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BloodbornePathogens

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Classification of Fungi

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Introduction to FungiFungi is a general term used to encompass the diverse morphologic forms of yeasts and molds. Originally classified as primitive plants without chlorophyll,the fungi are placed in the kingdom Fungi.

Fungi share with bacteria the important ability to break down complex organic substances of almost every type (cellulose) and are essential to the recycling of carbon and other elements in the cycle of life. Fungi are important as foods and to the fermentation process in the development of substances of industrial and medical importance, including alcohol, antibiotics, other drugs, and foods.

Relatively few types of fungus are pathogenic for humans, whereas most plant diseases are caused by fungi.

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Aspergillus niger

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Introduction

Bloodborne Pathogens

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Cause of DiseaseSome fungi can cause serious diseases in humans, several of which may be fatal if untreated. These include aspergillosis, candidiasis, coccidioidomycosis, cryptococcosis, histoplasmosis, mycetomas, and paracoccidioidomycosis. Furthermore, persons with immunodeficiencies are particularly susceptible to disease by genera such as Aspergillus, Candida, Cryptoccocus, Histoplasma, and Pneumocystis. Other fungi can attack eyes, nails, hair, and especially skin, the so-called dermatophytic and keratinophilic fungi, and cause local infections such as ringworm and athlete’s foot. Fungal spores are also a cause of allergies, and fungi from different taxonomic groups can evoke allergic reactions.

Microscopic image (100-fold magnification) of Aspergillus nigar, grown on Sabouraud agar medium.

Histoplasma capsulatum (or Ajellomyces capsulatum)

causes Histoplasmosis which mainly affects lungs.

A mycosis is a fungal infection. Mycoses are common, and a variety of environmental and physiological conditions can contribute to the development of fungal diseases. Inhalation of fungal spores or localized colonization of the skin may initiate persistent infections; therefore, mycoses often start in the lungs or on the skin.

At Risk

People are at risk of fungal infections when they are taking strong antibiotics for a long period of time because antibiotics kill not only damaging bacteria, but healthy bacteria as well. This alters the balance of microorganisms in the mouth, vagina, intestines and other places in the body, and results in an overgrowth of fungus.

Individuals with weakened immune systems are also at risk of developing fungal infections. This is the case of people with HIV/AIDS, people under steroid treatments, and people taking chemotherapy. People with diabetes also tend to develop fungal infections. Very young and very old people, also, are groups at risk.

Cause of Disease

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Classification of FungiMycoses are classified according to the tissue levels initially colonized.

Superficial mycoses

Superficial mycoses are limited to the outermost layers of the skin and hair. An example of such a fungal infection is Tinea versicolor, a fungus infection that commonly affects the skin of young people, especially the chest, back, and upper arms and legs. Tinea versicolor is caused by a fungus that lives in the skin of some adults. It does not usually affect the face. This fungus produces spots that are either lighter than the skin or a reddish-brown. This fungus exists in two forms, one of them causing visible spots. Factors that can cause the fungus to become more visible include high humidity, as well as immune or hormone abnormalities. However, almost all people with this very common condition are healthy.

Cutaneous mycoses

Cutaneous mycoses extend deeper into the epidermis, and also include invasive hair and nail diseases. These diseases are restricted to the keratinized layers of the skin, hair, and nails. Unlike the superficial mycoses, host immune responses may be evoked, resulting in pathologic changes expressed in the deeper layers of the skin. The organisms that cause these diseases are called dermatophytes. The resulting diseases are often called ringworm (even though there is no worm involved) or tinea. Cutaneous mycoses are caused by Microsporum, Trichophyton, and Epidermophyton fungi, which together comprise 41 species.

Ringworm appears as red patches which are often redder around the outside with normal skin tone in the center.

One common disease is the athlete’s foot which most commonly affects men and children before puberty. It is divided in three categories: chronic interdigital athlete’s foot, chronic scaly athlete’s foot, and acute vesicular athlete’s foot.

Classification of Fungi

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Classification of Fungi (continued)Subcutaneous mycoses

Subcutaneous mycoses involve the dermis, subcutaneous tissues, muscle, and fascia. These infections are chronic and can be initiated by piercing trauma to the skin, which allows the fungi to enter. These infections are difficult to treat and may require surgical interventions such as debridement.

Systemic mycoses due to primary pathogens

Systemic mycoses due to primary pathogens originate primarily in the lungs and may spread to many organ systems. Organisms that cause systemic mycoses are inherently virulent. Generally, primary pathogens that cause systemic mycoses are dimorphic.

Systemic mycoses due to opportunistic pathogens

Systemic mycoses due to opportunistic pathogens are infections of patients with immune deficiencies who would otherwise not be infected. An example of an opportunistic pathogen is a form of fungal meningitis called cryptococcal meningitis. Patients treated for cancer or chronic illnesses where treatments and/or the disease itself compromise the patient’s immune system are particularly vulnerable. Most common in AIDS patients, cryptococcal fungal meningitis cases have increased globally during the past decade. National health data estimates the incidence to be approximately 1,500 cases annually in the U.S. Other examples of opportunistic mycoses include Candidiasis, Cryptococcosis and Aspergillosis.

In October 2012, an outbreak of fungal meningitis was reported in the United States. The U.S. Centers for Disease Control and Prevention (CDC) traced the outbreak to contaminated medication used for epidural steroid injections. The U.S. Food and Drug Administration (FDA) examined foreign materials from unopened vials under microscope and found fungal matter. The fungus was found in the cerebrospinal fluid of several patients, which confirmed that the fungus caused the meningitis. A black mold called Exserohilum rostratum was found in the majority of the cases identified.

Treatment• Antifungal drugs are used to treat mycoses. • Depending on the nature of the infection, a topical or systemic agent may be used. • Yeast infections in the vagina, caused by candida albicans, can be treated with

medicated suppositories such as tioconazole and pessaries whereas skin yeast infections are treated with medicated ointments.

Prevention• Keeping the skin clean and dry, as well as maintaining good hygiene is important. • Because fungal infections are contagious, it is important to consider isolation

procedures and extremely important to use gloves and clean hands after patient care.

Classification of Fungi(continued)

Exserohilum rostratum

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GlossaryAthlete’s foot (noun) \ ath-leet z\ foot\Also known as ringworm of the foot or tinea pedis, is a fungal infection of the skin that causes scaling, flaking, and itching of affected areas

Debridement (noun) \ dih-breed-muhnt\The medical removal of dead, damaged or infected tissue to improve the healing potential of the remaining healthy tissue

Dimorphism (noun) \ dahy-mawr-fiz-uhm\Switching between two cell-types

Epidermis (noun) \ ep-i-dur-mis\Composed of the outermost layers of cells in the skin; ‘epi’ in Greek means ‘over’ or ‘upon’, which together with ‘dermis’ forms the cutis

Fungal meningitis (noun) \ fuhng-guh l\ men-in-jahy-tis\Refers to meningitis caused by a fungal infection

Meningitis (noun) \ men-in-jahy-tis\An inflamation of the protective membranes covering the brain and spinal cord, known collectively as the meninges

Steroid (noun) \ ster-oid\Any of a large number of hormonal substances with a similar basic chemical structure, produced mainly in the adrenal cortex and gonads. Steroids are chemically related to sterols

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Bloodborne Pathogens

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Review• Fungi is a general term used to encompass the diverse morphologic forms of

yeasts and molds.

• Some fungi can cause serious diseases in humans, several of which may be fatal if untreated. Furthermore, persons with immunodeficiencies are particularly susceptible to fungal disease.

• Other fungi can attack eyes, nails, hair, and especially skin, and cause local infections such as ringworm and athlete’s foot.

• Fungal spores are also a cause of allergies, and can evoke allergic reactions. • People are at risk of fungal infections when they are taking strong antibiotics

for a long period of time because antibiotics kill not only damaging bacteria, but healthy bacteria as well. This alters the balance of microorganisms in the mouth, vagina, intestines and other places in the body, and results in an overgrowth of fungus.

• Antifungal drugs are used to treat fungi. Depending on the nature of the infection, a topical ointment, suppository or systemic agent may be used.Review

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