fungal infections Flashcards
biology of fungi
eukaryotic
chitinous cell wall
heterotrophic
how do fungi move
by means of growth or through the generation of spores which are carried through air or water
what is yeast
yeasts are small single called organisms that divide by budding
what % of fungal species are yeast
yeast account for <1% of fungal species
describe moulds
moulds form multicellular hyphae and spores
some fungi exist as both yeasts and mould switching between the two when conditions suit - dimorphic fungi
how many species of fungi are there
5 million
but only a few hundred have been reported as causing human infection
why do only a few hundred fungi affects humans
because they are unable to grow at 37 degrees
and because of the innate and adaptive immune response
are there lots of anti fungal drugs
no there are limited options
describe dna/rna synthesis of fungi
its similar to mammalian
via protein synthesis
describe fungal cel wall
mannoproteins
B1,3 glucan
B1,6 glucan
chitin
doesn’t exist in humans
describe fugal cell membrane
contains ergosterol
human cell membrane contains cholesterol not ergosterol
what drugs affect dna synthesis in fungi
flucytosine
griseofulvin
which drugs affect fungal cell wall
echinocandins
which drugs affect plasma membrane of fungi
polyenes eg amphotericin
azores
allylamines eg terbinafine
which fungal ifnection is very common
superficial fungal infection
which fungal ifnection is rare
invasive fungal infection
it’s rare but its easily missed
are life threatenig fungal infections common
no
life threatening fungal infection is rare in healthy hosts
but most people would have had normal fungal infections
what are dimorphic fungi
Some fungi exist as both yeasts and moulds switching between the two when conditions suit
what is mucosal candidiasis
a common and recurrent disease that causes significant morbidity
risk factors for mucosal candidiasis
immunosuppresion
diabetes
antibacterial therapy
mucosal disruption
treatment for mucosal candidiasis
topical or oral azoles
impact of resistance on mucosal candidiasis
resistant disease is common in recurrent cases
acquired resistance in normally susceptible species
selection for intrinsically resistant species
what are dermatophyte infections due to
trichophyton spp
microsporum spp
epidermophyton floccosum
how can you get dermatophyte infections
human-human or animal-human transmittion
treatment for dermatophyte infections
usually with topical or oral azoles
or
terbinafine
examples of dermatophyte diseases
tines capitis
tines corporis
tinea cruris
tinea unguium
tinea pedis
is ringworm a worm
no
how do dimorphic fungi cause disease
they can cause severe infection in healthy hosts in endemic areas
infection via inhalation of conidia from soil or implantation
what temp do dimorphic fungi mould at
ambient temp
25-30 C
when do dimorphic fungi convert to yeast form
at 37C
occurs in response to heat related stress on organism
what does ‘true pathogens’ refer to
infect healthy hosts
what diseases can coccidioides cause
asymptomatic/ sub clinical ifne3ction is common
most of rest - community acquired pneumonia
severe disease - respiratory failiure or septic shock
late disease - does not correlate with severity of initial smtooms
late manifestations of coccidioides
cavitatory lung disease
orthopaedic
cutaneous ulcers and abscesses
cervical lymphadenopathy
intracranial - chronic meningitis s
describe NHS anti fungal spend
> £150m/year
much of this cost is prophylaxis or empirical treatment of possible invasive fungal disease due to poor diagnostics
what does fungal diagnosis usually rely on
relies on it being in the differential
what is invasive candidiasis
a disease that is mostly due to ifnection of prosthetic devices or intra and abdominal disease
what does cryptococcus cause
acute or chronic meningitis in patients with reduced cell mediated immunity
differential diagnosis of sub/acute chronic meningitis
• Infective
– Tuberculosis
– Cryptococcus
– Dimorphic fungi – Histoplasma, Coccidioides, Blastomyces
– Lyme
– Brucella
– Syphilis
• Non-infective
– Sarcoidosis
– Behçets’s
– SLE
– Malignant
– Drug induced
treatment for cryptococcus
liposomal amphotericin B and flucytosine with maintenance fluconazole
are mucorarecous moulds common
no they are rare but cause rapidly progressive infections that cross tissue planets
what is the aim of anti microbial drug therapy
to achieve inhibitory levels of agent at the site of infection without host cell toxicity
what does antimicrobial drug therapy rely on
upon identifying molecules with selective toxicity for organism targets
what are organism targets for antimicrobial drug therapy
Target does not exist in humans
Target is significantly different to human analogue
Drug is concentrated in organism cell with respect to humans
Increased permeability to compound
Modification of compound in organism or human cellular environment
Human cells are ‘rescued’ from toxicity by alternative metabolic pathways
is severe fungal disease commo in healthy people
no Severe disease is caused by a small number of fungi in the immunocompromised
Fungal infection can be the initial presentation of the underlying disease
why are fungi difficult to treat
because we have relatively few classes of agent effective against them
