Exam 2: Intro to Fungi and Parasites Flashcards
Fungi
Characteristics
- Kingdom ⇒ Myceteae
- Cell walls ⇒ chitin
- Cell membrane ⇒ ergosterol
- Classified as yeast or mycelium
- Yeast ⇒ unicellular
- Mycelium ⇒ multicellular
Fungi cell walls are made mostly of…
chitin
(N-acetylglucosamine + glucan)
Yeast
- Unicellular
- Replicate by budding, fission, or molds
Mycelium
- Multicellular
- Formed from hyphae
- Each is unicellular
- Hollow or divided by crosswalls
- Non-septate vs septate
- Hyphae grow together forming a mat ⇒ mycelium
Fungi
Reproduction
Occurs sexually or asexually.
-
Asexually
- Via production of various spores
- Conidia
- Sporangia
- Ascospores
- Spores disperse and start new colonies
- Via production of various spores
- Sexual process not well understood
Fungi
Metabolism
- Most are free living
- Aerobic
-
Heterotrophs
- Obtains carbons from organic matter
- Most are saprophytic
- Obtain nutrients from dead organic matter
- Some are normal human flora
- Candida, Malassezia
- Some are highly adapted mammalian or human parasites
- Dermatophytes, Pneumocytis
Fungi
Classification
May be organized based on tissues infected:
- Cutaneous
- Subcutaneous
- Systemic or endemic
- Opportunistic
Cutaneous Fungi
- Cause infections of the keratinized layer of the skin, hair, and nails
- Termed dermatophytes
Subcutaneous Fungi
- Infect the dermis, subcutaneous tissue, bone, or cornea
- Ex. Sporothrix
Systemic or Endemic
Fungi
- Causes systemic disease
- Confined to specific geographic regions
-
Dimorphic
- Two lifecycle forms
- Usually cause primary infection in the lung with subsequent dissemination
- Transmission via inhalation of spores
Opportunistic Fungi
- Human commensals or fungi found in the environment
- Affect immunocompromised individuals
- Can cause serious disease
- Ex. Candida
Fungi
Transmission
Varied routes of infection.
Includes:
- Respiratory
- Direct contact
- Soil-contaminated wounds
Fungi
Pathogenesis
-
Some are pathogenic to normal hosts
- Have overt virulent factors
- Ex.
- Coccidioides
- Histoplasma
-
Most are opportunists
- Minimal virulence
- Must have pre-disposing conditions to cause disease
- Loss of normal bacterial flora
- Iatrogenic immunosuppression
- Genetic or acquired immunodeficiencies
- DM
- Mechanical breach of skin/mucosal surfaces
- Indwelling catheter
- Serious disease is not common in immunocompetent host
Fungal
Immunity
- Responses vary with type
-
Innate immunity to most fungi is very high
-
Neutrophil killing is the primary mechanism
- Esp. against hyphae
- Line up along hyphal surfaces and secrete lysosomal enzymes
- Conidia/spores requires Mφ ingestion
-
Neutrophil killing is the primary mechanism
-
Intracellular forms ⇒ yeast
- Requires cell mediated immunity for elimination
- CMI important in most fungal infections
- Impaired CMI / low T-cell counts ↑ susceptibility to invasive fungal infections
- Ab with minor role in resistance to fungi
Fungi Propagation
- Can be propagated on any nutrient medium
-
Mold forms ⇒ Sabaraud’s Dextros Agar (SDA)
- Growth of mold forms
- ID of spores (conidia)
- Low pH inhibits bacterial colonization
- Also includes some anti-bacterial agents
- Commonly takes 1-4 weeks to grow @ 25° C
-
Yeast forms cultivated at 37° C on specialized media
- Cutaneous forms frequently visualized in tissue specimens w/ KOH
- Can use lactophenol cotton blue to stain
Fungal
Treatments
- # of available treatments limited
- Due to common pathways and metabolic processes b/t fungi & mammalian cells
- Risk of toxicity high
Aspergillus
Overview
-
Aspergillus fumigatus and Aspergillus flavus
- Most commonly associated with invasive disease
- Opportunistic fungi
- Disease usually associated with severe neutropenia
- Found ubiquitously in the environment
- Infection is acquired exogenously
Aspergillus
Morphology
- Exist as molds
- Composed of septate hyphae
- Branches @ 45° angles ⇒ dichotomous branching
- Characteristic of Aspergillus
- Reproduce asexually by conidiaphore formation
Aspergillus
Transmission
Spread by inhalation of conidiaspores
No person to person transmission
Allergic Aspergillosis
- Seen in people with chronic asthma or CF
- Symptoms
- Episodic wheezing, fever, eosinophilia
- Transient pulmonary infiltrates
- May become severe with age
- Can lead to fibrosis
Aspergilloma
-
Usually seen in those with underlying lung diease
- Particularly those with pre-existing cavities in the lung
- Non-allergic colonization
- Chronic process with development of pathological changes in the lung
- Formation of Aspergillus containing granulomas
- Causes “fungus ball” formations on CXR
- Granulomas must be surgically removed + antifulgal medications
Systemic or Invasive
Aspergillosis
-
Only in immunocompromised individuals
- Risk factor ⇒ neutropenia
- May involve pulmonary, sinus, cerebral, or cutaneous sites
- Pathogenesis involves angioinvasion, thrombosis, and dissemination to other organs
- Damage caused by tissue infarcts, hemorrhage, and necrosis
Aspergillus
Diagnosis
-
Gomeri silver stain of tissue sections
- ID by dichotomously branched (45° angle) septate hyphae
- Isolation in culture on Sabaraud’s Dextrose Agar (SDA)
-
Allergic aspergillosis
- Elevated specific IgE
- Eosinophilia
- Positive skin test (Type I) to Aspergillus Ag
Aspergillus
Immunology
- Conidia (inhaled) ⇒ Mφ
- Hyphae ⇒ neutrophils
- Line up along hyphal walls and secrete lysosomal enzymes
- Patrol blood vessels
- Aspergillus is an angioinvasive organism
- Neutropenia is the #1 risk factor for invasive aspergillosis
Aspergillus
Treatment
Amphotericin B for invasive aspergilliosis
Surgical removal of aspergilloma
Parasites
Overview
- Refers specifically to invertebrate animals that infest humans and other animals
-
Causes massive morbidity and mortality in developing countries
- Many have specific geographic distribution
- Some with large distribution
- Developed and undeveloped countries
Definitive Hosts
Species in which the parasite undergoes sexual reproduction.
Intermediate Host
Species in which a part or the whole process of asexual reproduction occurs.
Incidental Host
Unnatural host to which the parasite may not be adapted for replication.
Leads to unusual pathology.
Vectors
Species capable of transmitting the parasite from one host to another.
Trophozoite
Lifecycle form that grows and replicates by binary fission within the host.
Cyst
Lifecycle form that is:
- Dormant
- Non-replicating
- Resists environmental extremes
- Frequently transmitted between hosts
Protozoa
- Unicellular microbes
- Range in size from 2-100 microns
- Have a cell membrane and numerous organelles
- Organs of motility vary
- Includes:
- Flagellates
- Amoeba
- Ciliates
- Sporozoa
Flagellates
- Cyst and trophozoite forms
- Have flagella
Amoeba
- Cyst and trophozoite forms
- Form pseudopods
- Temporary arm-like projection of a eukaryotic cell membrane that are developed in the direction of movement
Ciliates
- Cyst and trophozoite forms
- Have cilia
Sporozoa
- Frequently intracellular pathogens
- Many forms:
- Trophozoite
- Sporozoite
- Motile spore-like stage in the life cycle
- Cysts
- Gametes
Fungi
- Protozoa reclassified as degenerate fungi
- Cell walls of chitin
- Produces spores
Microsporidia
Obligate intracellular forms
Helminths
Multicellular worms
Nematodes
Round
Teeth or plates for attachment
Trematodes
Flukes
Oral and ventral suckers
Cestodes
Flat, segmented body (proglottids)
Hooks or suckers for attachment
Ex. hook worm
Parasite
Epidemiology
More prominent in tropical/subtropical regions
Parasite
Transmission
Always acquired exogenously by multiple means:
- Direct penetration
- Insect vector
- Food borne
Parasite
Pathogenesis
Virulence factors:
- Exotoxins
- Hydrolytic enzymes
- Proteinases
- Migration through tissue
- Mechanical blockage
- Nutritional depletion
Host-Parasite
Interactions
-
Most parasitic infections are chronic
- Some can live within a host for more than a decade
- May induce pathology by hypersensitivity to parasite products and/or autoimmunity
- May induce nutritional depletion
Parasite
Host Defense Avoidance
- Ag variations
- Camouflage
- Acquisition of host Ag
- Intracellular infection
- Suppression or redirection of host immune response
- Encystation
- Escape from phagosomes or phagocytic mechanisms
- Protective cuticles
- Helminthes only
Parasitic Infection
Diagnosis
- Most dx by ID of parasite or progency in clinical specimens
- Cysts, eggs, larvae, worms
- Understanding life cycle critical to effective dx
