Flashcards in Tasos CNS and Eye infections Deck (47)
What does the CNS consist of?
Brain and spinal cord
What are the meninges?
Protective membranes of CNS
Dura mater (2 layers)
- outermost membranes
- middle layer
- Inner membrance closest to brain and spinal cord
Between pia mater and arachnoid membrane in subarachnoid space filled with CSF
What are the 2 forms of meningitis?
Acute and chronic
Next questions concerned with acute meningitis
How does viral meningitis compare with bacterial?
Viral meningitis more common than bacterial but generally less serious
How is viral meningitis spread and what is its incubation period?
Spread between people by coughing or sneezing, through poor hygiene or in sewage polluted water
- Incubation period can be up to 3 weeks
What are the symptoms of viral meningitis?
Similar to bacterial form but severe meningitis will result in hospital admittance
- Diarrhea can occur with mild viral meningitis
What virus is the most common cause of viral hepititis?
- found in intestines of humans, therefore present in faeces and sewage polluted water
- Most cases occur in summer months
What are common signs and symptoms of bacterial meningitis?
- In persons over 2
> high fever
> stiff neck
Other symptoms include:
In newborns and infants
High fever, stiff neck and headaches may be hard to detect
Other signs are:
> Poor feeding
Patients of any age can have seizures
What is the cause of bacterial meningitis and what are the common infective agents?
- Serious infection of the CNS around the brain and SC and meninges
- Common agents:
> Haemophilus influenzae (Pitmans type B strain)
> Neisseria meningitidis
> Streptococcus pneumoniae
How is bacterial meningitis spread and how is it treated?
Spread from person to person by contact with discharges from nose or throat of infected individual
- Treated with antibiotics
What age of people is Haemophilus influenzae type B (Hib) meningitis found in?
- very rare after age of 4
What is the structure of Haemophilus species and where are they normally found?
Small Gram Negative Rods
Component of normal throat flora and is often associated with lower respiratory tract infections
How is Hib tested for?
Satellite phenomenon test
- Hib will only grow in presence of Haematin and NAD
- This phenomenon is known as satellitism
- Hib gets its haematin from blood agar and NAD from Staphylococcus streaked across the culture
What is Neisseria meningitidis?
- One of the most common causes of meningitis worldwide
- Intracellular gram negative coccus - often in pairs
What 2 diseases can Neisseria meningitidis cause and which is most severe?
Meningitis - inflammation of meninges
Septicaemia - blood poisoning form of the disease
Both can kill in hours
Septicaemic form most severe
Where is Neisseria meningitidis common and when do outbreaks usually occur?
- Common in sub Saharan Africa (called the meningitis belt)
- Outbreaks occur mainly when groups from different areas get together for first time and share their microbial flora i.e first week of uni
What are the symptoms of Neisseria meningitidis?
- Pinpoint red spots
- High fever
- Severe malaise (feeling very unwell)
- Nausea and vomiting
- Stiff neck
What causes red spots and rashes in Neisseria meningitidis patients?
Caused by bleeding from bloodstream pooling under the skin
- Bleeding occurs when blood vessels are damaged by the release of endotoxin in large amounts
What is another effect of blood leaking in Neisseria meningitidis?
Blood pressure falls dramatically
- reduces circulation to extremities
- In some cases gangrene will occur
What is used in prevention of Neisseria meningitidis?
Meningococcal vaccine available against four most common strains (A, C, Y, W-135)
- can be used in humans older than 2
- 85-100% effective in treating A and C
- No vaccine against type B strain
What is Naegleria fowleri and what does it cause?
- Unicellular parasite
- Ability to transform from an amoeba to a flagellate to a cyst form
- Causes primary amoebic meningoencephalitis
What is chronic meningitis?
Forms of meningitis where organisms invade the meninges and fluid surrounding the brain or there is damage to the skull and organisms leak in
- Develops over weeks (acute strikes suddenly)
- Symptoms similar to acute
How do brain abscesses cause meningitis?
- Bacteria or fungi infect brain causing inflammatory reponse
- Infected brain cells, white blood cells and microorganisms collect in limited area
- This is enclosed by membrane that forms around to create a mass
- Imflammation causes swelling, which puts pressure on delicate brain tissue, causing damage
- Mass can cause blockage of blood vessels causing hypoxia and further damage
What are the eyelids and how are they useful in pathogen protection?
- Upper and lower eyelids are folds of skin that can cover the eye
- Blink to form mechanical barrier from light, wind, dust and foreign objects (very quick reflex)
- Eyelids help to spread moisture (tears) over surface of eye
How are tears produced and why are they important?
- Tear fluid formed in the tear gland and then transported via number of ducts to eye surface
- Fluid is drained through the tear canal into the lacrimal sac, which then is connected with nose
- Tear film important for moisture and to wash away particles
- Film mostly composed of tear fluid i.e salt and water and other things
What is the main constituents of tear fluid?
Tear fluid contains:
Some of these substances fight against bacterial infection
Why is the conjunctiva susceptible to infection?
Epithelial outer surface of eye - exposued to environment
Covered by eyelids - creates a warm, moist, enclosed environment in which organism can establish infection
What is conjunctivitis?
- Referred to as pink eye
- Inflammation of the conjunctiva (membrane that covers the sclera)