Fungal Infections and Antifungal Treatments Ringworm Candida Aspergillus Histoplasmosis
Distinguished future physicians welcome toStomp on Step 1 the only free tutorials series that helps you study more efficiently by focusingon the highest yield material. I'm Brian McDaniel and I will be your guide on thisjourney through Fungi. This is the 1st tutorial in my playlist covering all of Microbiologyfor the USMLE Step 1 Medical Board Exam. We are going to review Opportunistic Mycoses,Systemic Mycoses, Superficial Fungal infections and Antifungal medications. This info isn't very high yield for theexam, but I want to give us a little bit of a foundation to build on. Fungi are a groupof eukaryotic organisms that present as either
a unicellular organism (Yeast) or a multicellularorganism (Mold). They are nearly everywhere in nature, but only a small percentage cancause disease in humans. Most of the infections that occur are asymptomatic or so mild thatthat are not detected. Many of the pathogenic Fungi are dimorphic, meaning that they arepresent in the form of a mold in colder temperatures and present in the form of yeast at warmertemperatures (such as body temperature after infecting a human). A way to remember thisis the mnemonic â€œMold in the Cold, Yeast in the Heat.â€� Fungi have a complex reproductivelife cycle that includes formation of Spores which can live in the environment in a vegetativestate. Humans usually contract fungal infections
by acquiring these spores from environmentalsources such as soil. Most fungal infections do not have a person to person spread. Mold form hyphae while Yeast form buddingyeast and psuedohyphae. Both hyphae and Psuedohyphae are branching filamentous vegetative structuresof fungi and each form spores. True hyphae have septae or cell walls between sectionswhile psuedohyphae are formed by budding without a true cell wallseptae between sections. The high yield fungal infections can primarilybe broken down into two groups, Systemic and Opportunistic. Fungi in the systemic categoryhave a higher virulence and can infect health
individuals. While these fungi can infectimmunocompetent individuals the infections are usually mild and localized to the respiratorysystem. In immunocompromised individuals the infections can more commonly spread from thelungs and disseminate to the rest of the body. Systemic fungi are found in specific geographicregions so when a question stem mentions a specific state that should be a buzzword toconsider these fungi. Opportunistic Fungi are lower virulence and have to â€œwait forthe right opportunityâ€� to infect a host. Opportunistic infections usually only occurin immunocompromised patients such as those with AIDs, transplanted organs or cancer.For both systemic and Opportunistic Mycoses
infections the route of infections is mostoften inhalation of a spore from an environmental source. This first leads to a respiratoryinfection, and then given the right circumstances the infection may then spread to other partsof the body. Candida is the exception as it is normal skin flora. We all have Candidapresent on our skin and it only causes a problem when factors lead to an overgrowth of thefungi. The highest yield systemic mycoses are histoplasmosis,blastomycosis Coccidioidomycosis. The highest yield Opportunistic Mycoses are Candida, aspergillus,cryptococcus, mucormycosis Pneumocystis Jiirovecii.
For the most part, these different fungalinfections cannot be differentiated based only on the signs and symptoms. Most of thefungi present like pneumonia with vague flu like symptoms. Therefore, the different fungiare primarily differentiated based on histologic examination of the sputum, biopsy or swab.A stain such as PAS or silver stain is usually needed to visualize the fungi. You shouldbe able to identify the histology of each fungus via a pictures and a text descriptionof the findings as you can be presented with either in the question. Coccidioidomycosis is one of the SystemicMycoses. I give it a high yield rating of