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Infectious Diseases > CNS Infections > Flashcards

CNS Infections Flashcards

1
Q

What does CNS stand for?

A

Central Nervous System

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2
Q

What is the CNS comprised of?

A

The brain and spinal cord

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3
Q

What 3 layers protect the CNS?

A
  • Hard (bone)
  • Soft (Meninges)
  • Liquid (Cerebro-spinal fluid)
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4
Q

How does the bone protect the CNS?

A

It protects from mechanical pressure and deformation. It is also a barrier against infection.

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5
Q

What are the meninges?

A

o Membranes covering the brain and spinal cord.

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6
Q

What are the 3 membranes of the meninges?

A

 Pia Mater – innermost layer
 Arachnoid – middle layer
 Dura mater – outermost (toughest) layer

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7
Q

What is cerebro-spinal fluid and where is it found?

A

o Clear, colourless, odourless fluid found in the brain and spinal chord.
o Found in the subarachnoid space between the pia mater and the arachnoid.

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8
Q

How many ml of cerebro-spinal fluid can a personal have at any one time?

A

125-150ml

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9
Q

How many ml of cerebro-spinal fluid is produced every 24 hours?

A

600ml

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10
Q

What is cerebro-spinal fluid derived from?

A

Blood plasma.

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11
Q

Name the functions of the cerebro-spinal fluid

A 
o	Buoyancy
o	Protection
o	Prevention of brain ischaemia
o	Homeostasis
o	Clearing waste
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12
Q

Name the barriers which protect the CNS.

A

Blood-brain barrier

Blood-CSF barrier

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13
Q

Name the routes of invasion to infect the CNS.

A
  • Blood-borne infections (most common)
    o Microorganisms enter the blood and travels to the blood-brain barrier
  • Via peripheral nerves
  • Local invasion from infected ears or sinuses, local injury or congenital defects
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14
Q

What is the most common infection caused when the blood-brain barrier is crossed by microorganisms.

A

Encephalitis

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15
Q

What is the most common infection caused when the blood-CSF barrier is crossed by microorganisms.

A

Meningitis

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16
Q

How do microorganisms transverse barrers?

A
  • Growing across the barrier by infecting the cells that form the barrier
  • Being passively transported across the barrier in intracellular vacuoles
  • Being carried across by infected white cells
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17
Q

What barrier does Poliovirus overcome to infect the CNS?

A

The blood-brain barrier

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18
Q

How is Poliovirus transmitted?

A

Faecal-oral route

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19
Q

Describe how the Poliovirus enters the body and causes infection around the body.

A
  • The poliovirus is ingested and infects the gut (the Gut Associated Lymphoid Tissue).
  • It then travels to the Lymph and the blood and begins to infect other organs (e.g. Spleen and Liver).
  • This causes a generalised infection mostly associated with the blood.
  • Symptoms of fever etc occur.
  • In some cases, the virus can cross the blood-brain barrier or blood-CSF barrier. If it crosses the blood-CSF barrier, Meningitis can be caused. If it crosses the blood-brain barrier, Encephalitis and often paralysis are likely.
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20
Q

Explain how invasion of microorganisms occurs through peripheral nerves using the examples of Herpes Simplex and Varicella-zoster.

A

o Both infect the skin initially.
o The infections are not fully removed by the immune system and become dormant in ganglions in the peripheral nervous system.
o They then can reoccur by travelling up the axons using retrograde transport.

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21
Q

What is the reoccurrence of Varicella-zoster usually called?

A

Shingles

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22
Q

How do invasions of the peripheral nerves travel up axons?

A

By retrograde transport

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23
Q

How does the body respond to invasion of the CNS by viruses?

A
  • Increase in lymphocytes in the CSP
  • Slight increase in protein
  • CSF remains clear
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24
Q

How does the body respond to invasion of the CNS by bacteria?

A
  • Increase in polymorpho-nuclear leukocytes
  • Increase in proteins
  • CSF goes cloudy
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25
Q

Outline some of the consequences of CNS infections.

A
  • Can be life threatening
  • Inflammation and edema
    o Caused by infection in the CNS
  • “Closed box”
    o Means that the inflammation and edema become critical.
  • Can take weeks to recover
  • Some damage is permanent
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26
Q

Why do CNS infections only damage the host?

A

It is a closed system.

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27
Q

What is Encephalitis?

A

Inflammation of the brain resulting in brain damage.

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28
Q

Name some of the causes of Encephalitis.

A
  • Infection
    o Mostly by viruses (most common is Herpes Simplex – causes severe sporadic acute focal encephalitis).
  • Immune attack – auto-immune or post-infection
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29
Q

What are the symptoms of Encephalitis.

A
  • Starts of with mild flu-like or headache
  • Alterations of level of consciousness
    o Mild confusion or drowsiness
    o Loss of consciousness or coma
  • High temperature
  • Aversion to light
  • Seizures
  • Inability to speak
  • Sensory changes
  • Neck stiffness
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30
Q

What is the mortality rate of Encephalitis?

A

10-30%

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31
Q

Name some of the sporadic causes of Encephalitis.

A 
-	Herpes simplex
o	Infant and adult forms
-	Mumps 
o	Less common than meningitis
-	Varicella zoster
o	Associated with ophthalmic zoster
-	Rabies
o	In India 150,000 deaths per year
o	In USA <10 deaths per year
-	HIV
o	Sub-acute encephalitis often associated with other CNS infections
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32
Q

Name some of the outbreak causes of Encephalitis

A 
-	Polio and other enteroviruses
o	Uncommon because there is a vaccine and very few countries who have wild type polio present. 
o	Associated with paralysis
-	Mosquito-born Togaviruses
-	Mosquito-borne Bunyaviruses
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33
Q

Name some of the slow viral causes of Encephalitis

A
  • Rubella
    o Infection in-utero or sub-acute sclerosing panencephalitis (SSPE)
  • Measles
    o SSPE following uncomplicated measles
  • JC virus (Human polyoma virus 2)
    o Usually immunocompromised, specially AIDS
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34
Q

Name the bacteria that cause Encephalitis and how common each are as a cause.

A 
-	Treponema pallidum (syphilis)
o	Rare 
o	May affect the brain
-	Mycoplasma pneumoniae
o	Rare
o	Causes pneumonia originally
-	Borrelia burgdorferi (Lyme disease)
o	Uncommon
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35
Q

Name the protozoa and fungi that cause Encephalitis.

A 
-	Cryptococcus neoformans
o	Rare complication
-	Toxoplasma gondii
o	Meningoencephalitis
-	Plasmodium falciparum
o	Cerebral malaria
-	Trypanosoma spp.
o	Sleeping sickness in Africa
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36
Q

Name the Atypical agents of the scrapie group that cause Encephalitis.

A
  • Prions – Creutzfeldt-Jakob and kuru in humans

- Spongiform encephalopathy

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37
Q

When, how and why do some post-vaccinational / post-infectious agents cause Encephalitis?

A
  • Occurs as a rare complication 2-3 weeks after exposure to certain viruses of vaccines
  • Strong autoimmune component
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38
Q

How does Clostridium tetani affect the CNS and what symptoms does it cause?

A

Blocks inhibitory neurotransmitter. Excitatory transmitter therefore cycles. No inhibition of excitation transmitter. Continuous stimulation = muscle rigidity and lockjaw.

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39
Q

Where are Clostridium tetani commonly found and how people are generally exposed to this microorganism.

A

They are found in the soil and are present in the environment. People tend to be exposed via cuts.

40
Q

What toxin is present in clostridium tetani and how does this travel?

A

Tetanospasmin - carried in peripheral nerve axons to the CNS.

41
Q

How is infection caused by Clostridium tetani treated?

A

Anti-tetanus immunoglobulin.

Vaccine that lasts 10 years also available.

42
Q

Where is Clostridium botulinum found?

A

It is found in the soil and so contaminates fruit and vegetables. Frequently found when foods are canned or preserved without appropriate steralisation.

43
Q

How does Clostridium botulinum affect people?

A

The motor and autonomic system is affected leading to weakness and paralysis followed by respiratory muscle failure.

44
Q

What is the treatment for infections caused by Clostridium botulinum?

A

immunoglobulin and respiratory support

45
Q

What is the mechanism of action for Clostridium botulinum causing infection of the CNS?

A

Acetyl choline containing vesicles inhibited. Acetyl Choline is not released. No stimulation in the motor end plates.

46
Q

What is Meningitis?

A

Inflammation of the tissues that cover the brain and spinal cord.

47
Q

In what people are viruses most likely to cause Meningitis?

A

Children

48
Q

What are the most common viruses that cause MEningitis?

A

The most common viruses that cause Meningitis are Enterovirus, Mumps and Herpes Simplex.

49
Q

What an organism must do to cause Meningitis?

A
  • Colonise and invade mucosa
  • Survive in the blood stream
  • Cross the blood-brain/ blood-CSF barrier
  • Survive within the CSF
50
Q

Name some host defence methods against Meningitis.

A
  • Secretory IgA antibodies
  • Cellular cilia activity
  • Mucosal epithelium
  • Complement antibacterial activity
  • Cerebral endothelium
51
Q

Name some virulence factors of Pathogens to avoid host defences against Meningitis.

A
  • IgA protease secretion
  • Ciliostasis
  • Adhesive pili
  • Cell surface avoids stimulating complement
  • Rapid bacterial replication
  • Capsule to avoid phagocytosis.
  • Membrane damaging toxin
    o Pneumolysin
     Leukotoxic
     Inhibits immune cell activity
     Activates compliment and contributes to inflammation
  • IgA Protease
    o Inactivates secretory antibody
52
Q

How does Pneumolysin work as a virulence factor of pathogens to avoid host defences against meningitis ?

A

It is Leukotoxic and so inhibits immune cell activity. It also activates compliment and contributes to inflammation.

53
Q

How does IgA Protease work as a virulence factor of pathogens to avoid host defences against meningitis ?

A

Inactivaes secretory antibodies.

54
Q

What are the host defences against colonisation and mucousal invasion of harmful bacteria?

A

Secretory IgA
Cellular cilia activity
Mucosal epithelium

55
Q

What are the bacterial evasion mechanisms against Secretory IgA,
Cellular cilia activity and
Mucosal epithelium

A

IgA protease secretion
Ciliostasis
Adhesive pili

56
Q

What are the host defences against harmful bacteria surviving in the blood stream?

A

Complement antibacterial activity

57
Q

What are the bacterial evasion mechanisms against complement antibacterial activity ?

A

Cell surface avoids stimulating complement.

58
Q

What are the host defences against harmful bacteria crossing the blood-brain barrier?

A

Cerebral endothelium

59
Q

What are the bacterial evasion mechanisms against cerebral endothelium?

A

Passage through tight junctions between cells.

60
Q

What are the host defences against harmful bacteria surviving within the cerebro-spinal fluid?

A

Poor opsonic activity

61
Q

What are the bacterial evasion mechanisms against poor opsonic activity?

A

Rapid bacterial replication

62
Q

Name some risk factors for meningitis.

A 
Reduced Immunity: o	Asplenia
o	Diabetes
o	Alcohol abuse
o	HIV
o	Hypogammaglobinaemia
63
Q

What type of Meningitis does Haemophilus Influenzae cause?

A

b

64
Q

What is different in each of the 6 different types of HAemophilus Influenzarr?

A

Different capsular polysaccharides

65
Q

What issues/ infections can Haemophilus Influenzae cause?

A

Pneumonia, septic arthritis, sinusitis, otitis media, conjunctivitis, chronic bronchitis

66
Q

What type of microorganism are Haemophilus influenzae?

A

Gram -ve coccobacilli

67
Q

Are Haemophilus influenzae capsulated?

A

No

68
Q

What do Haemophilus influenzae require for growth ?

A

Blood constituents

69
Q

Where are Haemophilus Influenzae commensal?

A

The throat

70
Q

What is the virulence of Haemophilus Influenzae related to and how does this work?

A

Virulence related to a capsule – impedes phagocytosis

71
Q

Where is the reservoir for Haemophilus influenzae and how is it transmitted?

A
  • Reservoir = humans
    o Up to 80% of people are carriers
  • Transmission = droplet infection
72
Q

Are Haemophilus influenzae catalase and oxidase +ve or -ve?

A

+ve

73
Q

Describe how Haemophilus influenzae can be grown in the lab.

A
  • Will only grow on chocolate agar under 4% carbon dioxide

- X (haemin) and V (NAD) factors must be provided by discs to allow growth on nutrient agar

74
Q

Are Haemophilus influenzae latex agglutination +ve or -ve?

A

+ve

75
Q

How does Neisseria meningitidis cause death?

A

Most deaths are caused by septicaemia, not the actual meningitidis.

76
Q

What is the incubation period of Neisseria meningitidis?

A

1-3 days

77
Q

WHat type of organisms are Neisseria meningitidis?

A

Gram -ve diplococci

78
Q

Are Neisseria meningitidis oxidase +ve or -ve?

A

+ve

79
Q

How do Neisseria meningitidis grow on blood agar?

A

As pearly looking colonies

80
Q

What causes variety in Meningococcal disease?

A
  • Varies by a number of factors; serogroup, age and prompt antibiotic treatment
81
Q

Where are Streptococcus pneumoniae commensals?

A

The upper respiratory tract

82
Q

How do Streptococcus pneumoniae grow?

A

As diplococci or chains

83
Q

What issues do Streptococcus pneumoniae cause?

A
  • High incidence of infection leading to pneumonia and bacteraemia – 4% of these infected sufferers will develop Meningitis.15-20% association with sequelae.
    Also causes Septicaemia in splenectomised patients.
84
Q

what type of organisms are Listeria monocytogenes ? Also describe the conditions required for growth.

A

Motile, non-sporing, Gram +ve rod bacillus.

They are aerobic and facultatively anaerobic and grow from 1-45 degress Celsius.

85
Q

What type of haemolysis do Listeria monocytogenes cause?

A

Beta

86
Q

Who does infection by Listeria monocytogenes most commony affect?

A
  • Affects pregnant women, neonates, elderly and immunocompromised patients
87
Q

What can occur if infections caused by Listeria monocytogenes arn’t treated?

A
  • If not treated, high risk of meningitis especially in neonates
88
Q

What are the symptoms of viral meningitidis?

A

Mild, flu-like headache

89
Q

Why are the viral meningitidis reported numbers not representative?

A

Viral meningitis is under reported. Symptoms can be very mild and so numbers tend to report more severe cases.

90
Q

How does Milliary tuberculosis cause Meningitis?

A
  • Milliary tuberculosis subtype starts in the lungs and migrates through the lymphatic nodes to the brain.
91
Q

Where does Mycobacterium tuberculosis affect mostly?

A

The lungs

92
Q

How fast does Mycobacterium tuberculosis grow?

A

Slowly

93
Q

Where in the body and who does Cryptococcus neoformans mostly affect?

A
  • Primary infection of the lungs

- Found mostly in patients with depressed cell-mediated immunity

94
Q

Where are Naegleria fowlerii found and how do they infect humans, leading to Meningitis?

A

o Free living in fresh water
o If inhaled, can reach the meninges through the olfactory tract and cribriform plate
o Rapid onset and high mortality

95
Q

Who does infection by- Acanthamoebaa castellanii most frequently affect and how does it enter the body?

A

o More commonly affects those that are unwell or immunocompromised
o Thought to enter via the skin or respiratory tract

Infectious Diseases (9 decks)

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