medical mycology for nurses in kenya
TRANSCRIPT
Medical
MycologyIntroduction
to
Basics
for nurses
WALTER WASWA,
BSC.MLS
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Reference books
• Brooks, Geo. F. etal, (2007):Medical microbiology, 24ed. The McGraw-Hill Companies, Inc. New York.-----an e book in the library.
• Other books on microbiology in the library.
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Introduction• Mycology is the study of fungi
• The study of fungi is known as mycology and scientist who study fungi is known is a mycologist.
• Fungal infections are termed as mycoses
• Fungi are differ from bacteria and other prokaryotes.
1. Cell walls containing chitin (rigidity & support), mannan & other polysaccharides
2. Cytoplasmic membrane contains ergosterols
3. Possess true nuclei with nuclear membrane & paired chromosomes.
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Characteristics of Fungus
• Diverse group of chemo heterotrophs– > 90,000 known species
• Saprophytes– Digest dead organic matter
• Parasites– Obtain nutrients from tissues of organisms
• Molds & mushrooms are multicellular
• Yeasts are unicellular
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CHARACTERISTICS OF FUNGI (Continued)
Dimorphic Fungi
Can exist as both multicellular fungi (molds) and yeasts.
Many pathogenic species.
– Mold form produces aerial and vegetative hyphae.
– Yeast form reproduces by budding.
Dimorphism in pathogenic fungi typically depends on
temperature:
– At 37oC: Yeast form.
– At 25oC: Mold form.
Dimorphism in nonpathogenic fungi may depend on other
factors: Carbon dioxide concentration.
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Understanding the Structure of Fungi
• Yeasts and molds have different structural and reproductive characteristics– Yeast are unicellular, nucleated rounded fungi while
molds are multicellular, filamentous fungi
– Yeast reproduce by a process called budding while molds produce spores to reproduce
– Some yeast are opportunistic pathogens in that they cause disease in immuno-compromised individuals
– Yeast are used in the preparation in the variety of foods
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Predisposing factors to fungal infection
1.Use of Antibiotics,
2.Use of steroids,
3.Immunosuppressive
conditions
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Fungal Diseases• Mycosis- fungal infection
–< 100 cause human disease–Not highly contagious–Humans acquire from nature
• Groups based on degree on tissue involvement and mode of entry
• Cutaneous mycoses-dermatophytes– Epidermis, hair & nails–Contagious-direct or indirect contact– Secrete keratinase that degrades keratin
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CLASSIFICATION
• Depending on cell morphology
1. Yeasts
2. Yeast like fungi
3. Molds
4. Dimorphic fungi
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1.Yeasts• Unicellular fungi
which reproduce by budding
• On culture -produce smooth, creamy colonies
e. g Cryptococcus neoformans (capsulated yeast)
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2.Yeast like fungi
• Grow partly as yeasts and partly as elongated cells resembling hyphae which are called pseudo hyphae. e.g. Candida albicans
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3.Molds/ Filamentous
fungi• Form true mycelia &
reproduce by formation of different types of spores.
• Vegetative/ aerial hyphae
e.g. Rhizopus, Mucor
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4. Dimorphic fungi• Occur in 2 forms
Molds (Filaments) – 25C (soil)Yeasts – 37C (in host tissue)
Most fungi causing systemic infections are dimorphic: – Histoplasma capsulatum– Blastomyces dermatidis– Paracoccidioides brasiliensis– Coccidioides immitis– Penicillium marneffei– Sporothrix schenkii
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Reproduction in fungi • Sexual - formation of Zygospore, ascospores
or basidiospores
• Asexual reproduction – budding or
fission
• Asexual spores are formed on or in specialized structures.
• Vary in size, shape & colour but these characteristics are constant for a particular species.
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conidia-asexual reproductive
structure –can be inhaled• Micro conidia
- Small, single celled
• Macro conidia – Large, single or many celled
• Seeds
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Structure• The main body of most fungi is made up of fine,
branching, usually colourless threads called hyphae
• Several of these these hyphae, all intertwining to make up a tangled web called the mycelium
• Most fungi are multinucleate and multicellular organisms with cross wall called septa or aseptate(coenocytic)
• Yeasts are unicellular
• One major difference is that most fungi have cell walls that contain chitin, unlike the cell walls of plants, which contain cellulose
Single Hyphae
Reproduction
• Life cycle involves the fusion of hyphae from two individuals (Male & Feamle
• Each parent hyphae has haploid nuclei• The fusion of hyphae is called plasmogamy.• The fused hyphae containing haploid nuclei from
two individuals is heterokaryotic.• In some cases, plasmogamy results in cells with
one nucleus from each individual. This condition is called dikaryotic.
• Two nuclei that originated from different individuals fuse to form a diploid zygote.
• Meiosis then produces either four haploid nuclei or four haploid cells.
YEASTS AND MOLDS
•Molds - multicellular
•Yeasts - unicellular
•The simplest form of growth is budding.
•Buds are called blastoconidia.
•Seen in yeasts.
..Reproduction in yeast
• Reproduce by budding.
Microbiology: A Clinical Approach © Garland Science
YEASTS
© CDC/ Dr. Edwin P. Ewing, Jr.
.
The life cycle of Rhizopus stolonifera ( bread
mold).
Fungal Infections/ Mycoses
• superficial
• CUTANEOUS MYCOSES
• SUBCUTANEOUS MYCOSES
• SYSTEMIC
• OPPORTUNISTIC
• FUNGAL TOXINS AND ALLERGIES
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SUPERFICIAL MYCOSES
Fungal infections that do not involve a tissue
response:
…SUPERFICIAL MYCOSES
•Pityriasis Versicolor. chronic mild superficial
infection of the stratum corneum caused by
Malassezia globosa,
•M restricta,
•M furfur complex.
• Invasion of the cornified skin and the host
responses are both minimal.
SUPERFICIAL MYCOSES
• Tinea Nigra- is a superficial chronic and asymptomatic infection of the stratum corneum caused by the dematiaceous fungus Hortaea (Exophiala) werneckii
• This condition is more prevalent in warm coastal regions and among young women.
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SUPERFICIAL MYCOSES
• Piedra
• Black piedra is a nodular infection of the hair shaft caused by Piedraia hortai.
• White piedra, due to infection with Trichosporon species, presents as larger, softer, yellowish nodules on the hairs.
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CUTANEOUS
•caused by fungi that infect only the
superficial keratinized tissue (skin, hair, and
nails)/cannot grow at 37degrees
•Dermatophytes eg
microsporon/trichophyton/epidermophyton
•Sometimes reffered as Ringworm – skin lesions
characterized by red margins, scales and itching
•Image?
…CUTANEOUS MYCOSES
•Classified based on location of infectiona) Tinea pedis – on the feet or between the toesb) Tinea corporis – between the fingers, in wrinkles
on the palms c) Tinea cruses – lesions on the hairy skin around
the genitaliad) Tinea capitis – scalp and eyebrows
e) Onychomycosis – chronic infection of the nail bed
•Commonly seen in toes•Hyperkeratosis – extended scaly areas on the hands and feet
Microbiology: A Clinical Approach © Garland Science
..CUTANEOUS
www.doctorfungus.org
Mucocutaneous …
•MUCOCUTANEOUS MYCOSES colonization of
the mucous membranes
•Caused by the yeast Candida albicans
•Often associated with a loss of
immunocompetence
•Thrush – fungal growth in the oral cavity
•An indicator of immunodeficiency.
•Vulvovaginitis – fungal growth in the vaginal
canal
•Can be associated with a hormonal
imbalance
SUBCUTANEOUS MYCOSES
•Agent –from the soil /vegetable
•Entry-through trauma
•localized primary infections of
subcutaneous tissue:
•Can cause the development of cysts and
granulomas.
•Provoke an innate immune response -
eosinophilia.
SUBCUTANEOUS MYCOSES
There are several types:•Sporotrichosis – traumatic implantation of fungal
organisms
•Paranasal conidiobolae mycoses– infection of the
paranasal sinuses
•Causes the formation of granulomas.
•Zygomatic rhinitis– fungus invades tissue through
arteries
•Causes thrombosis.
•Can involve the CNS.
SUBCUTANEOUS MYCOSES• At ambient environmental temp-mould
• At 35-37degrees grow as budding yeast
• Sporothrix schenckii -Sporotrichosis
• Phialophora verrucosa, Fonsecaea pedrosoi, others - Chromoblastomycosis
• Pseudallescheria boydii, Madurellamycetomatis, others - Mycetoma
• Exophiala, Bipolaris, Exserohilum, and others -Phaeohyphomycosis
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DEEP/systemic MYCOSES
Deep mycoses Usually seen in immunosuppressedpatients with:
•AIDS•Cancer•Diabetes
•Can be acquired by:•Inhalation of fungi or fungal spores•Use of contaminated medical equipment
•Deep mycoses can cause a systemic infection –disseminated mycoses
•Can spread to the skin
Common examples
• Coccidioides immitis, C posadasii -Coccidioidomycosis
• Histoplasma capsulatum- HistoplasmosisBlastomyces dermatitidis -Blastomycosis
• Paracoccidioides brasiliensis -Paracoccidioidomycosis
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Microbiology: A Clinical Approach © Garland Science
..DEEP MYCOSES
www.doctorfungus.org
..DEEP MYCOSES
Coccidiomycoses – caused by genus Coccidioides
•Primary respiratory infection
•Leads to fever, erythremia, and bronchial
pneumonia
•Usually resolves spontaneously due to immune
defense
•Some cases are fatal
…DEEP MYCOSES
Histoplasmosis – caused by Histoplasma
capsulatum
•Often associated with immunodeficiency
•Causes the formation of granulomas
•Can necrotize and become calcified
•If disseminated, histoplasmosis can be fatal.
Microbiology: A Clinical Approach © Garland Science
..DEEP MYCOSES
© CDC/Susan Lindsley, VD
…DEEP MYCOSES
Aspergillosis – caused by several species of
Aspergillus
•Associated with immunodeficiency
•Can be invasive and disseminate to the blood
and lungs
•Causes acute pneumonia
•Mortality is very high.
•Death can occur in a matter of weeks.
opportunistic mycoses eg.1. Candida albicans and other Candida species -
Systemic candidiasis
2. Cryptococcus neoformans- Cryptococcosis
3. Aspergillus fumigatus and other Aspergillusspecies -Aspergillosis
4. Species of Rhizopus, Absidia, Mucor, and other zygomycetes - Mucormycosis (zygomycosis)
5. Penicillium marneffei- Penicilliosis
Candidiasis
Cause: Candida albicans
–Dimorphic fungus of the class Deuteromycetes
–Grows as yeast or pseudohyphae
– Spread by contact; often part of normal flora
–Opportunistic infections common
–Vulvovaginitis
–Oral candidiasis (thrush)
– Intestinal candidiasis
Candidiasis
Cutaneous
Thrush
Vaginal candidiasis is the most common clinical infection. Local factors such as pH and glucose concentration (under hormonal control) are of prime importance in the occurrence of vaginal candidiasis. In mouth: normal saliva reduces adhesion (lactoferrin is also protective).
Chronic mucocutaneouscandidiasis
Chronic mucocutaneous
candidiasis (CMC) is the label
given to a group of overlapping
syndromes that have in common
a clinical pattern of persistent,
severe, and diffuse cutaneous
candidal infections. These
infections affect the skin, nails
and mucous membranes.
Immunologic studies of patients with
CMC often reveal defects related to
cell-mediated immunity, but the
defects themselves vary widely.
Mucutaneous candidiasis: response to fluconazole
Transfusion of a Candida-specific transfer factor has
been reported to be very successful (remission for > 10
years) when combined with antifungal therapy. The
availability of effective oral agents, especially the azole
antimicotics, has dramatically changed the life of
patients living with CMC.
Cryptococcosis
Respiratory Fungal Infection
–Cryptococcus neoformans
–A yeast of class Basidiomycetes
– Soil; esp. contaminated with bird droppings
–Airborne to humans
–Gelatinous capsules resist phagocytosis
–Respiratory tract infections
–Occasional systemic infections involving brain & meninges
Opportunistic Mycoses
•Opportunistic mycoses are fungal infections that do not
normally cause disease in healthy people, but do cause
disease in people with weakened immune defenses.
•The most common infections are:
•Candidiasis
•Aspergillosis
•Cryptococcosis
•Zygomycosis
•Pneumocystis carinii
Cryptococcus neoformans
• Primary infection in lungs
• Cryptococcal meningitis is most common disseminated manifestation
• Can spread to skin, bone and prostate
Organism is ubiquitous and infections
occur worldwide
C. neoformans recovered in large
amounts in pigeon poop
Does not cause disease in birds
Diagnosis
• Lumbar puncture and microscopic examination of cerebrospinal fluid is diagnostic.
• (India ink staining)
Cyrptococcal antigens in CSF and serum.
Immune response
Phagocytosis by neutrophils is inhibited by the presence of a capsule.
However, activated neutrophils have an increased capacity to
phagocytize C. neoformans.
Cell mediated immunity primary defense
About 30% of cryptococcus infections occur in patients with lymphoma
(CNS)
Therapy
Amphotericin B & 5FC
Fluconazole also effective
Aspergillosis
• Genus occurs worldwide and contains hundreds of species.
• These species constitute the most commonly found fungi in any environment
Major portal of entry is the
respiratory tract. Dissemination
can occur from the lungs and
involve other areas of the lung,
the brain, GI tract, and kidney.
CNS and nasal-orbital cavities
can also occur without lung
involvement. Risk factors for
invasive disease are
neutropenia and high doses of
Aspergillosis• Aspergillosis is the most common fatal infection seen in patients with chronic
granulomatous disease of childhood.
• Patients with this condition are unable to form toxic oxygen radicals after phagocytosis.
• Progressive and disseminated disease can complicate neoplastic diseases, especially acute leukemia, bone marrow and organ transplantation (not necessarily AIDS).
In immunosuppressed hosts:
invasive pulmonary infection, usually
with fever, cough, and chest pain.
May disseminate to other organs,
including brain, skin and bone. In
immunocompetent hosts: localized
pulmonary infection in persons with
underlying lung disease. Also causes
allergic sinusitis and allergic
bronchopulmonary disease.
Agent: Aspergillus fumigatus, A. flavus.
Environmental species kill neutropenicpatients.
• Zygomycosis. Zygomycosis due to Rhizopus, Rhizomucor, Absidia, Mucor species, or other members of the class of Zygomycetes, also causes invasive sinopulmonary infections. An especially life-threatening form of zygomycosis(also known as mucormycosis), is known as the rhinocerebral syndrome, which occurs in diabetics with ketoacidosis. In addition to diabetic ketoacidosis, neutropenia and corticosteroids are other major risk factors for zygomycosis.
• Phaeohyphomycosis. Phaeohyphomycosis is an infection by brown to black pigmented fungi of the cutaneous, superficial, and deep tissues, especially brain. These infections are uncommon, life-threatening, and occur in various immunocompromised states.
• Hyalohyphomycosis. Hyalohyphomycosis is an opportunistic fungal infection caused by any of a variety of normally saprophytic fungi with hyaline hyphalelements. For example, Fusarium spp. infect neutropenic patients to cause pneumonia, fungemia, and disseminated infection with cutaneous lesions.
…. Respiratory Fungal Infections
Histoplasmosis
–Histoplasma capsulatum, an ascomycete
–Airborne infection
– Transmitted by inhalation of spores in contaminated spores
–Associated with chicken & bat droppings
–Respiratory tract symptoms; fever, headache, cough, chest pains
….Respiratory Fungal Infections
Blastomycosis
–Blastomyces dermatitidis, an ascomycete
–Associated with dusty soil & bird droppings
– Skin transmission: via cuts & abrasions
–Raised, wart-like lesions
–Airborne transmission: via inhalation of spores
–Respiratory tract symptoms
–Occasional internal infections with high fatality rate
Aflatoxin are a small group of mycotoxins
produced by the fungi from the genus
Aspergillus, Aspergillus flavus and
Aspergillus parasiticus , produces a natural
occurring human carcinogen, bis-
furanocumarin that is found in aflatoxin,
. Aflatoxins are known contaminants on
corn, peanuts, tree nuts, cottonseed
and certain meats and hypoallergenic
milks
Useful Properties of Fungi
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Source of food e.g. mushrooms
Fermentation - Production of
alcohol, bread, cheese
e.g. Sacchromyces spps
Antibiotic production
e.g. Penicillin from
Penicillium notatum
Useful Properties of Fungi
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Ergot from Claviceps
purpurea, used to induce
uterine contractions
Vaccines for Hepatitis B –
Sacchromyces cerevisiae
Diagnosis/Treatment
1. Grown in medium that selects for fungal growth-Grow at 25 C and 37 C
2. KOH preparations of skin biopsies-Dissolves keratin in skin scrapings or biopsies
-Leaves only fungal cells
3. Therapy- amphotericin B or ketoconazole-Toxic to humans
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The end
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