Ch 11: Viral Infections of the Nervous System

What does the Central Nervous System include?

The brain and spinal cord

Why are Central Nervous System infections so serious?

Because the brain and spinal cord control almost everything your body does

What are two major infections of the CNS?

Meningitis and Encephalitis

What is meningitis?

Inflammation or infection of the meninges, the protective membranes around the brain and spinal cord

What is encephalitis?

Inflammation or infection of the brain tissue itself

What pathogens usually cause meningitis?

Bacteria and viruses

What pathogens usually cause encephalitis?

Viruses

What two symptoms do both meningitis and encephalitis have in common?

Severe Headache and Fever

If a person has nuchal rigidity, then they most likely have…?

Meningitis

If a person has photophobia, then they most likely have…?

Meningitis

If a person has phonophobia, then they most likely have…?

Meningitis

If a person has altered mental status then they most likely have…?

Encephalitis

If a person if having seizures, then they most likely have…?

Encephalitis

What is nuchal rigidity?

Stiff neck- pain or resistance when trying to bend the neck

What is photophobia?

Sensitivity to light

What is phonophobia?

Sensitivity to sound

What is altered mental status?

Inflammation of the brain tissue that disrupts how neurons communicate. 

What specific signs might a patient with altered mental status show?

Confusion, disorientation, personality or behavior changes, drowsiness and decreased responsiveness

What two physical exam signs are used to diagnose meningitis?

Kernig’s sign and Brudzinski’s sign

Do Kernig’s and Brudzinski’s signs work for encephalitis?

No- they only indicate meningitis

What do you do during a Kernig’s sign to test for meningitis? What sign indicates that the person is positive?

A patient lies flat and you lift their leg (90º) to try and straighten the knee; If they experience pain or resistance in the hamstring

What do you do during a Brudzinski’s sign to test for meningitis? What sign indicates that the person is positive?

You lift a patient’s head (chin to chest);  If their knees automatically bend

If either Kernig’s or Brudzinski’s sign is positive, what should you suspect?

Meningitis

How reliable are Kernig’s and Brudzinski’s signs?

They have high predictability for meningitis and low false-positive rates

What can happen if meningitis is left untreated?

It can progress to brain damage, seizures, or death

What is meningoencephalitis?

A condition where a person has both meningitis and encephalitis at the same time

What kind of symptoms does a patient with meningoencephalitis have?

A mix of both meningitis and encephalitis symptoms

Which are more common, bacterial CNS infections or viral CNS infections?

Viral CNS infections

Which are more dangerous, bacterial CNS infections or viral CNS infections?

Bacterial CNS infections

Why are bacterial CNS infections so serious?

They can progress rapidly and be deadly within hours if untreated

Are the bacteria that cause meningitis the same for all ages?

No, they are age-dependent

How do viral CNS infections compare to bacterial ones in severity?

They are usually milder, less deadly, and more manageable

What does it mean when a virus is “self-limiting”?

The body can fight it off without severe or long-term damage

Why don’t antibiotics work for viral CNS infections?

Because antibiotics only target bacteria, not viruses

What is the most common cause of viral meningitis and encephalitis in the U.S.?

Enteroviruses

Where do non-polio enteroviruses live?

In the intestines

Non-polio enteroviruses are usually mild, but can especially cause viral meningitis in…

Children

Coxsackie virus is a type of non-polio enterovirus. What disease can it cause?

Hands, foot, and mouth disease

Which herpes virus can cause encephalitis?

Herpes Simplex Virus type 1 (HSV-1)

Which herpes virus can cause meningitis, especially after a genital infection?

Herpes Simplex Virus type 2 (HSV-2)

What is another virus that can directly infect the brain and what can it cause?

Human immunodeficiency virus (HIV); HIV encephalitis

What procedure is used to diagnose meningitis or encephalitis?

a lumbar punch (spinal tap)

What is a lumbar puncture (spinal tap) used for?

Collecting cerebrospinal fluid (CSF) to diagnose meningitis or encephalitis

What is cerebrospinal fluid (CSF)?

The fluid that surrounds your brain and spinal cord

Why is CSF collected during a lumbar puncture?

To determine if the infection is bacterial or viral

During the Cerebrospinal fluid analysis, what do doctors look for?

White blood cells

What does the presence of neutrophils in CSF indicate?

A bacterial infection

What does the presence of lymphocytes in CSF indicate?

A viral infection

What does an elevated white blood cell count in CSF show?

That the immune system is fighting an infection in the brain or meninges

How many WBCs per microliter suggest a bacterial infection?

More than 1,000 cells

How many WBCs per microliter suggest a viral infection?

Less than 1,000 cells

What happens to CSF glucose in bacterial meningitis?

It decreases because bacteria use it as fuel

What happens to CSF protein in bacterial meningitis?

It increases due to inflammation

What happens to CSF glucose in viral meningitis?

It usually remains normal

What happens to CSF protein in viral meningitis?

It may be slightly increased

Which white blood cell type dominates in bacterial meningitis?

Neutrophils

Which white blood cell type dominates in viral meningitis?

Lymphocytes

A patient’s CSF shows 3,200 white blood cells per microliter.

What WBC is likely the most present and what type of infection may the patient have?

Neutrophils- Bacterial infection

A patient’s CSF shows 150 white blood cells per microliter.

What WBC is likely the most present and what type of infection may the patient have?

Lymphocytes- Viral infection

A lumbar puncture reveals WBC = 900 cells/µL. Is this value more consistent with bacterial or viral infection?

Viral Infection

What are PCR’s used for?

Detecting Infections

How are PCR’s used when diagnosing meningitis or encephalitis?

It tests the cerebral spinal fluid

What does PCR do to DNA?

Copies and amplifies DNA so small amounts can be detected

Why is PCR so useful for detecting infections?

It can find a tiny amount of pathogen DNA and make millions of copies for easy detection

What makes PCR highly specific?

Primers that target only the DNA of the pathogen being tested

What are primers in PCR?

Short DNA sequences designed to match a specific pathogen’s DNA

What is the DNA template in PCR?

The sample containing the DNA to be tested

What enzyme builds new DNA strands in PCR?

DNA polymerase

What are dNTPs in PCR?

The DNA “letters” — nucleotides 

What specific letters make up DNA nucleotides?

A, T, G, C

How many nucleotides are in the human genome?

About 3.2 billion

What type of virus causes rabies?

Rhabdoviruses

Is rabies a DNA or RNA virus?

RNA virus

How is rabies transmitted?

Animal vector- Through the bite or saliva of an infected animal

What animals most commonly carry rabies?

Dogs, bats, raccoons, skunks, and foxes

What is the incubation period for rabies?

1 to 52 weeks, depending on where the bite occurred

Why does incubation time vary in rabies? 

Because the virus travels through nerves, not the blood

What makes symptoms show up faster when a person has rabies?

The closer the bite is to the brain, the faster symptoms show up

If a person gets bit on the face or neck, will the symptoms of rabies show up faster or slower?

Faster

If a person gets bit on the foot or leg, will the symptoms of rabies show up faster or slower?

Slower

What happens if symptoms of rabies appear?

The infection is 100% fatal — no one survives once symptoms start

What treatment is available for rabies exposure BEFORE symptoms appear?

Post-exposure prophylaxis

Is there a cure for rabies?

No- once symptoms appear, there is no cure

What will happen once you get symptoms of rabies?

You will die

When should you get treatment after being exposed ro rabies?

Immediately

What does rabies post-exposure prophylaxis treatment include?

Cleaning the wound immediately, 4 doses of the rabies vaccine, and rabies IgG antibodies 

When must rabies treatment begin for survival to be possible?

Before symptoms start

What is a key symptom of rabies that affects behavior?

Hydrophobia (fear of water)

How is HSV-1 transmitted?

By direct contact

What is the incubation period of HSV-1?

About 1 week

What type of virus is West Nile Virus (WNV)?

An RNA virus

How is West Nile Virus transmitted?

Through an arthropod vector (insect) — specifically mosquito bites

What animals start the West Nile Virus cycle/where does the virus multiply?

Birds

How is the west nile virus transmitted from birds to finally, humans?

A mosquito bites an infected bird, then later bites a human

How long is the incubation period for West Nile Virus?

About 1 week

Do most people infected with WNV get sick?

No — most infections are asymptomatic

Who is most likely to develop severe WNV disease?

Older adults or people with weakened immune systems

Can West Nile Virus affect the brain?

Yes, but rarely — it can cross into the CNS in severe cases

Is there a cure for West Nile Virus?

No cure, but it’s usually not as deadly as rabies

What is the normal glucose value for CSF?

45-80 mg/dL