Published on March 9, 2014
Opportunistic mycoses Dr. Pendru Raghunath Reddy
Opportunistic mycoses Occurrs in human’s with a compromised immune system Causative agents are normal resident flora that become pathogenic only when the host's immune defenses are altered, as in immunosuppressive therapy, in a chronic disease, such as diabetes mellitus, or during steroid or antibacterial therapy that upsets the balance of bacterial flora in the body
Causative agents • Candida species • Cryptococcus neoformans • Aspergillus species • Zygomycosis (Rhizopus, mucor, absidia) • Penicillium species • Fusarium species • Alternaria species ***ANY fungus found in nature may give rise to opportunistic mycoses ***
Aspergillosis • Aspergillus species are ubiquitous saprophytes in nature • In nature >300 species of Aspergillus exist, few are important as human pathogens • • • • • 1 A.fumigatus 2 A.niger 3 A.flavus 4 A.terreus 5 A.nidulans
Pathogenesis 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, the conidia may germinate to produce hyphae that invade the lungs and other tissues
Fungal spores enters through respiratory tract
The Aspergillus species can cause a variety of clinical syndromes 1. Pulmonary aspergillosis a) Allergic asthma b) Bronchopulmonary aspergillosis c) Aspergilloma 2. Invasive aspergillosis 3. Superficial infections
Allergic asthma In some atopic individuals, development of IgE antibodies to the surface antigens of Aspergillus conidia elicits an immediate asthmatic reaction upon subsequent exposure Bronchopulmonary aspergillosis The conidia germinate and hyphae colonize the bronchial tree without invading the lung parenchyma The condition is made worse by the development of hypersensitivity to the fungus
Aspergilloma • Fungus colonize preexisting (Tuberculosis ) cavities in the lung and form compact ball of mycelium which is later surrounded by dense fibrous wall presents with cough, sputum production • Haemoptysis occurs due to invasion of blood vessels • Cases of aspergilloma rarely become invasive
Invasive aspergillosis In invasive aspergillosis, the fungus first causes pneumonia, actively invades the lung tissue and disseminates to involve other organs, for example, the brain, kidneys or heart This form occurs in severly immuno compromised individuals who have a serious underlying illness Neutropenia is the most common predisposing factor and A. fumigatus is the species most frequently involved
Superficial infections 1. Sinusitis 2. Mycotic keratitis 3. Otomycosis
Laboratory diagnosis Specimens Sputum, other respiratory specimens, lung biopsy specimens Microscopic examination KOH mount The fungus appears as non-pigmented septate mycelium, 3-5 µm in diameter with chatracteristic dichotomous branching and an irregular outline Rarely the characteristic sporing heads of Aspergillus species are present
Culture Aspergillus species grow readily on SDA without cycloheximide at 25-370C Colonies appear after 1-2 days of incubation Species are identified according to the morphology of their conidial structures Skin tests Skin tests with Aspergillus species antigen are useful for the diagnosis of allergic broncho pulmonary aspergillosis
Treatment Invasive aspergillosis is treated with intravenous amphotericin B In recent years, intravenous formulations of azoles, such as voriconazole, are being evaluated
Zygomycosis Also called as Mucormycosis, Phycomycosis It is an invasive disease caused by zygomycetes, principally by the species of Rhizopus, Mucor, Rhizomucor, Absidia These fungi are ubiquitous theromtolerant saprophyte; spores are present in air and dust The conditions that place patients at risk include acidosis, leukemias, lymphoma, corticosteroid treatment, severe burns, immunodeficiencies
Clinical manifestations There are a number of different clinical varieties of mucormycosis 1. Rhinocerebral Mucormycosis 2. Thoracic Mucormycosis 3. Other sites of invasion
Rhinocerebral Mucormycosis 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 It is almost invariably associated with acute diabetes mellitus or with debilitating diseases such as leukemia or lymphoma
Thoracic Mucormycosis This follows inhalation of the sporangiospores with invasion of the lung parenchyma and vasculature In both locations, ischemic necrosis causes massive tissue destruction Other sites of invasion Primary cutaneous infections such as skin infections following burns or surgery have also been reported Subcutaneous zygomycosis cases are also reported
Laboratory diagnosis Secimens Nasal discharge, sputum and biopsy specimens Microscopy KOH mount, may reveal the characteristic broad, aseptate, branched mycelium and sometimes distorted hyphae They are seen much more clearly when stained with methenamine-silver stain The hyphae of these fungi do not stain with PAS
Broad, aspetate hyphae in tissue sections
Culture The fungi are readily isolated on SDA with antibiotics without cycloheximide, producing abundant cottony colonies Identification of the species is based on the sporangial structures
Treatment Intravenous amphotericin B combined, where appropriate with surgical drainage
Penicillosis There are more than 150 species; most important species Penicillium marneffei Penicillium marneffei –thermally dimorphic fungi Penicillium species are saprophytes; present in the environment and grow on various substrates such as bread, jam, fruit and cheese
Pathogenesis and clinical features P. marneffei has been reported to be an important opportunistic pathogen in the HIV infected It causes disseminated infection with multiple organ involvement
Laboratory diagnosis The yeast are small, oval, 2-4 µm in diameter The mycelia form produces red diffusible pigment and morphologically resembles other members of the Penicillium species Penicillum species possess septate hyphae with branched conidiophores, with two rows of sterigmata bearing chains of rows; the appearance is like a brush or broom
Dimorphic chaterization of Pencillium marneffei
Mycelial growth of P. marneffei Microscopic examination
Treatment Penicillosis can be treated with amphotericin B and followed by oral itraconazole
With opportunistic infections, the equation is tilted in favor of "disease" because resistance is lowered when the host is immunocompromised.
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