Lecture 15 New PDF

Lecture 15 Mycosis Aspergillus, Aspergillosis Aspergillosis is a spectrum of diseases that may be caused by a number of Aspergillus species. Aspergillus species are ubiquitous saprobes in nature, and aspergillosis occurs worldwide. A fumigatus is the most common human pathogen, but many oth...

Lecture 15 Mycosis Aspergillus, Aspergillosis Aspergillosis is a spectrum of diseases that may be caused by a number of Aspergillus species. Aspergillus species are ubiquitous saprobes in nature, and aspergillosis occurs worldwide. A fumigatus is the most common human pathogen, but many others, including A flavus, A niger, and A terreus, may cause disease Aspergillus (2) This mold produces abundant small conidia that are easily aerosolized. Following inhalation of these conidia, atopic individuals often develop severe allergic reactions to the conidial antigens. In immunocompromised patients—especially those with leukemia, stem cell transplant patients, and individuals taking corticosteroids— the conidia may germinate to produce hyphae that invade the lungs and other tissues. Morphology and Identification Aspergillus species grow rapidly, producing aerial hyphae that bear characteristic conidial structures: long conidiophores with terminal vesicles on which phialides produce basipetal chains of conidia. Conidia The species are identified according to morphologic differences in the these structures, Conidiosphore including the size, shape, texture, and color of the conidia. Morphology and Identification (2) Aspergillus species are rapidly growing molds with branching septate hyphae and characteristic arrangement of conidia and conidiosphore. Fluffy colonies appear in 1-2 days, by 5th day they may cover an entire plate with pigmented growth. Species are identified on the basis of differences in the structure of the conidiosphore and the arrangement of conidia. Aspergillus fumigatus Morphology and Identification (3) Species are identified on the basis of differences in the structure of the conidiosphore and the arrangement of conidia. Pathogenesis In the lungs, alveolar macrophages are able to engulf and destroy the conidia. However, macrophages from corticosteroid-treated animals or immunocompromised patients have a diminished ability to contain the inoculum. In the lung, conidia swell and germinate to produce hyphae that have a tendency to invade preexisting cavities (aspergilloma or fungus ball) or blood vessels. Pathogenesis (2) Adherence is associated with the ability of Aspergillus conidial proteins to bind fibrinogen and laminin. Disease progression has been related to specific Aspergillus glucans and galactomannans. Gliotoxin, a molecule that inhibits steps of oxidative killing mechanisms of phagocytes, may also assist progression. The virulent species produce extracellular elastases, proteinases and phospholipases. The ability of Aspergillus to form biofilms has been implicated in infections developing in medical devices and implants.  Manifestation Aspergillus may cause clinical allergies or occasional invasive infection. In both cases the lung is the organ primerely involved. Allergic disease is marked by eosionophilia and specific IgG. Invasive aspergilosis occurs in the settings of preexisting pulmonary disease (e.g. tuberculosis, asthma) or immunodepression. Aspergillus can lead to invasion into the tissue by branching septate hyphae. In patients who already have a chronic pulmonary disease , mycelial masses can form a radiologically visible fungus ball (aspergilloma) within the preexisting cavity. Lung tissue invasion may penetrate blood vessels causing hemoptyses or erosion into other structures with development of fistulas. Invasive disease outside lungs is rare unless patients are immunoocompromised. Pneumonia in immnocompromised host has a grave prognosis. Clinical findings A. Allergic forms In some atopic individuals, development of IgE antibodies to the surface antigens of aspergillus conidia elicits an immediate asthmatic reaction upon subsequent exposure. In others, the conidia germinate and hyphae colonize the bronchial tree without invading the lung parenchyma. This phenomenon is characteristic of allergic bronchopulmonary aspergillosis, which is clinically defined as asthma, recurrent chest infiltrates, eosinophilia, and both type I (immediate) and type III (Arthus) skin test hypersensitivity to Aspergillus antigen. Many patients produce sputum with Aspergillus and serum precipitins. They have difficulty breathing and may develop permanent lung scarring. Normal hosts exposed to massive doses of conidia can develop extrinsic allergic alveolitis Allergic bronchopulmonary aspergilosis B. ASPERGILLOMA AND EXTRAPULMONARY COLONIZATION Aspergilloma occurs when inhaled conidia enter an existing cavity, germinate, and produce abundant hyphae in the abnormal pulmonary space. Patients with previous cavitary disease (eg, tuberculosis, sarcoidosis, emphysema) are at risk. Some patients are asymptomatic; others develop cough, dyspnea, weight loss, fatigue, and hemoptysis. Cases of aspergilloma rarely become invasive. Localized, noninvasive infections (colonization) by Aspergillus species may involve the nasal sinuses, the ear canal, the cornea, or the nails. Aspergilloma Computed tomography scan of the X-ray image thorax showing a cavitary lesion in the upper lobe of left lung containing an aspergilloma Invasive aspergillosis Following inhalation and germination of the conidia, invasive disease develops as an acute pneumonic process with or without dissemination. Patients at risk are those with lymphocytic or myelogenous leukemia and lymphoma, stem cell transplant recipients, and especially individuals taking corticosteroids. Symptoms include fever, cough, dyspnea, and hemoptysis. Hyphae invade the lumens and walls of blood vessels, causing thrombosis, infarction, and necrosis. From the lungs, the disease may spread to the gastrointestinal tract, kidney, liver, brain, or other organs, producing abscesses and necrotic lesions. Without rapid treatment, the prognosis for patients with invasive aspergillosis is grave. Persons with less compromising underlying disease may develop chronic necrotizing pulmonary aspergillosis, which is a milder disease. Abdominal aspergillosis Abdominal aspergillosis involving the liver, spleen, and kidney in a 30-year-old woman who received chemotherapy for acute myeloid leukemia. (A and B) Contrast-enhanced axial CT scans show a pseudoaneurysm of the splenic artery (arrow) with diffuse low-attenuating lesions and cortical enhancing rim, representing infarction in the spleen as well as multiple tiny low-attenuating lesions in the liver and both kidneys (arrowheads). Laboratory Diagnosis SPECIMENS Sputum, other respiratory tract specimens, and lung biopsy tissue provide good specimens. Blood samples are rarely positive. MICROSCOPIC EXAMINATION On direct examination of sputum with KOH or calcofluor white or in histologic sections, the hyphae of Aspergillus species are hyaline, septate, and uniform in width (about 4 µm) and branch dichotomously. Laboratory Diagnosis (2) CULTURE Aspergillus species grow within a few days on most media at room temperature. Species are identified according to the morphology of their conidial structures. SEROLOGY The ID test for precipitins to A fumigatus is positive in over 80% of patients with aspergilloma or allergic forms of aspergillosis, but antibody tests are not helpful in the diagnosis of invasive aspergillosis. However, a serologic test for circulating cell wall galactomannan is diagnostic. Treatment Aspergilloma is treated with itraconazole or amphotericin B and surgery. Invasive aspergillosis requires rapid administration of either the native or lipid formulation of amphotericin B or voriconazole, often supplemented with cytokine immunotherapy. Allergic forms of aspergillosis are treated with corticosteroids or disodium chromoglycate. Immunity The efficiency of innate immune mechanisms is the most probable reason that Aspergillus infection is extremely rare in healthy people. Alveolar macrophages kill conidia and PMN attack hyphae.  Epidemiology Aspergillus species are widely distributed in nature and found throughout the world. Inhalation of Aspergillus spores is the mode of infection. Conidia may be spread through the air ducts. Aspergillus fumigatus was the initial agents identified in 2012 as the cause of widespread series of meningitis cases traced to contaminated steroid medication injected into CSF. Control For persons at risk for allergic disease or invasive aspergillosis, efforts are made to avoid exposure to the conidia of Aspergillus species. Most bone marrow transplant units employ filtered air-conditioning systems, monitor airborne contaminants in patients’ rooms, reduce visiting, and institute other measures to isolate patients and minimize their risk of exposure to the conidia of aspergillus and other molds. Some patients at risk for invasive aspergillosis are given prophylactic lowdose amphotericin B or itraconazole  Zygomycetes and zygomycosis Mucormycosis (zygomycosis) is an Absidia Rhizopus opportunistic mycosis caused by a number of molds classified in the order Mucorales of the phylum Zygomycota. Zygomycosis (mucoromycosis) is the term applied to infection with any of the group of zygomycetes, the most common of which are: Absidia, Rhizopus, Cunninghamella, and Mucor – soil saprophytes. The conditions that place patients at risk include acidosis—especially that associated with diabetes mellitus—leukemias, lymphoma, corticosteroid treatment, severe burns, immunodeficiencies, and other debilitating Cunninghamella Mucor diseases as well as dialysis with the iron chelator deferoxamine. Pulmonary disease is similar to that from other fungi. Rhinocerebral mycosis The major clinical form is rhinocerebral mucormycosis, which results from germination of the sporangiospores in the nasal passages and invasion of the hyphae into the blood vessels, causing thrombosis, infarction, and necrosis. The disease can progress rapidly with invasion of the sinuses, eyes, cranial bones, and brain. Blood vessels and nerves are damaged, and patients develop edema of the involved facial area, a bloody nasal exudate, and orbital cellulitis. The rhinocerebral form produces slow the dramatic clinical syndrom: The clinical syndrom begins with the headache and may progress through orbital cellulitis and hemorrhage to cranial nerve palsy, vascular thrombosis, coma and death in less than 2 weeks. Rhinocerebral mucoromycosis Thoracic mucormycosis Thoracic mucormycosis follows inhalation of the sporangiospores with invasion of the lung parenchyma and vasculature. In both locations, ischemic necrosis causes massive tissue destruction. Less frequently, this process has been associated with contaminated wound dressings and other situations. Plain radiograph of chest posteroanterior view shows loculated right hydropneumothorax (red arrow) with collapsed lung (white arrow) Identification Direct examination or culture of nasal discharge, tissue, or sputum will reveal broad hyphae (10–15 µm) with uneven thickness, irregular branching, and sparse septations. These fungi grow rapidly on laboratory media, producing abundant cottony colonies. Identification on the sporangial structures. TREATMENT consists of aggressive surgical debridement, rapid administration of amphotericin B, and control of the underlying disease. Many patients survive, but there may be residual effects such as partial facial paralysis or loss of an eye. Pneumocystis jiroveci Pneumocystis jiroveci causes pneumonia in immunocompromised patients; dissemination is rare. Until recently, P jiroveci was thought to be a protozoan, but molecular biologic studies have proved that it is a fungus with a close relationship to ascomycetes. Pneumocystis species are present in the lungs of many animals (rats, mice, dogs, cats, ferrets, rabbits) but rarely cause disease unless the host is immunosuppressed. P jiroveci is the human species, and the more familiar P carinii is found only in rats. Pneumocystis jirovecii Prior to the introduction of effective chemoprophylactic regimens, it was a major cause of death among AIDS patients. Chemoprophylaxis has resulted in a dramatic decrease in the incidence of pneumonia, but infections are increasing in other organs, primarily the spleen, lymph nodes, and bone marrow. Pneumocystis jirovecii P jiroveci has morphologically distinct forms: thin-walled trophozoites and cysts, which are thick-walled, spherical to elliptical (4–6 µm), and contain four to eight nuclei. Cysts can be stained with silver stain, toluidine blue, and calcofluor white. In most clinical specimens, the trophozoites and cysts are present in a tight mass that probably reflects their mode of growth in the host. P jiroveci contains a surface glycoprotein that can be detected in sera from acutely ill or normal individuals.  Pneumocystis Pneumocystis jirovecii is the cause of lethal pneumonia in immunocompromised persons particularly with AIDS. P jiroveci is an extracellular pathogen. The organism has not been grown in culture and was long considered a parasitic based on morphology of forms seen in infected tissue. Growth in the lung is limited to the surfactant layer above alveolar epithelium. The observed stages of Pneumocystis live cycle include the stages called: trophic, precyst and cyst. No filamentous forms have been observed. Charateristic of Pneumocystis The trophyc form is bound to a cell wall and cytoplasmic membrane that enclose nucleus and mitochondria. As precyst matures, the nuclei divide to form 8 “spores” within the original structure to form the cyst. The spores have eccenric nucleus, a nucleus and a single mitochondrion in cytoplasm. The cell wall lacks the rigidity typical to fungi, however the biochemical elements of the fungal cell wall are present (N- acetylglucosamine, the primary subunit of chitin and major surface glycoprotein (Msg) has been identified. The dominant sterol of the cythomplasmic membrane is cholesterol, rather than ergosterol characteristic of fungi. Current insights into the biology and pathogenesis of Pneumocystis pneumonia Manifestation Pneumocystis pneumonia is insidious beginning with mild fever or malaise is persons whose immune system is compromised. Signs referred to lung come later with nonproductive cough, shortness of breath, progressive cyanosis, hypoxia and asphyxia can lead to death in 3-4 weeks period. Lesion outside lungs were rarely seen before AIDS epidemic, but now appear with some regularity. The sites most often invade lymph nodes, bone marrow, spleen, liver, eyes, thyroid, adrenal glands, gastrointestinal tract, and kidneys. Epidemiology Worldwide distribution in humans and animals. Antibodies are common. Airborne transmission is probable. Pneumocystis pneuminia (PCP) is a complication of immuniodeficint state. AIDS patients are at high risk. Pathogenesis Pneumocystis is an organism of low virulence, which seldom produces disease in a host with normal T-lymphocytes function. Major surface glycoprotein (Msg) abundant on the surface of Pneumocystis jirovecii may act as attachment ligand to several host proteins, including fibronectin, vitronectin and surfctant proteins. Hystologically, Pneumocystis pneuminia (PCP) is characterized by alveoli filled with foamy excudate. Diagnosis Specimens:  bronchoalveolar lavage,  lung biopsy tissue,  sputum Staining:  Giemsa,  toluidine blue,  methenamine silver,  calcofluor white Examination: Presence of cysts or trophozoites. A specific monoclonal antibody is available for direct fluorescent examination of specimens. Immunity, Treatment and Prophylaxis Cell-mediated immunity presumably plays a dominant role in resistance to disease. TREATMENT Acute cases of pneumocystis pneumonia are treated with trimethoprim-sulfamethoxazole or pentamidine isethionate. PROPHYLAXIS can be achieved with daily TMP-SMZ or aerosolized pentamidine. Other drugs are also available. Epidemiology No natural reservoir has been demonstrated, and the agent may be an obligate member of the normal flora. Persons at risk are provided with chemoprophylaxis. The mode of infection is unclear, and transmission by aerosols may be possible. Other opportunistic mycoses Individuals with compromised host defenses are susceptible to infections by many of the thousands of saprobic molds that exist in nature and produce airborne spores. Such opportunistic mycoses occur less frequently than candidiasis, aspergillosis, and mucormycosis because the fungi are less pathogenic. Advances in medicine have resulted in growing numbers of severely compromised patients in whom normally nonpathogenic fungi may become opportunistic pathogens. Devastating systemic infections have been caused by species of Fusarium, Paecilomyces, Bipolaris, Curvularia, Alternaria, and many others. Some opportunists are geographically restricted. For example, AIDS patients in Asia acquire systemic infections with Penicillium marneffei, which is a dimorphic pathogen endemic to the area. Another contributing factor is the increasing use of antifungal antibiotics, which has led to the selection of resistant fungal species and strains Antifungal prophylaxis Opportunistic mycoses are increasing among immunocompromised patients, especially in patients with hematological dyscrasias (eg, leukemia), hematopoietic stem cell recipients, and solid organ transplant patients, and others receiving cytotoxic and immunosuppressive drugs (eg, corticosteroids). There is no universal consensus on the criteria for administering antifungal prophylaxis. Most hospitals use oral fluconazole; others prescribe a short course of low-dose amphotericin B. Antifungal chemotherapy There are a limited but increasing number of antibiotics that can be used to treat mycotic infections. Most have one or more limitations, such as profound side effects, a narrow antifungal spectrum, poor penetration of certain tissues, and the selection of resistant fungi. Promising new drugs are currently under development, and others are being evaluated in clinical trials. Finding suitable fungal targets is difficult because fungi, like humans, are eukaryotes. Many of the cellular and molecular processes are similar, and there is often extensive homology among the genes and proteins. Mechanisms of action of antifungal drugs The classes of currently available drugs include the polyenes (amphotericin B and nystatin), which bind to ergosterol in the cell membrane; flucytosine, a pyrimidine analog; The azoles and other inhibitors of ergosterol synthesis, such as the allylamines; The echinocandins inhibit the synthesis of cell wall β-glucan. Griseofulvin interferes with microtubule assembly. Currently under investigation are inhibitors of cell wall synthesis, such as nikkomycin and pradimicin, and sordarin, which inhibits elongation factor 2. Amphotericin B Amphotericin B is the most effective drug for severe systemic mycoses. It has a broad spectrum, and the development of resistance is rare. The mechanism of action of the polyenes involves the formation of complexes with ergosterol in fungal cell membranes, resulting in membrane damage and leakage. Amphotericin B has greater affinity for ergosterol than cholesterol, the predominant sterol in mammalian cell membranes. Mechanism of action Amphotericin B firmly binds to ergosterol in the cell membrane. This interaction alters the membrane fluidity and perhaps produces pores in the membrane through which ions and small molecules are lost. Unlike most other antifungals, amphotericin B is cidal. Mammalian cells lack ergosterol and are relatively resistant to these actions. Amphotericin B binds weakly to the cholesterol in mammalian membranes, and this interaction may explain its toxicity. At low levels, amphotericin B has an immunostimulatory effect. Indications Amphotericin B has a broad spectrum with demonstrated efficacy against most of the major systemic mycoses, including coccidioidomycosis, blastomycosis, histoplasmosis, sporotrichosis, cryptococcosis, aspergillosis, mucormycosis, and candidiasis. The response to amphotericin B is influenced by the dose and rate of administration, the site of the mycotic infection, the immune status of the patient, and the inherent susceptibility of the pathogen. Penetration of the joints and the central nervous system is poor, and intrathecal or intraarticular administration is recommended for some infections. Amphotericin B is used in combination with flucytosine to treat cryptococcosis. Side effects All patients have adverse reactions to amphotericin B, though these are greatly diminished with the new lipid preparations. Acute reactions that usually accompany the intravenous administration of amphotericin B include fever, chills, dyspnea, and hypotension. These effects can usually be alleviated by prior or concomitant administration of hydrocortisone or acetaminophen. Tolerance to the acute side effects develops during therapy. Chronic side effects are usually the result of nephrotoxicity. Hypokalemia, anemia, renal tubular acidosis, headache, nausea, and vomiting are frequently observed. Flucytosine Flucytosine (5-fluorocytosine) is a fluorinated derivative of cytosine. It is an oral antifungal compound used primarily in conjunction with amphotericin B to treat cryptococcosis or candidiasis. It is effective also against many dematiaceous fungal infections. It penetrates well into all tissues, including cerebrospinal fluid. Mechanism of action Flucytosine is actively transported into fungal cells by a permease. It is converted by the fungal enzyme cytosine deaminase to 5- fluorouracil and incorporated into 5- fluorodexoyuridylic acid monophosphate, which interferes with the activity of thymidylate synthetase and DNA synthesis. Mammalian cells lack cytosine deaminase and are therefore protected from the toxic effects of fluorouracil. Unfortunately, resistant mutants emerge rapidly, limiting the utility of flucytosine. Indications Flucytosine is used mainly in conjunction with amphotericin B for treatment of cryptococcosis and candidiasis. In vitro, it acts synergistically with amphotericin B against these organisms, and clinical trials suggest a beneficial effect of the combination, particularly in cryptococcal meningitis. The combination has also been shown to delay or limit the emergence of flucytosine-resistant mutants. By itself, flucytosine is effective against chromoblastomycosis and other dematiaceous fungal infections Side effects While flucytosine itself probably has little toxicity for mammalian cells and is relatively well tolerated, its conversion to fluorouracil results in a highly toxic compound that is probably responsible for the major side effects. Prolonged administration of flucytosine results in bone marrow suppression, hair loss, and abnormal liver function. The conversion of flucytosine to fluorouracil by enteric bacteria may cause colitis. Azols The antifungal imidazoles (eg, ketoconazole) and the triazoles (fluconazole, voriconazole, and itraconazole) are oral drugs used to treat a wide range of systemic and localized fungal infections. The indications for their use are still being evaluated, but they have already supplanted amphotericin B in many less severe mycoses because they can be administered orally and are less toxic. Mechanism of action The azoles interfere with the synthesis of ergosterol. The various azoles are designed to improve their efficacy, availability, and pharmacokinetics and reduce their side effects. These are fungistatic drugs.  Indications The indications for the use of antifungal azoles will broaden as the results of long-term studies—as well as new azoles—become available. Ketoconazole is useful in the treatment of chronic mucocutaneous candidiasis, dermatophytosis, and nonmeningeal blastomycosis, coccidioidomycosis, paracoccidioidomycosis, and histoplasmosis. Of the various azoles, fluconazole offers the best penetration of the central nervous system. It is used as maintenance therapy for cryptococcal and coccidioidal meningitis. Itraconazole is now the agent of first choice for histoplasmosis and blastomycosis as well as for certain cases of coccidioidomycosis, paracoccidioidomycosis, and aspergillosis. It has also been shown to be effective in the treatment of chromomycosis and onychomycosis due to dermatomycosis. Side effects Ketoconazole is the most toxic, and therapeutic doses may inhibit the synthesis of testosterone and cortisol, which may cause a variety of reversible effects such as gynecomastia, decreased libido, impotence, menstrual irregularity, and occasionally adrenal insufficiency. Fluconazole and itraconazole at recommended therapeutic doses do not cause significant impairment of mammalian steroidogenesis. All the antifungal azoles can cause both asymptomatic elevations in liver function tests and rare cases of hepatitis. Voriconazole causes reversible visual impairment in about 30% of patients. Topical antifungal agents Nystatin is a polyene antibiotic, structurally related to amphotericin B and having a similar mode of action. It can be used to treat local candidal infections of the mouth and vagina. Nystatin may also suppress subclinical esophageal candidiasis and gastrointestinal overgrowth of candida. No systemic absorption occurs, and there are no side effects. However, nystatin is too toxic for parenteral administration.  Topical antifungal agents (2) A variety of antifungal azoles too toxic for systemic use are available for topical administration. Clotrimazole and miconazole are available in several formulations. Econazole, butaconazole, tioconazole, and terconazole are also available. Topical azoles have a broad spectrum of activity. Tinea pedis, tinea corporis, tinea cruris, tinea versicolor, and cutaneous candidiasis respond well to local application of creams or powders. Vulvovaginal candidiasis can be treated with vaginal suppositories or creams. Clotrimazole is also available as an oral troche for treatment of oral and esophageal thrush in immunocompetent patients. Opportunistic mycosis Jawetz et al., Chapter 45 – Medical Mycology