INFECTIONS OF THE NERVOUS SYSTEM Flashcards
Neuroanatomy and neurophysiology
Brain and spinal cord are suspended in CSF and surrounded by three layers of meninges: - The ...... mater -.......... mater together called the leptom...............; - Dura mater or pachymeninges.
Infection of the brain parenchyma
- Ence………….,
Infection of meninges
- Me………….
Infection of spinal chord tissue
- My………….
However all may be affected at the same time.
Neuroanatomy and neurophysiology
Brain and spinal cord are suspended in CSF and surrounded by three layers of meninges: - The pia mater -Arachnoid mater together called the leptomeninges; - Dura mater or pachymeninges.
Infection of the brain parenchyma
- Encephalitis,
Infection of meninges
- Meningitis
Infection of spinal chord tissue
- Myelitis.
However all may be affected at the same time.
Infections of the CNS
Relatively infrequent, but have extremely serious consequences
- Untreated men……….. is fatal in 7…% of cases.
- Antibiotics have reduced this to <10%.
Childhood CNS infections can leave severe neurological impairment.
Distinctive area
- Well protected and isolated by the skull and bl. b………… ………. b…. but highly vulnerable.
Infections of the CNS
Relatively infrequent, but have extremely serious consequences
- Untreated men……….. is fatal in 7…% of cases.
- Antibiotics have reduced this to <10%.
Childhood CNS infections can leave severe neurological impairment.
Distinctive area
- Well protected and isolated by the skull and blood brain barrier but highly vulnerable.
Distinct features of CNS infection
Limited space therefore effects of infection are magnified
- Mi………. swelling and infla………… cause sig…………. damage.
Blood brain barrier
- In………. passage of micr…………. and to….. substances into the brain and CSF
- Impedes the passage of hum…….. and cel………… defence substances from the bl…….. as well as antibiotics.
Distinct features of CNS infection
Limited space therefore effects of infection are magnified
- Minor swelling and inflammation cause significant damage.
Blood brain barrier
- Inhibits passage of microorganisms and toxic substances into the brain and CSF
- Impedes the passage of humoral and cellular defence substances from the blood as well as antibiotics.
Infectious agents involved
Relatively few pathogens involved in CNS infection.
- These must have special characteristics that allow them to localise in the CNS.
Distinct categories:
- Bacterial men……….. usually caused by pne…………………… and menin…………… but do not generally infect brain pare………..
- Staphyl……………. and anaerobic strept…………. cause brain absc……….. but rarely cause men………..
Infectious agents involved
Relatively few pathogens involved in CNS infection.
- These must have special characteristics that allow them to localise in the CNS.
Distinct categories:
- Bacterial meningitis usually caused by pneumococci and meningococci but do not generally infect brain parenchyma.
- Staphylococci and anaerobic streptococci cause brain abscesses but rarely cause meningitis.
Tropism of viruses
Polio shows tropism for ……… neurons of the sp……..cord and me………….
Mumps for the epe……….. of the foetus.
Related to distribution of receptors on specific neural cells and differences in b………….. flow.
- Eg. Polio virus commonly affects an……….. h…….. cells of the spinal cord cells on the side of do………. hand
Tropism of viruses
Polio shows tropism for motor neurons of the spinal cord and medulla,
Mumps for the ependyma of the foetus.
Related to distribution of receptors on specific neural cells and differences in blood flow.
- Eg. Polio virus commonly affects anterior horn cells of the spinal cord cells on the side of dominant hand
Epidemiology of CNS infections
Age:
- Newborn meningitis most commonly caused by Group B streptococci (capsulated)
- Neuro………….. strains of E. c……… with capsule composed of ……… antigen.
Both have capsules composed of poly………… rich in si………. acid which aid bacterial adherence and growth in the m………….
- Children and young adults more often affected by meni………… infections.
- N.me…………types A,B,C W135.
- B most common in the UK
Epidemiology of CNS infections
Age:
- m Newborn meningitis most commonly caused by Group B streptococci (capsulated)
- Neuropathogenic strains of E. coli with capsule composed of K1 antigen.
Both have capsules composed of polysaccharide rich in sialic acid which aid bacterial adherence and growth in the meninges.
- Children and young adults more often affected by meningococcal infections.
- N.meningitidis types A,B,C W135.
- B most common in the UK
Epidemiology of CNS infections
- Ence……….. in infants most likely to be caused by ……….oviruses spread by fa………. oral route.
- Most common cause in adults is H….
…………viruses also common and often distinct geographical distribution
- Ja………….. encephalitis
- St. L……… encephalitis.
Epidemiology of CNS infections
- Encephalitis in infants most likely to be caused by enteroviruses spread by faecal oral route.
- Most common cause in adults is HSV.
Arboviruses also common and often distinct geographical distribution
- Japanese encephalitis
- St. Louis encephalitis.
Entry to the CNS
Most infectious agents enter via blood circulation.
- The choroid pl………, where C……. is fo………. is a common place of entry.
Highly vascular
- Inf……….. on the blood side may result in spillage of microorganisms into the CNS side.
- Correlates with micr………load in the bl………..
Neural route – rabies, HSV.
Entry to the CNS
Most infectious agents enter via blood circulation.
- The choroid plexus, where CSF is formed is a common place of entry.
Highly vascular
- Inflammation on the blood side may result in spillage of microorganisms into the CNS side.
- Correlates with microbial load in the blood.
Neural route – rabies, HSV.
Spread and Multiplication
Once in the CNS microorganisms are in a relatively hidden compartment with fewer defence mechanisms than other areas.
- Complement levels are l……., partly because of p……. penet…….. from blood
- CSF also partially inacti……… complement.
Ly……. or phag………. does not occur to the same extent in the brain, meninges and CSF.
Spread and Multiplication
Once in the CNS microorganisms are in a relatively hidden compartment with fewer defence mechanisms than other areas.
- Complement levels are low, partly because of poor penetration from blood
- CSF also partially inactivates complement.
Lysis or phagocytosis does not occur to the same extent in the brain, meninges and CSF.
Meningitis
Can be classified by:
-Clinical presentation: acu.., suba….., or chr……..;
-aetiology: bacterial, viral or fungal;
Epidemiology: sporadic or epidemic.
acute usually ba………….
- N.me……………
- Group …………. streptococci
- Strep.pneumoniae All capsulated bacteria.
- E.coli.
Subacute or chronic
- fu………. (eg. Cryptococci)
- tubercle b………….
Meningitis
Can be classified by:
-Clinical presentation: acute, subacute, or chronic;
-aetiology: bacterial, viral or fungal;
Epidemiology: sporadic or epidemic.
acute usually bacterial
- N.meningitidis
- Group B streptococci
- Strep.pneumoniae All capsulated bacteria.
- E.coli.
Subacute or chronic
- fungi (eg. Cryptococci)
- tubercle bacilli.
Meningococcal Meningitis
Meningococci are acquired by aerosol droplets from
asymptomatic carriers.
- Carriers have protective antibodies
- Up to 10% of the population have the bacteria in their throats
- Rises to 25% in 15-19 yr olds.
Gain access to dee……… areas through phary………… area.
Susceptibility to meningococci also related to con……….. def………… in the late components of the com………. cascade.
Seasonal- winter months for type B and C.
Do viral infections predi…….. to infection?
Type ….. thrives in drier cli……….
Meningococcal Meningitis
Meningococci are acquired by aerosol droplets from asymptomatic carriers.
- Carriers have protective antibodies
- Up to 10% of the population have the bacteria in their throats
- Rises to 25% in 15-19 yr olds.
Gain access to deeper areas through pharyngeal area.
Susceptibility to meningococci also related to congenital deficiency in the late components of the complement cascade.
Seasonal- winter months for type B and C.
- Do viral infections predispose to infection?
Type A thrives in drier climates
Spread, multiplication and damage
Meningococcal infection may involve meningitis or be secondary to meningococcal sep…………. which is very serious
-Involves sh………… and intra………….. coa………….. (DIC) because of high levels of bacterial end…………..
Acute meningitis characterised by:
- Fe………
- Stiff ne……..
- Head……………..
- Occasionally CNS dysfunctions.
Spread, multiplication and damage
Meningococcal infection may involve meningitis or be secondary to meningococcal septicaemia which is very serious
- Involves shock and intravascular coagulation. (DIC) because of high levels of bacterial endotoxin.
Acute meningitis characterised by:
- Fever
-Stiff neck
-Headache
- Occasionally CNS dysfunctions.
Treatment
Antibiotics must penetrate the C….. in an a………… form.
- B la……….. often used, although they are highly polar and enter the C….. poorly through B………
- Conc 15% that of serum.
- Entry enhanced because of capillary leaks as a result of ………….. and then therapeutic levels reached.
- Need to achieve 8-10 x the MBC.
Chloramphenicol
- Lypo………….. and readily crosses BBB and blood-CSF barrier, not dependent on infla………….., but may cause side effects.
Treatment
Antibiotics must penetrate the CSF in an active form.
- B lactams often used, although they are highly polar and enter the CSF poorly through BBB.
- Conc 15% that of serum.
- Entry enhanced because of capillary leaks as a result of inflammation and then therapeutic levels reached.
- Need to achieve 8-10 x the MBC.
Chloramphenicol
Lypophilic and readily crosses BBB and blood-CSF barrier, not dependent on inflammation, but may cause side effects.
Viral meningitis
Viraemia can allow viruses opportunity to involve CNS.
- As…………. me…………….
Brain usually involved so should be called meningoen…………………
Meningeal sig…….. str…………..
- St…….. ne………
- Head………………
Milder disease
- Low to moderate inf…………. and CSF contains lymp…………….
Virus can be detected in the C……….
Viral meningitis
Viraemia can allow viruses opportunity to involve CNS.
- Aseptic meningitis.
Brain usually involved so should be called meningoencephalitis.
Meningeal signs stronger
- Stiff neck
- Headache.
Milder disease
- Low to moderate inflammation and CSF contains lymphocytes.
Virus can be detected in the CSF.
Laboratory diagnosis of Meningitis:Examination of Cerebrospinal fluid
CSF is obtained by ………….
pun……….. at the base of the spin……..
Record macroscopic appearance.
Count the c………. present in a counting ch………….
In a modified Fuchs Rosenthal counting chamber
Depth 0.2mm
Counting 5 large squares gives the count in cells/mm3
Laboratory diagnosis of Meningitis:Examination of Cerebrospinal fluid
CSF is obtained by lumbar puncture at the base of the spine.
Record macroscopic appearance.
Count the cells present in a counting chamber.
In a modified Fuchs Rosenthal counting chamber
Depth 0.2mm
Counting 5 large squares gives the count in cells/mm3
