pathogenesis of infectious disease Flashcards
list 4 possible ocular diseases/infections from ascending order of severity that can be caused by pathogens
- periocular and orbital
- keratitis
- uveitis
- endophthalmitis
what can the exposed condition of the ocular service implicate about disease and how does this not happen as often as thought
the exposed condition of the ocular surface means it is frequently in contact with disease causing micro-organisms, however the ocular surface has many defence mechanisms to ensure that it remains disease free including:
- anti-microbial properties of the tears
- constant shedding of the cells from the ocular surface
these reduce contact time with the pathogen and a number of affective immunological mechanisms
name 3 risk factors that can predispose the eye to infections
- patients immune status
- ocular morbidity
- contact lens wear
list 5 potential pathogens that can cause infection of the cornea
- bateria
- HSV
- VZV
- protozoa
- fungi
list 4 potential pathogens that can cause infection of the uvea
- bacteria
- CMV
- VZV
- protozoa
list 2 potential pathogens that can cause endophthalmitis
- bacteria
- fungi
which potential pathogen can cause infection of the orbit
bacteria
list 5 potential pathogens that can cause infection of the lids and conjunctiva
- bacteria
- chlamydia
- adenovirus
- HSV
- VZV
what are the 2 least common pathogens to affect the eye
fungi and protozoa
where in the eye are microbial flora usually present and since when
- on the eyelids and in the conjunctiva sac
- from birth and are present throughout the life
what are these harmless microbial flora called
commensals
what type of non-pathogenic microbes make up the microbial flora and which microbes less commonly make up the microbial flora
- most commonly gram +ve bacteria
- less commonly environmental fungi and viruses
which parts of the eye are there no microbes/commensals at all
- cornea
and - anterior chamber
are sterile
what do the commensals found on the eyelid and conjunctiva form
part of the innate defence system of the eye, they compete with potential pathogens for essential nutrients
what 3 classes of bacteria make up the normal conjunctival and eyelid flora
- gram +ve cocci (sphere shape)
- gram +ve bacilli (rod shaped)
- anaerobic
list the 3 types of gram +ve cocci commensal bacteria
- staphylococcus epidermis 30-80%
- staphylococcus aureus 3-25%
- micrococcus sp. 1-28%
which bacterial commensal accounts for 30-80% of the conjunctiva and lids
gram +ve staphylococcus epidermis
which bacterial commensal accounts for 3-25% of the conjunctiva and lids
gram +ve staphylococcus aureus
which bacterial commensal accounts for 1-28% of the conjunctiva and lids
gram +ve micrococcus
what is the name of the gram +ve bacilli commensal bacteria found on the conjunctiva and lids
corynebacterium species 5-83%
which gram +ve bacterial commensal accounts for 5-38% of the conjunctiva and lids
grame +ve bacilli corynebacterium species
what is the name of the anaerobic commensal bacteria found on the conjunctiva and lids
propionibacterium sp. 0-33%
which bacterial commensal accounts for 0-33% of the conjunctiva and lids
propionibacterium (anaerobic)
when can all the commensal bacteria found on the conjunctiva and eyelids cause disease
in particular circumstances when they are found in high concentration
list three peri ocular structures which can get infected
- eyelids
- conjunctiva
- lacrimal system
name 2 orbital infections
- orbital cellulitis
- pre septal cellulitis
name a peri-ocular infection of the eyelid
external hordoleum (stye)
what is a external hordoleum (stye) found on the eyelid an infection of
- the ciliary sebaceous gland (zeis)
- typically staph. aureus
what form of treatment is needed to treat a external hordoleum (stye)
most commonly warm compresses
topical antibiotics if needed
what else has to be affected as well as the gland of zeis for the infection to be a internal hordoleum
meibomian glands
what are the signs and symptoms associated with a external hordoleum (stye)
- lid swelling
- lid tenderness
- collection of pus under the skin
name a peri-ocular infection of the eyelid other than a external hordoleum (stye)
blepharitis - inflammation of the eyelids
what are the 2 forms of blepharitis
chronic or remitting
what 2 aetiologies can blepharitis have
infective or non-infective (often)
what are the 2 infectious organisms that cause blepharitis
- staph, aureus
- staph epidermis
what is the treatments of blepharitis
- eyelid hygiene alone
- may require topical antibiotics
what are the characteristics of the staphylococci bacteria
- commensals of human skin
- gram +ve cocci (clumps)
- grow on most media
what is the spectrum of disease caused by staphylococci bacteria
- can be local such as conjunctivitis or deep infection as it can penetrate into deeper tissues
- can cause toxin mediated disease, where it produces damage primarily through the production of toxins which are cytotoxic for cells and can cause harm
what are the signs of pre septal cellulitis that differentiates it from orbital cellulitis
normal vision and no pupillary defect
what are the signs of orbital cellulitis that differentiates it from pre septal cellulitis
- ophthalmoplegia (down and out)
- pupillary defect/RAPD
- proptosis
- pain
- painful eye movements
what can orbital cellulitis arise from
abscess in the ethmoid sinus and less commonly the maxillary and frontal, which spreads into the orbit
who is orbital cellulitis more commonly found in
children
where can the infection of orbital cellulitis spread to which makes it sight and life threatening
to the cranial cavity
as there is direct connection between the orbit and the cranium
where does the septum run
from the orbital margins to the tarsal plates
how many orbital infections does pre septal cellulitis account for
94% (most common)
how many orbital infections does orbital cellulitis account for
6%
what is pre septal cellulitis and orbital cellulitis both more common in and why how much
in children 75% in
what are the 2 aetiologies of pre septal cellulitis
- sinusitis in 80-90% of cases
- strep. pneumoniae / H.influenza
what is used in the diagnosis of an orbital infection
CT scan is the most helpful in DDX
what is the treatment for pre septal cellulitis
antibiotics
against potential causative organisms such as, staph aureus, strep pneumonia or H. influenza
what is the treatment for orbital cellulitis
drainage of abscess and concurrent IV antibiotics
name the 3 characteristics of the bacteria streptococci
- commensals of mouth/gut
- gram +ve cocci (chains)
- grows on blood agar (haemolysis)
what is the spectrum of disease of the bacteria streptococci
- wide
- local (conjunctivitis) to systemic infections (pneumonia or meningitis)
- toxin mediated disease
what distant appearance does the bacteria streptococci cause on an agar plate
they cause a clear zone called haemophilus
what are three characteristics of haemophilus spp
- commensal of URT
- gram negative rod
- fastidious (grows on chocolate agar = a variant of blood agar)
haemophilus spp are ____________ pathogens who live in the ______ without causing __________ but with reduced __________ functions or ___________ inflamed tissues cause _____________ for it to cause ___________
haemophilus spp are opportunistic pathogens who live in the host without causing disease but with reduced immune functions or chronically inflamed tissues cause opportunity for it to cause infection
what is the spectrum of disease of the bacteria haemophilus spp
- much less since vaccination
- local infection (sinitis or conjunctivitis) to meningitis or pneumonia
which group of patients is conjunctivitis most common in
children
which 3 pathogens can present as conjunctivitis
- viral
- bacterial
- chlamydial
what evaluation is often not done with conjunctivitis and why
lab can be done but isn’t done as much because conjunctivitis is self limiting
when will you carry out a scraping/swab of conjunctivitis on a patient and why
only done on ophthalmia neonatorium (if contract in 1st month of life) as they need to be referred for intensive treatment
what type of conjunctivitis do girl and chlamydial pathogens cause
characteristic follicular conjunctivitis
what are the characteristics of bacterial conjunctivitis
- incidence is unknown
- rapid onset
- unilateral, but bilateral after 1-2 days
name the bacteria involved acute in conjunctivitis in adults and children
staphylococcus aureus
name the bacterias involved in acute conjunctivitis in children only
- strep. pneumo
- H. influenza
name the bacteria involved in chronic conjunctivitis
- due to endotoxins
- staphylococcus aureus
- moraxella
- enterobacteriacae
what may be difficult with chronic conjunctivitis
to eradicate it
what other conditions is viral conjunctivitis commonly associated with
cold and flu
what is the most common form of conjunctivitis
viral
what are the characteristics of viral conjunctivitis
- acute
- unilateral but bilateral after 1 week
- often also get pre-auricular nodes
- self limiting - recovery after a few days only
- usually no sequelae
which virus is viral conjunctivitis caused by
adenovirus
what are the 2 variations of viral conjunctivitis
- pharyngoconjunctival fever
- epidemic keratoconjunctivitis
which adenovirus serotypes is pharyngoconjunctival fever variation of viral conjunctivitis caused by and what is this type characterised by
3, 4 and 7
characterised by pre auricular lymph node enlargement in 90% of cases
which is the commonest type of viral conjunctivitis
pharyngoconjunctival fever
after how long does the pharyngoconjunctival fever variation of viral conjunctivitis resolved
within 2 weeks
which form of viral conjunctivitis is more severe
epidemic keratoconjunctivitis
how long does epidemic keratoconjunctivitis type of viral conjunctivitis last
1-3 weeks
what 2 things is associated with epidemic keratoconjunctivitis type of viral conjunctivitis
- subconjunctival haemorrhage in 33% of cases
- may get corneal involvement - sub epithelial infiltrates in 20-30% of cases
which adenoviral serotypes is epidemic keratoconjunctivitis type of viral conjunctivitis caused by
8, 11 & 19
and produces a mixed papillary and follicular conjunctival response
what type of virus is the aden virus
a DNA virus
with 49 serotypes
which 2 ways is the adenovirus spread
- fomites (virus can survive in inanimate objects)
- contact with secretions e.g. following cough or sneeze
what are the 2 forms of chlamydial conjunctivitis
- trachoma
- follicular conjunctivitis
what 2 things is trachoma due to
- poor sanitation
- multiple untreated infections which is endemic in developing countries due to over crowding
what can trachoma cause
- palpebral conjunctival scarring
- entropion
- in some cases ectropion
- ulceration and corneal scarring (due to result of corneal exposure)
what is the treatment os trachoma associated with chlamydial conjunctivitis
antibiotics:
- tetracyclines
and
- erythromycin
what causes acute inclusion conjunctivitis form of chlamydial conjunctivitis
- chronic follicular conjunctivitis
- usually sexually transmitted
what is the presentation of chlamydial conjunctivitis
- unilateral red eye
- usually mild/diffuse
- may involve the cornea, producing punctate keratitis (& lesions similar to viral conjunctivitis)
what are the characteristics of the pathogen chlamydiae
- obligate intracellular parasite
- depend on host cell
- inert infectious particles
- culture not routine (but can be cultured by conjunctival scrape)
which 3 ways can you diagnose the pathogen chlamydia
- serology
- histology (inclusions)
- PCR
how is a conjunctival scrape carried out for detecting chlamydia
- using a kamura spatula
- sample taken from upper and lower conjunctival sac
- sample is then placed on a slide and under a microscope to identify the characteristic inclusion bodies
what are the varieties of culture media
- chocolate (aerobic and anaerobic)
- blood agar
- Mc conkey agar (coliforms)
- sabouranaud dextrose (fungi)
which agar is used for particular gram -ve organisms e.g. E coli
Mc conkey agar (coliforms)
how is antibiotic sensitivity tested
- by impregnating antibiotics onto paper discs
- placed on an agar plate
- bacteria are not able to grow around anti-biotics to which they’re sensitive
- by measuring their zones of inhibition around the discs will identify the most relevant antibiotic treatment for a infection
list the 4 types of keratitis and what micro organism causes each one
- bacterial - pseudomonas
- viral - herpes simplex
- fungal - fusiform
- protozoal - acanthamoeba
what is contact lenses the biggest risk for
bacterial and acanthamoeba keratitis
what are the 4 classifications of uveitis
- anterior
- intermediate
- posterior
- panuveitis
what are the aetiologies of uveitis
- infectious
- non-infectious
what is infected in uveitis
any part of the uveal tract e.g. iris, ciliary body or choroid, either individually or collectively
what are the 2 infectious aetiologies of anterior uveitis
- herpes simplex virus HSV (most common cause)
- varicella zoster virus VZV
what are the 4 infectious aetiologies of posterior uveitis
- toxoplasmosis (parasite)
- toxocara
- syphilis
- cyclomagalovirus CMV
which type of posterior uveitis does cyclomagalovirus CMV cause and which patients is this seen in
choroiditis and associated retinitis
seen in immunosuppressed individuals e.g. AIDS
what are the characteristics of endophthalmitis
- usually bacterial and acute
- in most cases due to exogenous bacteria that the internal structures is exposed to (due to surgery or trauma)
what are the 4 classifications of endophthalmitis
- acute post cataract
- chronic pseudophakic
- bleb-related
- post traumatic
from where in the eye can infected samples of edophthalmitis be taken from
- aqueous humour
- vitreous humour
what does the college of optometrist provide
its infection control guidance
what 6 principles of infection control does the college of optometrists provide
- principles of cleaning sterilisation and infection
- hand hygiene
- situations of greater risk
- contact lenses and ophthalmic devices such as tonometer heads
- contamination via contact lens solutions and medicine bottles
- safe disposal waste
