Infections in the Nervous System

Question 1

How is the brain “immune privileged?”

Answer 1

Because the brain has a physical (blood-brain) barrier as well as a lack of antigen-presenting cells, immune response is highly controlled. Inflammation is also highly controlled by a high presence of anti-inflammatories.

Question 2

What are the four common causes of neurological infections?

Answer 2

1. Viruses.
2. Bacteria.
3. Fungi.
4. Parasites.

Question 3

What is the cause of rapidly emerging infections? (5)

Answer 3

1. Susceptible populations due to war, poverty, and famine.
2. Medical practices.
3. Alterations of human and animal contact (farms, pets).
4. Rapid and frequent global movement of animals and humans.
5. Climate change and economic development.

Question 4

What is meningitis?

Answer 4

Inflammation of the meninges presents as fever, neck stiffness, cranial neuropathies (nerve damage)

Question 5

What is encephalitis?

Answer 5

Swelling of the brain (cortical tissue), presents as fever, confusion, coma, seizure.

Question 6

What is myelitis?

Answer 6

Inflammation of the spinal cord, presents as limb weakness, fever, back pain, sensory loss.

Question 7

What is an abscess?

Answer 7

Tender mass created in response to an infection, presents as fever and seizure.

Question 8

What is neuropathy?

Answer 8

Damage to nerves, presents as localized pain, fever, weakness.

Question 9

What are the two signs of meningitis?

Answer 9

1. Kernig’s sign: inability to straighten leg when hips are flexed at 90 degrees due to stiffness in hamstrings.
2. Brudzinski’s sign: Severe neck stiffness causes hips or legs to flex.

Question 10

What are the three layers of the meninges?

Answer 10

1. Dura mater
2. Arachnoid mater
3. Pia mater

Question 11

How may a patient with a neurological infection present?

Answer 11

Either with symptoms that relate to a syndrome, or they may present as acute/chronic.

Question 12

What is the next step in care after a patient presents to a clinician with acute neuro-infection?

Answer 12

Identify the exposure risks, such as:

• Exposures to be avoided.
• Actions taken to prevent further development of disease.
• Identification of co-morbidities.

Question 13

After a physical exam, what is the next step in diagnosing a patient with neurological infection?

Answer 13

The clinician must identify the localization of the infection:
- Meninges, brain, or spinal cord.

Question 14

What two forms of imaging are typically used with diagnosing neuro-infection?

Answer 14

CT or MRI scans.

Question 15

What two forms of tests can be/are taken directly after the localization of infection in the nervous system is identified?

Answer 15

Neuroimaging or Blood tests.

Question 16

After the initial sequence of tests are run, how may a diagnosis proceed?

Answer 16

Cerebrospinal fluid tests are taken via lumbar puncture.

Question 17

What is the most abundant cell in the brain?

Answer 17

Astrocytes.

Question 18

What are the functions of astrocytes?

Answer 18

Astrocytes can control the blood brain barrier, guide and support neurons through myelination, reuptake glutamate to prevent toxicity, and excrete immunity molecules.

Question 19

What are microglia?

Answer 19

Macrophage-type glial cells within the nervous system that both support young neurons as well as participate in immune response during diseased state.

Question 20

What is the normal quiescent role of microglia?

Answer 20

To act as both support molecules and ‘immune’ sensors.

Question 21

What is the activated role of microglia?

Answer 21

To both ingest foreign molecules via phagocytosis, present antigens, and respond to immunity threats via cytokine release.

Question 22

What is a retrovirus?

Answer 22

A virus in which the DNA of a cell is manipulated by a foreign invader (virus) as a result of infection.

Question 23

What is HERV? How are these viruses transmitted?

Answer 23

Human endogenous retroviruses, use RNA as genetic material and are thus able to manipulate host DNA. However, due to their endogenous nature, HERVs cannot be transmitted between individuals. They can only be transmitted through inheritance.

Question 24

How do HERVs support evolution?

Answer 24

Glycoproteins produced by some HERVs actually have a beneficial effect on human survival.

Question 25

What are opportunist infections?

Answer 25

Secondary infections that occur due to the weakening of the immune system.

Question 26

What cells are infected by HIV? Why is this important when considering the progression of the virus and possible treatment?

Answer 26

Microglia are majorly infected by HIV. Since there are copious amounts of microglia in the brain and drugs cannot infiltrate the brain as they can the body’s circulation, the brain serves as a virus reservoir where microglia can remain affected and unresponsive to ART. Therefore it is important to start ART treatment earlier before a reservoir expands in the brain.

Question 27

What is HAND?

Answer 27

HIV-associated neurocognitive disorders.

Question 28

What are some symptoms associated with HAND?

Answer 28

1. Memory loss.
2. Neuropsychiatric dysfunction.
3. Motor abnormalities.
4. Immuno-deficiency

Question 29

What occurs to neurons in the basal ganglia in result of HAND?

Answer 29

Death/pruning of pyramidal neuronal cells in the basal ganglia, causes major loss of function.

Question 30

What is HSE?

Answer 30

Herpes Simplex Virus Encephalitis.

Question 31

What treatment reduced mortality in HSE patients from 100-20%?

Answer 31

Acyclovir.

Question 32

How is HSV-1 thought to be transmitted?

Answer 32

Through inhalation via nasal passages and integration/intrusion into the brain via olfactory passages.

Question 33

How are the Zika virus and Guillain-Barre Syndrome similar?

Answer 33

Both peripheral nervous system disorder that occurs in adults.