some fungal pathogens

8/9/2019 Some Fungal Pathogens

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Histoplasmosis

y Histoplasma is a genus of dimorphic fungi commonly found in bird and bat fecal material.

y Histoplasma contains a few species, includingH.capsulatumthe causative agent of histoplasmosis

y Histoplasmosis (also known as "Cave disease,"



y The fungus is thermally dimorphic: in theenvironment it grows as a brownish mycelium, and at

body temperature (37 °C in humans) it morphs into a yeast.

y The inoculum is represented principally by microconidia that, once inhaled into the alveolar

spaces, germinate and then transform into budding yeast cells.

y Histoplasmosis is not contagious, but is contracted by inhalation of the spores from disturbed soil.



y Histoplasma capsulatum is found throughout the world.

y It is endemic in certain areas of the United States, incaves in southern and East Africa.

y Positive histoplasmin skin tests occur in as many as90% of the people living in areas where H. capsulatum

is common.



y Symptoms of this infection vary greatly, but the diseaseprimarily affects the lungs.

y Occasionally, other organs are affected; this is calleddisseminated histoplasmosis, and it can be fatal if untreated.

y Histoplasmosis is common among AIDS patients

because of their lowered immune system.



y Most affected individuals have clinically silentmanifestations and show no apparent ill effects.

y The acute phase of histoplasmosis is characterized by non-specific respiratory symptoms, often cough or flu-like.

y Chest X-ray findings are normal in 4070% of cases.

Chronic histoplasmosis cases can resembletuberculosis.

y disseminated histoplasmosis affects multiple organsystems and is fatal unless treated.



Diagnosisy Histoplasmosis can be diagnosed by samples

containing the fungus taken from sputum, blood, or

infected organs.y It can also be diagnosed by detection of antigens in

blood or urine samples by ELISA or PCR .

y It can also be diagnosed by a test for antibodies

against Histoplasma in the blood.



y Histoplasma skin tests indicate whether a person hasbeen exposed, but do not indicate whether they have

the disease.y Formal histoplasmosis diagnoses are often

confirmed only by culturing the f ungus directly.



Coccidioidomycosis

y (also known as "California disease, "Desertrheumatism,"[ is a fungal disease caused by C

occidioides immitis orC

. posadasii.y It is endemic in certain parts of USA and northwesternMexico.



y C . immitis resides in the soil.

y It is dormant during long dry spells, then develops as

a mold with long filaments that break off into airbornespores when the rains come.

y The spores, known as arthroconidia, are swept intothe air by disruption of the soil, such as during

construction or farming.y Infection is caused by inhalation of the particles.



y The disease is not transmitted from person to person.

y C . immitis is a dimorphic saprophytic organism that

grows as a mycelium in the soil and produces aspherule form in the host organism.



y The disease is usually mild, with flu-like symptomsand rashes.

yOn occasion, those particularly susceptible may develop a serious or even fatal illness.

y Serious complications include severe pneumonia, lungnodules, and disseminated disease, where the fungus

spreads throughout the body.



Diagnosisy The fungal infection can be demonstrated by

microscopic detection of diagnostic cells in body

fluids, exudates, sputum and biopsy -tissue.y It can also be detected in culture by morphological

identification.

y With specific nucleotide primers C .immitis DNA can

be amplified by PCR .y An indirect demonstration of fungal infection can be

achieved also by serologic analysis detecting fungalantigen or host antibody produced against the fungus.



Paracoccidioides sp.

y P aracoccidioides is a thermally dimorphic fungus. Although it has been isolated from soil and digestive

tract of some animals.y The genus P aracoccidioides contains one species,P aracoccidioides brasiliensis.



y P aracoccidioides brasiliensis is the causative agent of atrue systemic (endemic) mycosis called

paracoccidioidomycosis.y The spectrum of the disease is wide, varying from an

asymptomatic infection verified by the skin test to asubclinical, symptomatic or chronic infection.

y

The infection may become apparent several years afterexposure.



y The infection is presumably acquired via inhalation of the conidia, followed by primary infection of the lungs.

The degree of pathogenicity may vary and appearsstrain-dependent.

y In addition to the primary pulmonary form of thedisease, acute pulmonary, chronic pulmonary, and

disseminated forms may also be observed.



y In cases of disseminated paracoccidioidomycosis,reticuloendothelial system, skin and mucous

membranes are frequently involved. Lymph nodes may also be infected during the course of the infection. Aortitis may develop.

y Acute pulmonary and disseminated

paracoccidioidomycosis may rarely develop inimmunocompromised host



Macroscopic Features

y For definitive identification of the fungus, mould-to- yeast conversion should be demonstrated.

y Although most strains are sterile and do not sporulate,it is in general accepted that isolates of

P aracoccidioides brasiliensis must be handled withcaution in a biological safety cabinet.



Mucory Mucor is a genus of about 3000 species of moulds

commonly found in soil, digestive systems, plant

surfaces, and rotten vegetable matter.y Colonies of this fungal genus are typically white to

beige or gray and fast-growing.

y Colonies on culture medium may grow to several

centimeters in height. Older colonies become grey tobrown in colour due to the development of spores.



y Most species of M ucor are unable to infect humansand endothermic animals due to their inability to grow

in warm environments close to 37 degrees Celsius.y Thermotolerant species such as M ucor indicus

sometimes cause opportunistic, and often rapidly spreading, necrotizing infections known as

zygomycosis.y Heavy exposure to the spores of Mucor can cause

extrinsic allergic alveolitis, a type 3 (IgG) allergicresponse.



T richosporon spp.

y T richosporon is a yeast isolated from soil, watersamples, vegetables, mammals, and birds. As well as

being a member of the normal flora of mouth, skinand nails, it is the causative agent of superficial anddeep infections in humans.

y T richosporon beigelii is the most significant pathogenin the genus T richosporon.



y T richosporon spp. are the causative agents of whitepiedra, superficial infections and invasive

trichosporonosis.y This fungus has emerged as an opportunistic fungal

pathogen.

y Immunocompromised hosts are particularly under

risk to develop invasive infection.

some fungal pathogens

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