Difference between revisions of "Fungi"
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| + | {{review}} | ||
| + | {{toplink | ||
| + | |backcolour = FFE4E1 | ||
| + | |linkpage =Immunology - WikiBlood | ||
| + | |linktext =IMMUNOLOGY | ||
| + | |sublink1 =Host invasion by microorganisms - WikiBlood | ||
| + | |subtext1 =HOST INVASION BY MICROORGANISMS | ||
| + | |sublink2 =Fungi | ||
| + | |subtext2 =INFECTIOUS AGENTS AND PARASITES | ||
| + | |pagetype =Blood | ||
| + | }} | ||
| + | =Introduction= | ||
| − | + | Although there are over 50,000 identified species of fungi, only a few hundred are known to be pathogenic, causing infections known as '''mycoses''' (mycology being the study of fungi). Fungi are nonphotosynthetic organisms which are restricted to a parasitic or saphrophytic exsistence. They are abundant in soil, vegetation, water and on decaying vegetation and wood. Fungi have a eukaryotic cell structure and are able to grow as branching or filamentous forms (mycelia) or as single cells (yeasts). | |
| + | |||
| + | =Types of Fungi= | ||
| + | |||
| + | There are two principle types of fungi, the moulds and the yeasts. Fungal '''hyphae''' are the branching tubular structures of moulds which become entwined as the fungi grows to form a '''mycelium'''. Hyphae are divided by cross walls into '''septa'''. There are arial (above the surface) and surface hyphae. The aerial hyphae produce spores which are reproductive fungal cells. There are two main types of spore produced, '''conidiospores''' and '''sporangiospores'''. These produce asexual spores called '''conidia''' which are relatively resistant to physical and chemical agents. | ||
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| + | The yeasts range from 3µm to 5µm and are oval or spherical cells. '''Pseudohyphae''' are produced by some yeasts which are chains of irregular yeast cells. '''Dimorphic fungi''' change from the mycelial form into yeasts in certain conditions, e.g. 37°C or when inside animal tissue. | ||
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| + | =Fungal Reproduction= | ||
| + | |||
| + | The majority of fungal reproduction is asexual. There is three main methods by which fungi reproduce asexually: | ||
| + | |||
| + | 1.Sporulation followed by spore germination | ||
| + | *E.g. ''Aspergillus'' | ||
| + | |||
| + | 2. Fragmentation of hyphae | ||
| + | |||
| + | 3. Budding of yeast cells | ||
| + | *E.g. ''Candida'' and ''Cryptococcus'' | ||
| + | |||
| + | =Major pathogenic fungi= | ||
| + | '''Superficial''': These infections affect only the skin, hair, nails etc. | ||
| + | *Generally not dangerous | ||
| + | *Examples- ''Hortaea werneckii'', causing tinea nigra, and ''Piedraia hortae'', causing black piedra | ||
| + | |||
| + | '''Cutaneous''': Also known as [[Dermatophytosis|'''dermatophytoses''']] | ||
| + | *Only affect superficial keratinized tissue- skin, hair and nails | ||
| + | *Again generally not dangerous | ||
| + | *Examples- ''Candida albicans'', causing candidiasis of the skin and nails, ''Microsporum'' species | ||
| + | |||
| + | [[Subcutaneous Mycoses|'''Subcutaneous''']]: Usually cause chronic localised infections of the skin and underlying dermis | ||
| + | *Normally reside in soil and vegetation; they enter skin through cuts and grazes | ||
| + | *Can occasionally affect the deep tissues, e.g. bones and muscles | ||
| + | *Examples- ''Sporothrix schenkii'', causing sporotrichosis, ''Madurella mycetomatis'' causing mycetoma | ||
| + | |||
| + | [[Systemic Mycoses|'''Systemic''']]: Also known as '''deep''', '''endemic''' or '''primary''' | ||
| + | *Usually serious; sometimes fatal | ||
| + | *Examples- ''Histoplasma capsulatum'' causing histoplasmosis, ''Blastomyces dermatitidis'' causing blastomycosis | ||
| + | |||
| + | '''Opportunistic''': Ubiquitous fungi that affect only susceptible hosts; immunocompetent individuals are normally resistant | ||
| + | *Examples- ''Aspergillus fumigatus'', causing aspergilliosis, ''Cryptococcus neoformans'', causing cryptococcosis | ||
| + | |||
| + | =Immunity to fungi= | ||
| + | Cutaneous and superficial fungal infections are normally self-limiting, with recovery associated with a resistance to re-infection. As hosts often develop delayed-type hypersensitivity, this resistance appears to be cell-mediated. | ||
| + | *T cell immunity- it is thought that helper T cells release cytokines to activate macrophages to fight the infection | ||
| + | *Neutrophils- there is now growing evidence for the role of neutrophils in some infections of the respiratory system, with defensin and the nitric oxide pathways implicated | ||
Revision as of 10:47, 23 April 2009
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Introduction
Although there are over 50,000 identified species of fungi, only a few hundred are known to be pathogenic, causing infections known as mycoses (mycology being the study of fungi). Fungi are nonphotosynthetic organisms which are restricted to a parasitic or saphrophytic exsistence. They are abundant in soil, vegetation, water and on decaying vegetation and wood. Fungi have a eukaryotic cell structure and are able to grow as branching or filamentous forms (mycelia) or as single cells (yeasts).
Types of Fungi
There are two principle types of fungi, the moulds and the yeasts. Fungal hyphae are the branching tubular structures of moulds which become entwined as the fungi grows to form a mycelium. Hyphae are divided by cross walls into septa. There are arial (above the surface) and surface hyphae. The aerial hyphae produce spores which are reproductive fungal cells. There are two main types of spore produced, conidiospores and sporangiospores. These produce asexual spores called conidia which are relatively resistant to physical and chemical agents.
The yeasts range from 3µm to 5µm and are oval or spherical cells. Pseudohyphae are produced by some yeasts which are chains of irregular yeast cells. Dimorphic fungi change from the mycelial form into yeasts in certain conditions, e.g. 37°C or when inside animal tissue.
Fungal Reproduction
The majority of fungal reproduction is asexual. There is three main methods by which fungi reproduce asexually:
1.Sporulation followed by spore germination
- E.g. Aspergillus
2. Fragmentation of hyphae
3. Budding of yeast cells
- E.g. Candida and Cryptococcus
Major pathogenic fungi
Superficial: These infections affect only the skin, hair, nails etc.
- Generally not dangerous
- Examples- Hortaea werneckii, causing tinea nigra, and Piedraia hortae, causing black piedra
Cutaneous: Also known as dermatophytoses
- Only affect superficial keratinized tissue- skin, hair and nails
- Again generally not dangerous
- Examples- Candida albicans, causing candidiasis of the skin and nails, Microsporum species
Subcutaneous: Usually cause chronic localised infections of the skin and underlying dermis
- Normally reside in soil and vegetation; they enter skin through cuts and grazes
- Can occasionally affect the deep tissues, e.g. bones and muscles
- Examples- Sporothrix schenkii, causing sporotrichosis, Madurella mycetomatis causing mycetoma
Systemic: Also known as deep, endemic or primary
- Usually serious; sometimes fatal
- Examples- Histoplasma capsulatum causing histoplasmosis, Blastomyces dermatitidis causing blastomycosis
Opportunistic: Ubiquitous fungi that affect only susceptible hosts; immunocompetent individuals are normally resistant
- Examples- Aspergillus fumigatus, causing aspergilliosis, Cryptococcus neoformans, causing cryptococcosis
Immunity to fungi
Cutaneous and superficial fungal infections are normally self-limiting, with recovery associated with a resistance to re-infection. As hosts often develop delayed-type hypersensitivity, this resistance appears to be cell-mediated.
- T cell immunity- it is thought that helper T cells release cytokines to activate macrophages to fight the infection
- Neutrophils- there is now growing evidence for the role of neutrophils in some infections of the respiratory system, with defensin and the nitric oxide pathways implicated