix schenckii, this is a mold in the environment.

00:47 It’s an environmental fungus, it grows, is hyphae and mycelia, this produces spores of course, to produce more organisms in the wild and it is the spores that are infectious. Interestingly for the Sporotrichosis organism, it is temperature that causes the change in the body form.

01:09 So at high temperatures, the temperature of the human body, 37 Celsius or 98 Fahrenheit, this causes the fungus to assume the yeast form. Normally in the environment it prefers to grow at lower temperatures at which it grows in the mycelia forms. This fungus is present in soil, it's present in moss, decaying wood, vegetation, throughout the world.It's everywhere.

01:37 It's ubiquitous as we say, and it's an environmental fungus, very much like the other ones that we've talked about. Acquisition of the disease, Sporotrichosis, is mostly associated with people who work outdoors or with people who have jobs involving farming, landscaping, and gardening. Typically what happens is that your hands are dirty and you've encountered some of this fungus on your hands and then you injure the hand and introduce the fungus into deeper cell layers. So we inoculate the spores of the fungus into the dermis or the subcutaneous tissues, for example, by a thorn on a rose, splinters from wood or any sharp vegetation or even maybe your farming tool cuts your hand or your arm and you push the spores deep into your skin. So what is the moral of this story? When you work outside you should wear gloves of course, just like you should wear a mask when you are destroying old buildings to prevent inhaling spores, but most people do not, maybe everyone needs to listen to my lectures, and that's the solution. So, most of the infections occur on your hands and arms, most sporotrichosis that we see. More rarely, people can inhale the spores and this causes what's called pulmonary sporotrichosis, but this is quite rare. Most of the time these spores are inoculated into the skin causing the skin disease. And the incubation time is long, it takes a few weeks, but you will eventually see a single nodular lesion on the site on your hands or your arm, wherever you have inoculated the spores into. And in some patients these multiply, and the idea is that the organism, the yeast form of the organism, which we assumed inside of you, travels through the lymph system. You know as things enter us, they are filtered into the lymph system, which has access to every part of our body. So it is thought that these cells spread up and down on your arm via the lymph system, so you get multiple nodules and these are red raised nodules on your skin.

04:01 So here's a picture of a typical case of sporotrichosis, this probably began as an initial nodule on the skin from the site of the initial injury and now it's spread as the yeast form is spreading throughout the arm via the lymphatics. Now, what do you think happens in an immunosuppressed individual? That's correct, they will have even more extensive spread and these yeasts may even invade your organs, we call that the visceral infection by systemic spread, and that can be life-threatening. So if you are immunosuppressed in any way and you like gardening, the two are not exclusive, you should wear gloves and be very careful. How do you diagnosis this? You can do a biopsy of these lesions and either a try and culture the organism or look at it under the microscope, do histopathology, it will show the typical granulomatous inflammation, that is encapsulated organisms with signs of inflammation in the tissues. And this can be treated with itraconazole.