West Nile Virus

Question 1

West Nile Virus should be considered in:

Answer 1

anyone with a febrile or acute neurologic illness who has had recent exposure to mosquitoes, blood transfusion, or organ transplantation, especially during the summer in areas where the virus is active.

Question 2

What should be in the differential for West Nile?

Answer 2

1) Common causes of encephalitis & aseptic meningitis (herpes simplex, enteroviruses)
2) Other arboviruses (La Crosse, St. Louis encephalitis, Eastern equine encephalitis, Powassan viruses)

Question 3

True or false: West Nile is a nationally notifiable condition.

Answer 3

True! Report that mess!

Question 4

Incubation period for West Nile?

Answer 4

Typically 2-6 days, but can be from 2-14 days or even several weeks in immunocompromised folks.

Question 5

What percentage of West Nile cases are subclinical or asymptomatic?

Answer 5

70-80%

Question 6

When West Nile is symptomatic, what are the symptoms?

Answer 6

Acute systemic febrile illness with:
Headache
Weakness
Myalgia or arthralgia
GI symptoms
Transient maculopapular rash

Question 7

What percentage of West Nile cases develop into neuroinvasive disease?

Answer 7

1% (that’s not many!)

Question 8

What are the symptoms of neuroinvasive West Nile?

Answer 8

Meningitis
Encephalitis
Acute flaccid paralysis

Question 9

West Nile meningitis presentation:

Answer 9

1) Clinically indistinguishable from viral meningitis due to other etiologies
2) Fever
3) Headache
4) Nuchal rigidity

Question 10

West Nile encephalitis presentation:

Answer 10

1) More clinically severe than WNV meningitis
2) Fever
3) Altered mental status
4) Seizures
5) Focal neurologic deficits
6) Movement disorders (tremors, parkinsonism)

Question 11

West Nile acute flaccid paralysis presentation:

Answer 11

1) Clinically & pathologically identical to poliovirus-associated poliomyelitis.
2) Damage to anterior horn cells
3) May progress to respiratory paralysis requiring ventilation
4) Limb paresis or paralysis
5) Can occur without fever or viral prodrome

Question 12

Routine clinical labs in West Nile:

Answer 12

Usually nonspecific

Question 13

What is the prognosis like for those with non-neuroinvasive West Nile or West Nile meningitis?

Answer 13

Complete recovery

Question 14

Which symptoms may linger for weeks or months?

Answer 14

Fatigue, malaise, & weakness

Question 15

Among patients with neuroinvasive West Nile, what is the case fatality ratio?

Answer 15

Approx 10%, but higher for those with WNV encephalitis & poliomyelitis than with WNV meningitis.

Question 16

How is lab testing for West Nile accomplished?

Answer 16

Testing of serum or CSF to detect WNV-specific IgM antibodies.

Question 17

How soon are WNV-specific IgM antibodies detectable?

Answer 17

3-8 days after onset of illness

Question 18

How long do WNV-specific IgM antibodies persist?

Answer 18

30-90 days, but longer persistence has been documented. For this reason, antibodies may represent a past infection.

Question 19

What is the treatment for West Nile disease?

Answer 19

No specific treatment. Supportive care.

Question 20

What kind of supportive care?

Answer 20

Meningeal symptoms: pain control for headaches, antiemetics & rehydration for GI symptoms
Encephalitis: Monitoring for ICP & seizures
Poliomyelitis: Monitored for inability to protect airway & may require ventilation

Question 21

What drugs have been shown to benefit those with West Nile disease?

Answer 21

None have shown specific benefit to date.

Question 22

What vaccine is effective for West Nile disease?

Answer 22

There ain’t one. Don’t let the skeeters bite you. ;)