in air, dust, fomites and even among the normal flora that humans are constantly exposed to them
Due to the relative resistance of humans and the comparatively nonpathogenic nature of fungi, most exposures do not lead to
infection
There are an estimated ? species of fungi, but only about ? have been linked to disease in animals.
100,000300
Fungi are, however, the most common and destructive of all pathogens in
plants
Human fungal diseases is called
mycoses
Human fungal diseases (called mycoses) are associated with
true fungal pathogens that exhibit some degree of virulence, or with opportunistic pathogens that take advantage of decreased, or defective, host resistance.
A true fungal pathogen is a species that can
invade and grow in a healthy, nonimmuno-compromised animal host
This action (mycosis due to true fungal pathology) is contrary to the metabolism and adaptation of most fungi which are inhibited by
the relatively high temperature and low oxygen tension environments of most animals
A small number of fungal species have developed the
morphological and physiological adaptations required to survive in these conditions (body heat and low oxygen)
One of the most prominent adaptations is the ability to switch from
hyphal cells typical of the mycelial or mold phase to yeast cells typical of the parasitic phase
One of the most prominent adaptations is the ability to switch from hyphal cells typical of the mycelial or mold phase to yeast cells typical of the parasitic phase. This biphasic characteristic is called
thermal dimorphism, because it is initiated by changing temperature. The organisms that exhibit this ability are called dimorphic fungi.
The species that have developed the morphological and physiological adaption, thermal dimorphism, usually grow as molds at ? oC and yeasts at ? oC.
They usually grow as molds at 30 oC and yeasts at 37 oC.
An opportunistic fungal pathogen differs from a
true pathogen
Opportunistic fungal pathogens are
weakly- to nonvirulent, and are dependent on impairment of the host's defense mechanisms in order to invade and cause infection
Opportunistic pathogens may be associated with infections ranging from
superficial and benign colonizations to deep, chronic, systemic infections that can be fatal
Mycoses due to opportunistic pathogens are increasingly serious as a result of
increased immunocompromise associated with conditions such as AIDS
Some fungal pathogens exist in a category between true pathogens and
opportunists
Some fungal pathogens exist in a category between true pathogens and opportunists. These are not inherently invasive but? Examples..
but can grow when inoculated into skin wounds of healthy hosts. Dermatophytes such as the agents that cause ringworm and athletes foot infections are examples of this type intermediate pathogen
Most fungal pathogens do not require a host to
complete their life cycles, and infections involving them are not communicable
Most fungal pathogens do not require a host to complete their life cycles, and infections involving them are not communicable. Exceptions to this general rule include
some dermatophytes and Candida species that naturally inhabit the human body and are transmissible
Most fungal infections are a result of
random exposure to fungal spores in the environment (usually air, dust, or soil).
True fungal pathogens are distributed in a
predictable pattern that coincides with the pathogen's adaptation to the specific climate , soil, or other factors of a relatively limited geographic region.
Treatment of fungal infections is based primarily on
the use of antifungal drugs
Immunization is not usually effective against
fungal infections, although research is proceeding on immunizations against coccidiomycosis and histoplasmosis
Fungal infections can be classified according to
the type and level of infection, and their degree of pathogenicity.
Fungal infections can be classified according to the type and level of infection, and their degree of pathogenicity. These include
systemic infections, subcutaneous infections, cutaneous infections, superficial infections, and opportunistic infections
The systemic infections caused by true fungal pathogens can all be described by
the same general model. They are restricted to certain endemic regions of the world. These infections are usually initiated when the fungal spores are inhaled into the lower respiratory tract where they germinate in the lungs into yeasts or yeast-like cells that initially produce an asymptomatic or mild primary pulmonary infection which may progress to more serious disease.
The most common true pathogen is
Histoplasma capsulatum, the causative agent of histoplasmosis (also called Ohio Valley Fever, Valley Fever, Darling's Disease, or reticuloendotheliosis). Although this disease has probably affected humans since antiquity, it was not described until 1905 by Dr. Samuel Darling
characteristics of H. capsulatum are?
*typically dimorphic*Growth on culture media below 35 oC is characterized by white or brown, hairlike mycelium *growth at 37 oC produces a creamy, white, textured colonyis distributed on all continents except Australia *The highest incidence rates are in the eastern and central regions of the United States (Ohio Valley)
Histoplasmosis presents an array of manifestations ranging from
benign to severe; acute to chronic; and can produce pulmonary, systemic, or cutaneous lesions
The most severe systemic forms of histoplasmosis occur in individuals with
defective immune systems such as AIDS patients. Systemic disease can result in lesions involving the brain, intestine, adrenal glands, heart, liver, spleen, lymph nodes, bone marrow, and skin. Chronic colonization of patients with emphysema and bronchitis causes chronic pulmonary histoplasmosis, which has symptoms similar to tuberculosis.
Diagnosis may involve detection of the organism in
clinical specimens as well as certain serological tests.
Mild cases of histoplasmosis may resolve without treatment, but chronic or disseminated cases require
aggressive systemic treatment. The primary drug used is amphotericin B, although other antifungal agents are available. Surgery to remove masses in the lungs or other organs is sometimes required.
Coccidioides immitis is the etiologic agent of
coccidiomycosis
Coccidioides immitis has probably lived in the soil for millions of years, but human exposure has been relatively recent coinciding with
the encroachment of humans into its habitat
Coccidioides immitis demonstrates the greatest
virulence of all fungal pathogens
The morphology of Coccidioides immitis is distinctive. It is
dimorphic and produces a moist, white to brown colony with abundant, branching, septate hyphae at 25 oC. This mycelial phase produces arthrospores which germinate at 37-40 oC to form the parasitic phase, which is a spherical cell called a spherule. The spherule swells and cleaves internally to form numerous endospores.
Coccidioides immitis occurs
endemically in natural reservoirs and casually in areas where it has been carried by the wind or animals
High incidences of coccidiomycosis are found in
the southwestern United States, but it is also found in Mexico and parts of Central and South America. Concentrated reservoirs are found in the San Joaquin Valley in California and southern Arizona.
Coccidiomycosis is usually caused by
inhalation of the lightweight arthrospores which convert in the lungs to spherules which swell and rupture releasing many spores to continue the infection. This primary pulmonary infection is not inapparent in about 60% of those infected. The other 40% usually exhibit coldlike symptoms including fever, cough, chest pain, headaches, and general malaise
In about 5 of each thousand cases of Coccidiomycosis, the primary infection does not
resolve and progresses. The chronic progressive pulmonary disease is characterized by nodular growths called fungomas, and cavity formations in the lungs that can compromise respiration. Dissemination of spores into major organs occurs in individuals with impaired immunity causing severe and sometimes fatal results.
Diagnosis of Coccidiomycosis is usually straightforward and involves
microscopic detection of the distinctive spherules in sputum, spinal fluid, and tissue biopsies. The organism can be grown on artificial culture media. Other serological tests are available to assist with diagnosis
Treatment for Coccidiomycosis is
The majority of patients do not require treatment. Amphotericin B is the primary drug of choice for those with disseminated disease. Other antifungal drugs may be beneficial. Minimizing exposure to the fungus in its natural habitat has been effective in preventing infection. Oiling roads and planting vegetation helps reduce spore aerosols, and using dust masks when excavating soil prevents workers from inhaling spores
Blastomyces dermatiditis is the etiologic agent of
blastomycosis (also called Gilchrist's disease or Chicago disease).
Blastomyces dermatiditis is a
dimorphic fungus that exhibits a similar pattern to other dimorphic fungi. The mycelial phase is usually a uniform white to tan colony of thin, septate mycelia. Temperature-induced conversion produces yeasts with buds that are nearly as large as the parent cell.
Blastomyces occurs from
southern Canada to southern Louisiana and from Minnesota to Georgia. Infections have also been reported in Central and South America, Africa, and the Middle East. Humans, dogs, cats, and horses are the primary hosts
The primary portal of entry for Blastomyces is
the respiratory tract. Inhalation of relatively few spores is sufficient to cause infection.
A large proportion of primary pulmonary infections due to Blastomyces are symptomatic. Mild disease is accompanied by
cough, chest pain, hoarseness, and fever. More severe and chronic cases can progress in the lungs, skin, and other organs. Lung absesses and tumor-like nodules are often mistaken for cancer. The chronic cutaneous form of blastomycosis is rather common. Disseminated disease into the bone, central nervous system, spleen, liver, and urogenital tract can last for weeks to years and may eventually destroy the host defense mechanisms
The most desirable diagnostic evidence of blastomycosis is
microscopic observation of the yeast forms with broad-based buds in clinical specimens. Culture and demonstration of dimorphism is diagnostic but can require weeks to be completed. Serological tests are available to verify diagnosis.
Disseminated infections due to Blastomycosis were once almost 100% fatal, but modern drugs have
greatly improved the prognosis. The primary drug of choice for disseminated blastomycosis is amphotericin B. Milder cases may respond to other antifungal agents.
Paracoccidioides brasiliensis is the etiologic agent of
paracoccidiomycosis (also called paracoccidioidal granuloma or South American blastomycosis).
paracoccidiomycosis is the least common of the primary mycoses due its
relatively limited geographic distribution
Characteristics of Paracoccidioides brasiliensis are what?
a dimorphic fungus that forms small, nondescript colonies with scanty, undistinctive spores at room temperature, but develops an unusual yeast form at 37 oC. The yeast form consists of a large, round mother cell with small, narrow-necked buds that sprout from the periphery of the mother cell (appears somewhat like the steering wheel of a ship or spokes of a wheel).
Locatiions Paracoccidioides brasiliensis is found is where?
has been isolated from the cool, humid soils of tropical and subtropical regions of South and Central America particularly Brazil, Columbia, Venezuela, Argentina, and Paraguay. The most common victims are agricultural workers and plant harvesters.
paracoccidiomycosis infections occur where in the body?
Most infections occur in the lungs or skin; and most are benign, self-limited events that go completely unnoticed. In a small minority of patients, the pathogen invades the lungs, skin and mucous membranes (especially of the head), and lymphatic organs
paracoccidiomycosis is diagnoses by?
Diagnosis is made by detection of the distinctive yeast forms in fresh or stained clinical specimens. Culture with demonstration of dimorphism is used for confirmation of diagnosis. Serological tests are also available
The primary drugs used for treatment of paracoccidiomycosis disseminated disease, in order of choice, are
ketoconazole, amphotericin B, and sulfonamide drugs
Certain fungi can cause subcutaneous infections when they are transferred from soil or plants directly into traumatized skin. These infections are called
subcutaneous because they involve tissues within and just below the skin. These fungi are greatly inhibited by higher temperatures of the blood and viscera and rarely disseminate.
Mycoses in this subcataneous infection category include
sporotrichosis, chromo-blastomycosis, phaeohyphomycosis, and mycetoma.
Sporotrichosis is caused by a
very common fungus called Sporothrix schenkii
Overt disease is not common from Sporotrichosis unless an individual has
inadequate immune defenses or is exposed to a large inoculum or a particularly virulent strain. The fungus grows at the site of penetration and develops a small nodule within a few days to months. The nodule subsequently enlarges, becomes necrotic, breaks through the skin, and drains
Chromoblastomycosis and phaeohyphomycosis are
similar infections
Chromo-blastomycosis is caused by a collection of
soil fungi with dark-pigmented mycelia and spores.
The agents of phaeohyphomycosis are a different group of fungi than for chromoblastomycosis. The fungi associated with these diseases are of
low inherent virulence and none exhibit thermal dimorphism.A) Chromoblastomycosis primarily affects men with rural occupations who go barefoot. After a long incubation period (2-3 years), wart-like lesions appear. The lesions are not painful, and patients seldom seek treatment. Secondary bacterial infections may be caused by scratching the nodules. Chromoblastomycosis is often confused with other disease including cancer, syphilis, and blastomycosis
The diseases collectively called phaeohyphomycoses produce unusual and deforming symptoms. The fungi grow slowly from the portal of entry through the
dermis and create large, cutaneous cysts. Victims are usually highly immunocompromised. In patients with underlying diseases such as endocarditis, diabetes, and leukemia; the fungi may spread into the brain, bones, and lungs.
Mycetoma (also called madura foot) is a mycosis usually of the
foot or hand that superficially looks like a tumor. The infection begins when bare skin is pierced by a thorn or sharp plant debris.
The symptoms of mycetoma are
localized abscess in the subcutaneous tissues that gradually swells and drains. Untreated cases that spread to the muscles and bones causing pain and loss of function in the affected body part. Mycetoma has a lengthy course, and is difficult to treat.
Fungal infections that are strictly confined to the nonliving epidermal tissues (stratum corneum) and its derivatives (hair and nails) are called
cutaneous mycoses, or dermatophytoses. Common terms used in reference to these diseases are ringworm and tinea
cutaneous mycoses fungal infections , or dermatophytoses, have members of the genera (name 3) that are involved in these infections
Trichophyton, Microsporum, and Epidermophyton
The etiologic agent of a particular type of ringworm varies from
person to person, location to location, and is not restricted to a specific genus or species.
The dermatophytes are closely related and morphologically similar and they can be
difficult to differentiate.
Most dermatophyte infections involve
a long incubation period (months), followed by localized inflammation and allergic reactions to the fungal proteins
Dermatophytoses can be organized according to
the area of the body they affect, their mode of acquisition, and their pathologic appearance
Tinea Capitis -
ringworm of the scalp
Tinea Barbae -
ringworm of the beard ("barber's itch")
Tinea Corporis -
ringworm of the body
Tinea Cruris -
ringworm of the groin ("jock itch")
Tinea Pedis -
ringworm of the foot ("athlete's foot", "jungle rot")
Tinea Manuum -
ringworm of the hand
Tinea Unguium -
ringworm of the fingernails or toenails
Superficial mycoses involve the ? and are usually nuisance infections with ? rather than inflammatory effects
outer epidermal surface cosmetic
Tinea versicolor is caused by the
yeast Malassezia furfur
the characteristics of yeast Malassezia furfur are
This organism is a normal inhabitant of human skin that feeds on the high oil content of skin glands. In some individuals, it causes a mild, chronic scaling and interferes with the production of pigments by melanocytes. Skin of the trunk, face, and limbs takes on a discolored, mottled appearance.
White Piedra is caused by
Trichosporon beigelii.
White Piedra is characterized by
a white to yellow mass that develops on the shaft of scalp, pubic, or axillary hair. Sometimes the mass is invaded by brightly colored bacterial contaminants, with amazing resultsNOTcommon in the United States
Black Piedra is caused by ?It is characterized by?
Piedraia hortae.dark brown to black gritty nodules mainly on scalp hairs. NOTcommon in the United States
Opportunistic fungal infections depend on certain predisposing factors, particularly those that
reduce host resistance
Prominent opportunistic pathogens include .
Candida, Cryptococcus, Pneumocystis, and some filamentous fungi such as Aspergillus and certain zygomycetes
Candida albicans is an
extremely widespread yeast that causes candidiasis (or moniliasis) which has manifestations ranging from short-lived, superficial skin infections to overwhelming, fatal systemic diseases.
Thrush is a
white, patchy infection involving the membranes of the oral cavity or throat, usually seen in infants or elderly debilitated patients
Vulvovaginal candidiasis (commonly called "yeast infection") is characterized by
a yellow to white discharge, inflammation, painful ulcerations, and itching. Individuals most at risk include those taking oral antibiotics, and those who are diabetic or pregnant; all conditions that alter the normal vaginal flora. Candidal vaginitis can also pose a risk to neonates who may be infected during childbirth. Vaginal candidiasis may be spread to male partners during sexual intercourse
Candida albicans may cause
onychiomycosis, which is a fungal infection of keratinized structures such as nails and skin. Individuals whose hands or feet are constantly immersed in water are particularly at risk for this type infection
Cutanaeous candidiasis can complicate
burns and can produce a scalded rash on the skin of neonates
Other candidal infections include
intertriginous infections in moist areas where skin rubs against skin (i.e. beneath the breasts, in the armpits, and in the groin).
Cryptococcus neoformans is associated with
infections involving the respiratory system, central nervous system, and mucocutaneous systems. The organism is a spherical to ovoid yeast with a prominent capsule that is important to its pathogenesis
The primary portal of entry for Cryptococcus neoformans is the
respiratory tract. Most lung infections are subclinical and rapidly resolved.
Major issues concerning Cryptococcus neoformans are
The yeasts may escape into the blood, sometimes intensified by weakened host defenses. Severe complications can result. C. neoformans has an extreme affinity for the brain and meninges. Tumor-like masses may form in these locations causing headache, mental changes, coma, paralysis, vision disturbances, and seizures. In some cases, the infection may disseminate into the skin, bones, and viscera.
Pneumocystis carinii was actually discovered in ?but remained relatively obscure until it achieved clinical prominence as the etiologic agent of ?is the most prominent opportunistic infection in?
1909 pneumocystis (carinii) pneumonia ("PCP") AIDS patients
The taxonomic status of Pneumocystis carinii is uncertain. Its life cycle and epidemiology is not well known. It has characteristics of
both fungi and protozoa
Competent immune defense mechanisms prevent infection by Pneumocystis carinii . In individuals with compromised immune defenses, massive numbers of these organisms adhere to
lung pneumocytes and cause an inflammatory condition. Symptoms are nonspecific and include cough, fever, shallow respiration, and cyanosis
Traditional antifungal drugs are ineffective against Pneumocystis carinii . Improved therapy for AIDS patients has reduced the mortality associated with PCP. The primary treatments for PCP are
pentamidine and cotrimoxazole (sulfamethoxazole / trimethoprim).
Other opportunistic infections may be caused by molds that are members of the genus
Aspergillus and zygomycetes of the genera Rhizopus, Absidia, and Mucor.
Aspergillosis is almost always an
opportunistic infection and usually affects the lungs
Zygomycoses are seen in increasing numbers in
critically ill patients with underlying debilities
what is a formite
any inanimate object
unbranched sporangiophore with rhizoids that appear opposite the point where the stolon arises at the base of the sporangiophore describes which zygomycetes