Central Nervouss System Infections 2.pdf

Central Nervouss System Infections

1. CentralNervousSystem Infections

2. MicrobialinvasionoftheCNSisuncommon,duetothepresenceof
the blood–brain and blood–CSF barriers, which limit the spread of
infection.
Onceinfectiousagentshavecrossedthese barriers,theygenerally
cause neurological disease by involving the meninges (meningitis) or
the brainsubstance(encephalitis).
Viralaetiology ofmeningitisismostcommon,followedbybacterial
meningitis,withcerebralabscesses&viral encephalitisasrarities.
The spinal cord (in myelitis) or peripheral nerves (in neuritis) are
occasionallyaffected.
CentralNervousSystem Infections

4. RoutesofInfection
Theorganismsmaygainaccesstothe CNS byseveral routes.
Hematogenousspread:This isthemostcommon route,whereentryinto
thesubarachnoidspaceisgainedthroughthechoroidplexusorthrough
otherbloodvessels ofthe brain
Directspread from aninfectedsitepresent closetomeninges: otitismedia,
mastoiditis,sinusitis,etc.
AnatomicaldefectinCNS:Itmayoccurasaresultofsurgery, trauma,
congenitaldefectswhichcanalloworganisms forready&easyaccessto
CNS
Directintraneural spreadalongthenerve:This istheleastcommon
route, occurs in cases of rabies virus or herpes simplex virus (HSV)
infection.

5. Gram positive
Streptococcus pneumoniae
Streptococcus agalactiae(Group B)*
Listeriamonocytogenes*
Gram negative
Neisseriameningitidis
Haemophilus influenzaetype b
Escherichia coli*
Pseudomonas aeruginosa*
Proteus species *
*Mainly isolated from neonates
Also Mycobacterium tuberculosis and Treponemapallidum
5
Possible pathogens

6. VIRUSES
Particularly coxsackieviruses, echovirus, and arboviruses. Also,
herpes simplex 2 virus, varicellazoster virus, and lymphocytic
choriomeningitisvirus (LCM).
FUNGI
Cryptococcus neoformans(mainly in AIDS patients) and less
commonly Aspergillusspecies
PARASITES
Trypanosomaspecies and Naegleriafowleri
6
Possible pathogens
Commensals
Cerebrospinal fluid has no normal microbial flora.

7. Specimencollection
Specimen collection is only for diagnosis or for the treatment of
disease.
Ventricularpuncturetoobtain CSFcanbeperformedbyaphysicianin
specialcircumstances.
Typically,sterilelumbarpuncturebetweenL2 andL3vertebraeor
betweenthe L3andL4vertebraeisthemost commoncollectionarea.
Alltestingon CSFspecimensshouldbeperformedimmediatelyupon
receiptofspecimenbecauseofrapidcellulardegeneration

11. RoutineCSFanalysis
RoutineCSFanalysistypicallyincludesaphysical,chemical&
microscopicanalysis.
1.Grossexamination
A.NormalCSF:isclear &colorless.
B.AbnormalCSF:Turbidityismostoften producedbytheincreased
presenceofWBCsorbymicroorganisms.
C.Leukocytescount normally0-5lymphocytes

12. 2.Chemical examination
A.Totalprotein inCSF
Normally,CSFproteinranges between15and45 mg/dl
B.CSFglucose isinequilibriumwithplasma glucose.
Normal values in the CSF range from 50 to 80 mg/dL or
approximately60%ofplasmaglucoselevels.

13. 3.Microbiologicalexamination
Gramstain
Culturemedia
Biochemicaltest
Serology

14. Differentiation between different
microbiologicalagents(CSF)

15. Thank you