64 BLASTOMYCOSIS (BLASTOMYCES DERMA TITIDIS AND B. GILCHRISTII) Trigger Words Mississippi River Valley, broad-based bud ding yeast, healthy and immunocompro mised, granuloma Biology, Virulence, and Disease ᑏᑏThermally dimorphic fungus: large non encapsulated budding yeast cells in tis sue and in culture at 37° C; mold colonies form in culture at 25° C ᑏᑏUsual route of infection is inhalation of conidia ᑏᑏSeverity of symptoms and course of dis ease depends on extent of exposure and immune status of exposed individual; most are asymptomatic ᑏᑏClassic form of blastomycosis: chronic cutaneous involvement Epidemiology ᑏᑏEcologic niche: decaying organic matter ᑏᑏArea of endemicity: southeastern and southcentral states, especially bordering Ohio and Mississippi river basins; Midwest states and Canadian provinces bordering Great Lakes; and an area in New York and Canada along the St. Lawrence River ᑏᑏOutbreaks of infection have been associ ated with occupational or recreational contact with soil Diagnosis ᑏᑏMicroscopic detection of fungus in tissue or other clinical material, with confirma tion by culture ᑏᑏAntigen detection and PCR Treatment, Prevention, and Control ᑏᑏPulmonary blastomycosis in immunocom promised patients and those with progres sive pulmonary disease should be treated ᑏᑏAll patients with evidence of hematog enous dissemination require antifungal therapy ᑏᑏLipid formulation of amphotericin B: treat ment of choice for meningeal disease and other life-threatening presentations ᑏᑏMild or moderate disease: itraconazole; fluconazole, posaconazole, or voricon azole may be substituted for itraconazole COCCIDIOIDOMYCOSIS (COCCIDIOIDES IMMITIS AND C. POSADASII) Trigger Words Valley fever, coccidioidal granuloma, arthroconidia, spherule, skin test, pre cipitin test Biology, Virulence, and Disease ᑏᑏCoccidioidomycosis caused by two indistinguishable species: C. immitis and C. posadasii ᑏᑏC. immitis is localized to California; C. posadasii causes most infections outside California ᑏᑏDisease caused by inhalation of infectious arthroconidia ᑏᑏAsymptomatic or subclinical, self-limited flulike illness, acute and chronic pul monary disease, single or multisystem dissemination ᑏᑏDimorphic fungi; endosporulating spher ule in tissue, mold in culture at 25° C and in nature Epidemiology ᑏᑏEndemic to U.S. southwestern desert, northern Mexico, scattered areas of Central and South America ᑏᑏOrganism found in soil; growth in environment enhanced by bat and rodent droppings; cycles of drought/rain enhance organism dispersion ᑏᑏPersons ≥65 years and those with HIV infection disproportionately affected ᑏᑏRisk of disseminated disease highest in certain ethnic groups (Filipino, African American, Native American, Hispanic), males (9:1), women in third trimester of pregnancy, individuals with cellular immune deficiency, persons at extremes of age Diagnosis ᑏᑏHistopathologic examination of tissue or other clinical material, isolation of fungus in culture, serology ᑏᑏHistopathologic examination that reveals endosporulating spherules in sputum, exudates, or tissue is sufficient to establish the diagnosis ᑏᑏCulture at 25° C takes days and poses risk to laboratory workers; all work with molds should be performed in suitable biosafety cabinet ᑏᑏSerology (antigen and antibody) may be useful for initial screening, confirmation, or prognostic evaluation Summaries Clinically Significant Organisms Continued 64 • Systemic Mycoses Caused by Dimorphic Fungi 633 The dimorphic fungal pathogens are organisms that exist in a mold form in nature or in the laboratory at 25° C to 30° C and in a yeast or spherule form in tissues or when grown on enriched medium in the laboratory at 37° C (Fig. 64.1). The majority of organisms in this group are considered primary systemic pathogens because of their ability to cause infection in both “normal” and immu nocompromised hosts and for their propensity to involve the deep viscera after dissemination of the fungus from the lungs after its inhalation from nature. The dimorphic systemic pathogens include Blastomyces spp. (B. derma titidis, B. gilchristii, B. helicus, B. parvus, and B. silverae), Coccidioides spp. (C. immitis and C. posadasii), Histoplasma capsulatum var. capsulatum and H. capsulatum var duboisii, Paracoccidioides spp. (P. brasiliensis and P. lutzii), Emergo myces spp. (genus abbreviated Es.; Es. pasteurianus, Es. africanus, Es. orientalis, Es. canadensis, and Es. europaeus), and Talaromyces (formerly Penicillium) marneffei (Table 64.1). These organisms are also known as endemic patho gens, in that their natural habitat is delimited to specific geographic regions (Fig. 64.2), and infection caused by a particular fungus is acquired by inhalation of spores from that specific environment and geographic location (see Table 64.1). H. capsulatum, Coccidioides spp. (C. immitis and C. posadasii), Emergomyces spp. (Es. pasteurianus and Es. africanus), and T. marneffei have emerged as major opportunistic pathogens in individuals with acquired immunodeficiency syndrome (AIDS) and other forms of immunosuppression. Recognition of these endemic myco ses may be complicated by the fact that they may manifest only after the patient has left the area of endemicity. Often, the infection may be quiescent, only to reactivate when the individual becomes immunosuppressed and is living in an area in which the fungus is not endemic. In addi tion to these dimorphic pathogens, agents formerly clas sified under the genus Emmonsia (now obsolete), namely Adiaspiromyces crescens (formerly Emmonsia crescens) and Blastomyces parvus (formerly Emmonsia parva), exist as a filamentous mold in nature at 25° C and as nonreplicating adiaspores in the lungs of animals and humans. Treatment, Prevention, and Control ᑏᑏMost individuals with primary infection do not require therapy ᑏᑏFor those with concurrent risk factors or a more severe presentation: lipid formulation of amphotericin B followed by an oral azole as maintenance therapy (severe disease) ᑏᑏChronic cavitary pulmonary disease: azole for at least 1 year ᑏᑏNonmeningeal extrapulmonary dissemi nated infections: oral azole ᑏᑏMeningeal coccidioidomycosis: fluco nazole; itraconazole, posaconazole or voriconazole are secondary choices HISTOPLASMOSIS (HISTOPLASMA CAPSULATUM) Trigger Words Intracellular yeasts, bird and bat droppings, chicken coop, caves, guano, granulomas Biology, Virulence, and Disease ᑏᑏHistoplasmosis caused by two varieties of H. capsulatum ᑏᑏH. capsulatum var. capsulatum: causes pulmonary and disseminated infections ᑏᑏH. capsulatum var. duboisii: causes pre dominantly skin and bone lesions ᑏᑏDisease caused by inhalation of infectious microconidia ᑏᑏSeverity of symptoms and course of disease depend on extent of exposure and immune status of infected individual; most are asymptomatic, self-limited; flu like illness also occurs ᑏᑏThermally dimorphic fungus: hyaline mold in nature and in culture at 25° C, budding yeast in tissue (intracellular) and in culture at 37° C Epidemiology ᑏᑏH. capsulatum var. capsulatum: localized to Ohio and Mississippi river valleys; occurs throughout Mexico and Central and South America ᑏᑏH. capsulatum var. duboisii: confined to tropical Africa (e.g., Gabon, Uganda, Kenya) ᑏᑏFound in soil with high nitrogen content (e.g., areas contaminated with bird or bat droppings) ᑏᑏOutbreaks of disease have been associated with exposure to bird roosts, caves, and decaying buildings or urban renewal proj ects involving excavation and demolition ᑏᑏImmunocompromised individuals and children most prone to develop symp tomatic disease ᑏᑏReactivation of disease and dissemination common among immunosuppressed individuals, especially those with AIDS Diagnosis ᑏᑏDirect microscopy, culture of clinical material, serology (antigen and antibody), β-d-glucan, and PCR have been useful ᑏᑏYeast phase of organism can be detected in sputum, bronchoalveolar lavage fluid, peripheral blood films, bone marrow, and tissue stained with Giemsa, GMS, or PAS stains ᑏᑏCultures should be handled in a biosafety cabinet ᑏᑏSerologic diagnosis includes tests for antibody and antigen Treatment, Prevention, and Control ᑏᑏSevere acute infections: lipid formula tion of amphotericin B followed by oral itraconazole ᑏᑏChronic pulmonary histoplasmosis: lipid formulation of amphotericin B followed by itraconazole ᑏᑏDisseminated infection: lipid formulation of amphotericin B followed by itraconazole PARACOCCIDIOIDOMYCOSIS (PARACOC CIDIOIDES BRASILIENSIS AND P. LUTZII) Trigger Words Pilot’s wheel, South American blastomyco sis, ulcer, multiple buds Biology, Virulence, and Disease ᑏᑏThermally dimorphic fungus: slowly grow ing mold phase in nature and at 25° C, yeast phase (variable sized with single or multiple buds) in tissue and in culture at 37° C ᑏᑏUsual route of infection is inhalation or possible traumatic inoculation of conidia or hyphal fragments ᑏᑏParacoccidioidomycosis may be subclini cal or progressive with acute or chronic pulmonary forms or acute, subacute, or chronic disseminated forms Epidemiology ᑏᑏEndemic throughout Latin America, areas of high humidity, rich vegetation, moder ate temperatures, acid soil ᑏᑏEcologic niche not well established ᑏᑏOvert disease uncommon among children and adolescents; in adults, disease more common in men aged 30 to 50 years ᑏᑏMost patients with clinically apparent disease live in rural areas and have close contact with soil ᑏᑏNo reports of epidemics or person-to person transmission Diagnosis ᑏᑏDemonstration of characteristic yeast forms on microscopic examination of clinical material: oval to round with dou ble refractile walls and single or multiple buds; “pilot-wheel” morphology ᑏᑏMay be isolated in culture and should be handled in a biosafety cabinet ᑏᑏSerology testing may help in suggesting diagnosis, evaluating response to therapy Treatment, Prevention, and Control ᑏᑏItraconazole: treatment of choice for most forms of disease ᑏᑏMore severe or refractory forms: lipid formulation of amphotericin B followed by either itraconazole or sulfonamide therapy Summaries Clinically Significant Organisms—cont’d GMS, Gomori methenamine silver; PAS, periodic acid-Schiff; PCR, polymerase chain reaction. 634 SECTION 6 • Mycology Saprobic phase (25° Parasitic phase (37° Fig. 64.1 Saprobic and parasitic phases of endemic dimorphic fungi. (A) Histoplasma capsulatum. (B) Blastomyces dermatitidis. (C) Paracoc cidioides brasiliensis. (D) Coccidioides immitis. (E) Talaromyces marneffei. (see Fig. 64.2). The disease is also endemic in other parts of the world, including Africa and parts of Central and South America. MORPHOLOGY As a thermally dimorphic fungus, B. dermatitidis produces nonencapsulated yeastlike cells in tissue and in culture on enriched media at 37° C and white to tan, filamentous, mold colonies on standard mycologic media at 25° C. The mold form produces round to oval or pear-shaped conidia (2 to 10 μm) located on long or short terminal hyphal branches (Fig. 64.3). Older cultures may also produce 7- to 18-μm diameter, thick-walled chlamydospores. This form of B. der matitidis is not diagnostic and may not be distinguishable from the monomorphic Chrysosporium spp. or from an early culture of H. capsulatum. The yeast form of B. dermatitidis is seen in tissue and in culture at 37° C. This form is quite distinctive (Fig. 64.4). The yeast cells are spherical, hyaline, 8 to 15 μm in diam eter, multinucleated, and have thick “double-contoured” walls. The cytoplasm is often retracted from the rigid cell wall as a result of shrinkage during the fixation process. The yeast cells reproduce by the formation of buds or blasto conidia. The buds are usually single and attached to the parent cell by broad bases (see Fig. 64.4). The yeast forms may be visualized in tissue stained with hematoxylin and eosin (H&E); however, the fungal stains, Gomori methenamine silver (GMS) and periodic acid Schiff (PAS), help locate the organisms and delineate their morphology. B. parvus differs from the other species in the genus in that it produces thermally dependent and nonreplicating adiaspores at 37° C and in vivo, rather than yeastlike prop agules, and exhibits a mold phase in nature and at 25° C. The mold phase produces small single-celled conidia (about 4 μm in size) on the sides of the hyphae or on short side branches. Inside the host, the conidia transform into adia spores, which resemble the spherules of Coccidioides species (Fig. 64.1).ᑏ EPIDEMIOLOGY Blastomycosis Blastomycosis is a systemic fungal infection caused by dimorphic pathogens B. dermatitidis and B. gilchristii. Recently additional species of Blastomyces have been pro posed based on molecular taxonomic findings: B. percursus, B. parvus (formerly E. parva), B. helicus (formerly E. helica) and B. silverae. B. percursus, B. helicus, and B. silverae are similar to B. dermatitidis/gilchristii in phenotype and patho genicity. As such, the more familiar B. dermatitidis will be used in this chapter when discussing blastomycosis. B. par vus differs from these species in certain phenotypic aspects and exhibits a distinctly different pathogenesis and will be discussed separately. Like other endemic mycoses, blastomycosis is confined to specific geographic regions, with most infections origi nating in the Mississippi River basin, around the Great Lakes, and in the southeastern region of the United States The ecologic niche of B. dermatitidis appears to be in decay ing organic matter. Studies in humans and animals indicate that infection is acquired after the inhalation of aerosolized conidia produced by the fungus growing in soil and leaf lit ter (Fig. 64.5). Outbreaks of infection have been associated with occupational or recreational contact with soil, and infected individuals include all ages and both genders. A large outbreak

You are an expert medical educator and a professional item writer for University Medical Board Exams and National Licensing Exams (USMLE Step 1/COMLEX Level 1 style). Your task is to generate high-quality multiple-choice questions (MCQs) testing Medical Microbiology with a heavy emphasis on microbial mechanisms. --- CORE FOCUS --- The core subjects are Medical Microbiology (Bacteriology, Virology, Mycology, Parasitology). The exam must place an elevated emphasis on mechanisms: molecular mechanisms of pathogenesis, intracellular vs. extracellular signaling, toxin mechanisms of action (e.g., ADP-ribosylation, cyclic AMP up-regulation), genetic mechanisms of antimicrobial resistance (e.g., plasmids, transposons, altered binding sites), and virulence factors. Stems must be concise and avoid unnecessary narrative fluff. --- QUESTION STYLE & MIX --- The question bank must be a balanced, integrated mix of the following styles: 1. Short, Concise Clinical Vignettes: Punchy case studies presenting key symptoms, exposures, or classic physical signs without wordy filler. 2. Direct/Confusing Diagnostic Puzzles: Questions focusing heavily on differentiating look-alike bugs via laboratory profiles (e.g., catalase, oxidase, hemolysis, growth on selective media, coagulation tests) where options are intentionally tricky or confusing. 3. Pure Mechanistic Questions: Conceptual questions triggered by a very brief clinical context that test the underlying molecular or genetic mechanism of the pathogen or its resistance pattern. Difficulty must be a realistic mix of moderate and hard items. --- QUESTION WRITING RULES (BOARD STANDARDS) --- 1. Every question must provide ALL necessary context within the brief stem. The correct answer must be fully deducible from the provided lab data, clinical clues, or biochemical features. 2. Every question must have exactly FOUR options (A, B, C, D) with only ONE clearly correct answer. 3. Distractors (incorrect options) must be highly plausible, representing microbes that share overlapping lab characteristics, cause similar clinical presentations, or utilize closely related pathogenic mechanisms. Avoid "all of the above" or "none of the above." --- BLOOM'S TAXONOMY DISTRIBUTION (INTERNAL ENGINE ONLY) --- Generate exactly 40 questions. Distribute them across levels using a pyramid structure according to this precise breakdown: - LEVEL 1 (REMEMBERING) & LEVEL 2 (UNDERSTANDING) [~50% of questions / ~20 items]: Focus on direct recognition of classic biochemical profiles, Gram stain morphology, or the direct biochemical target of a specific bacterial toxin. - LEVEL 3 (APPLYING) [~35% of questions / ~14 items]: Require identifying the most likely pathogen or mechanism when given a short clinical scenario or mixed laboratory findings. - LEVEL 4 (ANALYZING) & LEVEL 5 (EVALUATING) [~15% of questions / ~6 items total]: Harder, multi-step questions. For example, predicting resistance profiles based on gene transfer descriptions, or analyzing atypical host-pathogen interactions and virulence mutations. Do NOT label, state, or mention these levels anywhere in your response. --- CRITICAL OUTPUT FORMATTING RULES --- - Do NOT include any question titles, headers, or section names. - Do NOT label, state, or indicate anywhere what specific organism or concept a question is testing. - Do NOT state, mention, or reveal what Bloom's Taxonomy level the question belongs to. - Present the questions as a clean, consecutive, numbered list from Question 1 through Question 40. For each question, provide ONLY: 1. The Clinical Vignette / Technical Stem 2. Options A, B, C, D 3. The Correct Answer Letter 4. A Detailed Explanation/Rationale explaining why the correct option is the definitive answer based on the microbiological and mechanistic data, and exactly why each distractor is incorrect.