CNS infections

Question 1

What is the most common method of entry of bacteria into the CNS?

Answer 1

Bloodborne invasion

Question 2

What is encephalomyelitis?

Answer 2

Inflammation of spinal cord

Question 3

What is meningoencephalitis?

Answer 3

Inflammation of the brain and meninges

Question 4

What makes the junctions of the blood brain barrier vs blood-CSF barrier?

Answer 4

BBB - tightly joined endothelial cells surrounded by glial processes (i.e. astrocytes)
BCB - endothelial cells with fenestrations and tightly joined choroid plexus epithelium

Question 5

What are the three ways in which microbes can cross the BCB or BBB?

Answer 5

1. Infecting cells which comprise the barrier
2. Being passively transported across in intracellular vacuoles
3. Being carried across by WBCs

Question 6

How do LPS and Techoic Acid increase the chances that the microbe will get into the CSF?

Answer 6

Cause inflammation. Cytokine release can cause an edema which allows immune cells to flow out of the bloodstream and into the CSF

Question 7

What causes the CSF to become visibly turbid?

Answer 7

Increases in PMNs and proteins

Question 8

What are examples of normal microbes / normal flora inhabiting mucosal surfaces which are the common cause of meningitis?

Answer 8

Strept pneumoniae -> found in Upper Respiratory Tract
N. meningitidis - found in URT and pharynx
H. influenzae - found in URT
Group B strept - found in GI tract
E. coli K1 - Found in GI tract and UG tract

Question 9

What happens to protein, glucose, and WBC’s in CSF during bacterial meningitis?

Answer 9

Protein goes up
Glucose goes down (bacteria eat it)
WBC goes up (>50% are PMNs)

Question 10

What happens to protein, glucose, and WBC’s in CSF during aseptic meningitis?

Answer 10

Aseptic = viral
Protein goes up only slightly
Glucose remains the same
WBC goes up (not as much as bacterial)
Less than half of WBC will be PMNs, except early on in disease course

Question 11

What patient population normally has WBC and protein in the CSF?

Answer 11

Normal neonates have small amounts

Question 12

What are the two forms of acute bacterial meningitis?

Answer 12

1. Meningeal bacterial infection

2. Infections causing inflammation of meninges without infection in CSF

Question 13

What are the symptoms of acute bacterial meningitis? What is indicative of a very severe infection?

Answer 13

Sudden: high fever, severe / persistent headache, “nuchal rigidity”, nausea, and vomiting

Severe: confusion, sleepiness, and difficulty waking up

Question 14

What is the primary cause of bacterial meningitis in the US?

Answer 14

Streptococcus pneumoniae

Question 15

How is S. pneumoniae spread, and what is its morphology / lab identification?

Answer 15

Aerosols or direct contact with oral secretions

Gram positive diplococci - optochin sensitive, and swells during Quellung reaction

Question 16

What are the major virulence factors of S. pneumoniae?

Answer 16

Capsule
Pneumolysin - a cytotoxin released when bacteria lyses, inhibits antibody binding to bacteria
Techoic Acid

Question 17

What are the risk factors for meningitis caused by S. pneumoniae?

Answer 17

immunosuppression (i.e. HIV or recent influenza), distant foci of infection (i.e. chronic otitis media), or low levels of circulating antibodies to capsule

Question 18

Which H. influenza serotype is responsible for most cases of meningitis? Where does it live?

Answer 18

Hib = Serotype B, with polyribitol phosphate

Asymptomatic carrier in many people’s nasopharynx, but can be spread by aerosol or oral secretions

Question 19

What is the morphology of H. influenzae and how is it identified?

Answer 19

Gram negative coccobacillus

Identified by needs for factor V (NAD) and factor X (hemin), thus needs to be grown on chocolate agar

Question 20

What are the meningococcus capsule serotypes causing disease and which one is the most common?

Answer 20

A
C
B
Y
W135

like TCBY but ACBY

B causes 50%, and it has sialic acid in it so we couldn’t make a vaccine for it until recently

Question 21

What are the virulence factors other than capsule for meningococcus and what is its species name?

Answer 21

Pili - for adhesion to epithielum
LOS - lipooligosaccharide, like LPS, same genus as gonorrhea which uses LOS

Neisseria meningitidis

Question 22

What puts you at risk for Neisseria meningitidis?

Answer 22

Close contact with infected people and areas of outbreak, i.e. college dorms or army barracks

It is the second leading cause of bacterial meningitis

Question 23

Other than regular meningitis symptoms, what is distinctive about the symptoms of meningococcal meningitis?

Answer 23

Hemorrhagic rash with petechiae, due to the septicemic inflammation from LOS

Petechiae are from disseminated intravascular coagulation (septic shock)

Question 24

What is the morphology of N. meningitidis and how can it be told apart from gonorrhea?

Answer 24

Gram negative diplococci
Grows fastidiously on Chocolate Agar
Oxidase positive

Told apart by:
Via sugar fermentation MeninGococcal = ferments maltose and glucose

Question 25

What puts you at higher risk for meningitis as a college student?

Answer 25

Lifestyle changes, including poor eating habits, alcohol use, smoking, and pulmonary infections

->change immune function and microbiota composition

Question 26

For a polymicrobial brain abscess, what is the major distinguishing feature between that and meningitis?

Answer 26

Polymicrobial abscesses will cause behavioral changes and lead to hemiparesis or speech difficulties, and typically will have no involved nuchal rigidity

Question 27

What is the appearance of a polymicrobial abscess on CT and why?

Answer 27

A ring-enhancing appearance around the lesion when contrast is used, because the abscess is surrounded by a fibrous capsule within 4-5 days

Question 28

What are the risk factors for polymicrobial abscesses and what is the most common agent?

Answer 28

Immunocompromised, or distal infection like sinusitis or otitis media

Common agents are Streptococcus species along with anaerobes.

Question 29

What frequently causes brain abscesses in AIDS patients?

Answer 29

Cryptococcus and Toxoplasma

Question 30

What is the primary virulence factor of Cryptococcus neoformans?

Answer 30

Capsule, protecting against macrophage uptake and complement deposition

Question 31

What is the natural reservoir of Cryptococcus and how does one get a brain abscess with them?

Answer 31

Pigeon excretions or rotting wood

Usually get a primary lung infection via inhalation, and infection remains latent because disseminating through body in immunosuppression

Question 32

What is used in the lab to detect Cryptococcus?

Answer 32

India ink can detect the yeast form

Question 33

What are the risk factors for Coccidioides outbreaks? What is its primary virulence factor?

Answer 33

Dust storms, earthquakes, and earth excavations where arthroconidia are favored for dispersion, leading to lung inhalation

Primary virulence factor is spherule particle too large for macrophage engulfment

Question 34

What does Trypanosoma cruzi cause and what carries it?

Answer 34

Chagas disease - carried by Triatomine bug

Question 35

What are the acute symptoms of Chagas disease?

Answer 35

Romana’s sign - pathopneumonic - eyelid swelling. Accompanied by fever and acute encephalitis

Question 36

What are the chronic symptoms of Chagas disease?

Answer 36

Affects heart, colon, or CNS

Question 37

who do i lov most

Answer 37

da memo