Lecture (3) mycology, Dr. kareema Amine Alkhafaji, Assistant professor.
The Subcutaneous Mycoses
These are chronic, localized infections of the skin and subcutaneous tissue following the traumatic implantation of the aetiologic agent. The causative fungi are all soil saprophytes of regional epidemiology whose ability to adapt to the tissue environment and elicit disease is extremely variable.
Sporotrichosis
Primarily a chronic mycotic infection of the cutaneous or subcutaneous tissues and adjacent lymphatics characterized by nodular lesions which may suppurate and ulcerate. Infections are caused by the traumatic implantation of the fungus into the skin, or very rarely, by inhalation into the lungs. Secondary spread to articular surfaces, bone and muscle is not infrequent, and the infection may also occasionally involve the central nervous system, lungs or genitourinary tract.
Distribution: World-wide particularly tropical and temperate regions.
Aetiological Agent: Sporothrix schenckii, commonly found in soil and on decaying
vegetation.
Chromoblastomycosis
A mycotic infection of the cutaneous and subcutaneous tissues characterized by the development in tissue of dematiaceous (brown-pigmented), planate-dividing, rounded sclerotic bodies. Infections are caused by the traumatic implantation of fungal elements into the skin and are chronic, slowly progressive and localized. Tissue proliferation usually occurs around the area of inoculation producing crusted, verrucose, wart-like lesions.
Distribution: World-wide but more common in bare footed populations living in
tropical regions .
Aetiological Agents: Various dematiaceous hyphomycetes associated with decaying
vegetation or soil, especially Phialophora verrucosa, Fonsecaea
pedrosoi, F. compacta and Cladosporium carrionii.
Mycetoma
A mycotic infection of humans and animals caused by a number of different fungi and actinomycetes characterized by draining sinuses, granules and tumefaction. The disease results from the traumatic implantation of the aetiologic agent and usually involves the cutaneous and subcutaneous tissue, fascia and bone of the foot or hand. Sinuses discharge serosanguinous fluid containing the granules which vary in size, colour and degree of hardness, depending on the aetiologic species, and are the hallmark of mycetoma.
Distribution: World-wide but most common in bare-footed populations living in
tropical or subtropical regions.
Aetiological Agents: Actinomycotic mycetoma: Nocardia, Actinomadura and
Streptomyces. Eumycotic mycetoma: Madurella, Acremonium, Pseudallescheria,
Exophiala, Leptosphaeria, Curvularia, Fusarium, Aspergillus etc.
INFECTIOUS DISEASE MYCOLOGY
Dimorphic Systemic Mycoses
These are fungal infections of the body caused by dimorphic fungal pathogens which can overcome the physiological and cellular defences of the normal human host by changing their morphological form. They are geographically restricted and the primary site of infection is usually pulmonary, following the inhalation of conidia.
Histoplasmosis
An intracellular mycotic infection of the reticuloendothelial system caused by the inhalation of the fungus. Approximately 95% of cases of histoplasmosis are inapparent, subclinical or benign. Five percent of the cases have chronic progressive lung disease, chronic cutaneous or systemic disease or an acute fulminating fatal systemic disease. All stages of this disease may mimic tuberculosis.
Distribution: World-wide, especially U.S.A. Sporadic cases do occur in Australia.
Aetiological Agent: Histoplasma capsulatum, especially from soil enriched with excreta
from chicken, starlings and bats.
Coccidioidomycosis
Initially, a respiratory infection, resulting from the inhalation of conidia, that typically resolves rapidly leaving the patient with a strong specific immunity to re-infection. However, in some individuals the disease may progress to a chronic pulmonary condition or as a systemic disease involving the meninges, bones, joints and subcutaneous and cutaneous tissues.
Distribution: Endemic in south-western U.S.A., northern Mexico and various centers
in South America.
Aetiological Agent: Coccidioides immitis, a soil inhabiting fungus.
Opportunistic Systemic Mycoses
Opportunistic fungal infections of the body occur almost exclusively in debilitated patients whose normal defence mechanisms are impaired. The organisms involved are cosmopolitan fungi which have a very low inherent virulence. The increased incidence of these infections and the diversity of fungi causing them, has paralleled the emergence of AIDS and the use of antibiotics, cytotoxins, immunosuppressive, steroids and other macro disruptive procedures that result in lowered resistance of the host.
Candidiasis
A primary or secondary mycotic infection caused by members of the genus Candida. The clinical manifestations may be acute, subacute or chronic to episodic. Involvement may be localized to the mouth, throat, skin, scalp, vagina, fingers, nails, bronchi, lungs, or the gastrointestinal tract, or become systemic as in septicaemia, endocarditis and meningitis. In healthy individuals, Candida infections are usually due to impaired epithelial barrier functions and occur in all age groups, but are most common in the newborn and the elderly. They usually remain superficial and respond readily to treatment.
Systemic candidiasis is usually seen in patients with cell-mediated immune deficiency, and those receiving aggressive cancer, immunosuppression, or transplantation therapy.
Several species of Candida may be aetiological agents, most commonly, Candida albicans and rarely C. tropicalis, C. krusei. C. parapsilosis, C. guilliermondii, C. kefyr (C. pseudotropicalis) and C.(Torulopsis) glabrata. All are ubiquitous and occur naturally on humans.
Percentages of Candida sp. isolates from the
Predisposing Factors for the Development of Candidiasis
Impaired Epithelial Barrier
Burns Wounds/abrasions, Hydration/maceration, Occlusion, Indwelling catheters Foreign bodies (dentures, etc),Increased gastric pH, Cytotoxic agents and Irradiation Antibiotics
Constitutional Disorders
Diabetes mellitus Hypoadrenalism
Hypothyroidism Hypoparathyroidism
Polyendocrinopathy Pregnancy/oral contraceptives
Malnutrition Malabsorption
Iron deficiency Zinc deficiency
Biotin deficiency Hypovitaminosis A
Neutrophil and Macrophage Disorders
Malignancy and Haematologic Disorders
Drugs and Therapeutic Agents
Antibiotics Corticosteroids
Colchicine ,Phenylbutazone
Cytotoxic agents Antimetabolites
Irradiation Immunosuppressive agents
Cryptococcosis
A chronic, subacute to acute pulmonary, systemic or meningitic disease, initiated by the inhalation of basidiospores and/or desiccated yeast cells of C. neoformans. Primary pulmonary infections have no diagnostic symptoms and are usually subclinical. On dissemination, the fungus usually shows a predilection for the central nervous system, however skin, bones and other visceral organs may also become involved. Although C. neoformans is regarded as the principle pathogenic species, C. albidus and C. laurentii have on occasion also been implicated in human infection.
Clinical material: Cerebrospinal fluid (csf), sputum, pus, blood and biopsy tissue.
C. neoformans is an encapsulated basidiomycetous yeast-like fungus which has been divided into two varieties; C. neoformans var. neoformans and C. neoformans var. gattii.
C. neoformans var. neoformans (A and D serotypes) has a world-wide distribution and is now one of the most significant world-wide opportunistic pathogens in humans, especially in AIDS patients. It has been isolated from various sources in nature and is noted for its association with accumulations of avian guano, especially with pigeon excreta. The fungus has also been isolated from the dung of caged birds including canaries, parrots and budgerigars. Other environmental isolations of C. neoformans var.neoformans have been from rotting vegetables, fruits and fruit juices, wood, dairy products and soil. C. neoformans var. gattii (serotypes B and C) has a more restricted global distribution corresponding to a subtropical to tropical climate. Environmental isolations have now established that C. neoformans var. gattii has a specific ecological association with Eucalyptus camaldulensis (the river red gum) and
E. tereticornis (the forest red gum).
Zygomycosis (Mucormycosis)
Zygomycosis in the debilitated patient is the most acute and fulminate fungal infection known. The disease typically involves the rhino-facial-cranial area, lungs, gastrointestinal tract, skin, or less commonly other organ systems. It is often associated with acidosis diabetes, malnourished children,severely burned patients and other diseases such as leukemia and lymphoma, immunosuppressive therapy, or use of cytotoxins and corticosteroids. The infecting fungi have a predilection for invading vessels of the arterial system, causing embolization and subsequent necrosis of surrounding tissue. The aetiological agents are cosmopolitan members of the Mucorales, including Rhizopus arrhizus/oryzae,
Rhizopus microsporus, Rhizomucor pusillus, Absidia corymbifera, Cunninghamella bertholletiae,Mucor species, Saksenaea vasiformis, Apophysomyces elegans and Mortierella wolfii.
Clinical material: Skin scrapings from cutaneous lesions; sputum and needle biopsies from pulmonary lesions; nasal discharges, scrapings and aspirates from sinuses in patients with rhinocerebral lesions; and biopsy tissue from patients with disseminated disease.
Aspergillosis
Aspergillosis is a spectrum of diseases of humans and animals caused by members of the genus Aspergillus. These include (1) mycotoxicosis due to ingestion of contaminated foods; (2) allergy and sequelae to the presence of conidia or transient growth of the organism in body orifices; (3) colonization without extension in preformed cavities and debilitated tissues; (4) invasive, inflammatory,granulomatous, necrotizing disease of lungs, and other organs; and rarely (5) systemic and fatal disseminated disease. The type of disease and severity depends upon the physiologic state of the host and the species of Aspergillus involved. The aetiological agents are cosmopolitan and include; Aspergillus fumigatus, A. flavus, A. niger, A. nidulans and A. terreus.
Clinical material: Skin and nail scrapings; urine, sputum and bronchial washings; cerebrospinal fluid,pleural fluid and blood; tissue biopsies from various visceral organs and indwelling catheter tips.
Hyalohyphomycosis
A mycotic infection of man or animals caused by a number of hyaline (non-demtiaceous) hyphomycetes where the tissue morphology of the causative organism is mycelial. This separates it from phaeohyphomycosis where the causative agents are brown-pigmented fungi. Hyalohyphomycosis is general term used to group together infections caused by unusual hyaline fungal pathogens that are not agents of otherwise-named infections. Aetiological agents include species of Penicillium,Paecilomyces, Acremonium, Beauveria, Fusarium, Trichoderma and Scopulariopsis.
Clinical material: Skin and nail scrapings; urine, sputum and bronchial washings; cerebrospinal fluid,
pleural fluid and blood; tissue biopsies from various visceral organs and indwelling catheter tips.