CNS Infections Flashcards
Meningitis
An infection which causes inflammation of the membranes covering the brain and spinal chord
Names for viral versus bacterial meningitis
Viral: aseptic meningitis (usually resolve without treatment)
Bacterial: purulent meningitis (very serious, may result in death or brain damage)
Bacterial Meningitis
Potentially life threatening disease
Fever, headache, meningismis and altered mental status in more that 85% of people
Affects all age groups but some are at higher risk
Pneumococcal meningitis most common type
Haemophilus type meningitis
Incidence declined since 1985 due to the introduction of the Haemophilus influenza b vaccine
Meningismis
Stiff neck
Photophobia
Causes of meningitis
Bacterial infections Viral infections Fungal infections Inflammatory diseases Cancer Trauma to head or spine
Viral meningitis
Generally benign, rarely fatal
Enterovirus is 80% of cases, others can be mumps or EBV
Rare but very serious: HSV
No specific treatment except for HSV/VZV - requires systemic antivirals (acyclovir)
Most clear in 3-8 days
Some common bacterial meningitis agents
S. pneumoniae N. meningitidis H. influenzae type B Listeria monocytogenes (very young and very old) Group B strep (neonates) Others
Bacterial meningitis agents for those:
Less than 3 months old (4)
Group B strep
Listeria monocytogenes
E. coli
Strep pneumoniae
Bacterial meningitis agents for those:
3 months to 18 years (3)
N. meningitidis
S. pneumoniae
H. influenzae (rare)
Bacterial meningitis agents for those:
18 to 50 (3)
S. pneumoniae
N. meningitidis
H. influenzae
Bacterial meningitis agents for those: Over 50 (3)
S. pneumoniae
L. monocytogenes
Gram negative bacilli
Lumbar puncture
Collects cerebral spinal fluid to check for the presence of disease or injury
Spinal needle is inserted, usually between the 3rd and 4th lumbar vertebrae in the lower spine
Permits the urgent distinction of bacterial meningitis from viral and examination of the CSF allows precise diagnosis
Typical findings in meningitis: bacterial versus viral
- Cell types
- CSF protein level
- CSF glucose level
- B: presence of NEUTROPHILS, V: presence of LYMPHOCYTES
- B: 10X normal, V: 2-3X normal
- B: very low, V: normal
Why is there not that much glucose present in bacterial meningitis CSF?
Because there is so much inflammation that you impair sugar transport
NOT that they use it up
Neisseria meningitidis
Gram negative
Aerobic diplococcus
Polysaccharide capsule
13 serogroups classified by their capsule (5 disease ones: A, B, C, Y, W-135)
Often appear intracellular on gram stain
Catalase and oxidase +
Will grow on both chocolate and bloodagars
Meningitis common clinical presentations
Fever and headache (flu like symptoms) Stiff neck Nausea Altered mental status Seizures Up to 40% fatality even with appropriate treatment
Meningococcemia common clinical presentations
Rash
Vascular damage
DIC (disseminated intravascular coagulation)
Multi-organ failure
Shock
Death can occur <24 hours
Fatality rate 3-10% even with appropriate treatment
Meningitis transmission
Humans only
Asymptomatic pharyngeal carriage can occur in 10-30% of the population
Transmission by saliva, most often by aerosol effect (coughing, sneezing), kissing, etc
Over crowding fosters transmission
Incubation period varies between 2-10 days
If you see N. meningitis in the lab, should you tell the doctor to treat right away?
No! Because 30% of people have it at all times anyways
3 vaccines for N. meningitidis
Monovalent serogroup C
Quadrivalent serogroups A, C, Y, W-135
Monovalent serogroup B
Listeria monocytogenes
Gram positive bacilli Catalase positive Tumbling motility at 25degC Umbrella motility in semi-soft agar Beta hemolytic CAMP test +
Clinical manifestations of Listeria
Meningitis
Abortion (premature delivery of stillborn or acutely ill infant)
Perinatal septicemia (infant often dies within a few minutes of hours, symptoms reflect disturbances of respiratory, circulatory or central nervous system, if infant survives, meningitis common, often fatal or leads to permanent mental deficiency)
Other influenza like illness
What do you use to treat bacterial meningitis?
Vanco and a high dose of a 3rd generation cephalosporin
If they are elderly, add ampicillin
Listeriolysin O
Most significant virulence factor
Responsible for beta hemolysis of erythrocytes and destruction of phagocytic cells
Aids in escape from the phagosome
Present in all strains of L. monocytogenes
Should you do the lumbar puncture before or after giving antibiotics?
Before
Unless there is going to be a delay and you need to get treated asap
If you give antibiotics first you might sterilize the CSF :(
Mental status changes
Seizures, decreased consciousness, confusion
Ex: encephalitis has meningitis symptoms + mental status changes
When to think viral CNS infection
CSF exam and clinical presentation
CSF exam: Gram stain negative, lots of lymphocytes, occasionally increased RBCs, high protein, normal glucose
Clinical presentation: usually acute onset, can effect healthy hosts but more likely immunocompromised, frequently occurs as meningoencephalitis
Enterovirus
(family, enveloped?, nucleic acid, disease it causes, who is at risk, outbreaks?, clinical symptoms, treatment/vaccine?, diagnosis)
Family: picronaviridae
Non-enveloped, + ssRNA
Respiratory virus
Causes 30-50% of viral meningitis (aseptic meningitis)
People at risk: healthy, neonates, immunocompromised
Seasonal outbreaks
Clinically: usually resp symptoms with severe headaches, can last a while but no long term consequences
No treatment or vaccine
Diagnosis: clinical suspicion/epidemiology, CSF profile, PCR
Treatment: pain control, hydration
Herpes simplex virus
family, nucleic acid, types and diseases, outbreaks?, mortality, pathogenesis, diagnosis, treatment
Family: Herpesviridae
Enveloped dsDNA
HSV-1 (oral) and 2 (genital) but both can cause CNS disease
Most common cause of sporadic viral encephalitis in NA
No seasonal outbreaks
High mortality even with treatment
Pathogenesis: rarely from primary exposure, usually from reactivation (latency in sensory ganglion)
Symptoms: fever, headache, focal symptoms (temporal lobe), seizures/mental status change frequent), long term consequences possible, immundeficiency can lead to fatal dissemination)
Diagnosis: clinical suspicion, MRI, CSF profile, PCR
Treatment: antivirals (acyclovir), no vaccine
Acyclovir
Can be used to treat herpes
Nucleotide analogue
Gets incorporated and stops DNA elongation process
Its a prologue though and needs to be activated
Arboviruses
Arthropod-borne viruses
Major vectors: mosquitoes and ticks
Primary symptoms: mostly asymptomatic or non-specific, fever/headache/seizure, usually meningoencephalitis
Incidence and severity varies with virus and host
Long term consequences possible
Seasonal and geographic distribution
Depends on presence of vector and reservoir
Diagnosis: clinical suspicion, CSF protein, PCR, serology
Supportive treatment
Some vaccines (JEV and YFV)
Vector controll efforts and insect repellant stuff
Vector
Typically a biting insect or tick that transmits a disease or parasite from one animal to another
4 Arboviruses that cause encephalitis
- West Nile virus
- Japanese encephalitis virus
- Eastern equine encephalitis virus
- La Cross virus
Reservoir
An organism or population that directly or indirectly transmits a pathogen while being virtually immune to its effects
Epidemic (or urban) cycle
Reservoir is humans - high level of viremia
Mosquitoes transfer between humans
Ex: dengue, yellow fever, chikungunya, etc
Enzootic cycle (sylvatic or jungle cycle)
Reservoir: vertebrate - harbors a virus with no ill effects
Mosquitoes transfer between animals (like primates) and humans are accidental hosts
No person-to-person spread
Viremia not sufficient in humans to be picked up by the insect vectors
Epizootic cycle (rural cycle)
Reservoir: wild birds
Virus transmitted between domestic animals and insect vectors
Epidemic outbreaks in the animal
Amplifying host - possible spillover into humans
Ex: JEV, St-Louis, an Western encephalitis virus
How does Eastern Encephalitis Virus get into humans?
Indirect spillover into humans through a bridge vector
This is an arthropod that acquires virus from an infected wild animal and subsequently transmits the agent to human or secondary host
Rabies virus encephalitis
(family, nucleic acid, enveloped?, where globally, transmission, symptoms, diagnosis, treatment, prevention
Family: Rhabdoviridae
Large enveloped virus, ssRNA (-)
More common in underdeveloped countries
Universally fatal once you get symptoms
Transmitted through saliva of infected animals (raccoons, bats, foxes, etc)
Infected animals show no fear for humans, act very agitated, scared of water
Neurotropic (affinity for nerve cells/tissue) - ascending
Long incubation period (3 weeks)
Symptoms: fever, agitation, hydrophobia, painful spasms followed by excessive saliva, universally fatal without treatment
Diag: clinical suspicion, PCR and DFA, serology
Treatment: rabies Ig post exposure
Prevention: vaccination
Meningitis vs encephalitis
Meningitis = inflammation of meninges (coverings of brain and spinal chord) Encephalitis = inflammation of brain itself
