WEST NILE

Question 1

Organism Type

Answer 1

single-stranded RNA virus of the family Flaviviridae

Question 2

Scientific name

Answer 2

west nile virus

Question 3

Subtypes

Answer 3

None

Question 4

Common Name(s)

Answer 4

None

Question 5

Leading cause of domestically acquired arboviral disease

in the U.S

Answer 5

west nile virus

Question 6

Predisposing Factors

Answer 6

outdoor activities during spring & summer;

mosquito bites

Question 7

Transmitted Via

Answer 7

Culex mosquito; blood transfusion/organ donation;

mother to child

Question 8

Vector

Answer 8

Yes

Question 9

Incubation Period

Answer 9

2 - 6 days, but can range from 2 - 4 days

Question 10

Vaccine

Answer 10

No

Question 11

Reportable

Answer 11

Yes

Question 12

Lethal

Answer 12

Non-neuroinvasive (no); neuroinvasive (yes)

Question 13

Outbreaks tend to occur between

Answer 13

mid-July and early September

Question 14

Elevated temperatures & rainfall correlate with increased or decreased WNV
transmission & infection

Answer 14

increased

Question 15

P2P transmission is usually related to

Answer 15

blood transfusion and organ

transplantation.

Question 16

Mosquitoes become infected when they feed on

Answer 16

infected birds; then

spread virus to humans & other animals during bloodmeals.

Question 17

Horses & humans are considered

Answer 17

‘dead-end’ hosts.

Question 18

WNV should be considered in any _________ during the summer months
in WNV endemic areas.

Answer 18

febrile patient or acute neurologic

illness with recent exposure to mosquitoes

Question 19

Symptoms

Answer 19

(a) An acute systemic febrile illness that may be accompanied
by:
1) Headache, weakness, myalgia, or arthralgia
2) Gastrointestinal symptoms
3) Transient maculopapular rash

Question 20

Clinically indistinguishable from viral meningitis due to other
etiologies & typically presents with fever, headache, and
nuchal rigidity.

Answer 20

WNV Meningitis

Question 21

A more severe clinical syndrome that usually manifests with
fever and altered mental status, seizures, focal neurologic
deficits, or movement disorders such as tremor or
Parkinsonism

Answer 21

WNV Encephalitis

Question 22

(a) Typically clinically & pathologically identical to poliovirusassociated poliomyelitis and may progress to respiratory
paralysis requiring mechanical ventilation.
(b) WNV poliomyelitis often presents as isolated limb paresis or
paralysis and can occur without fever or apparent viral
prodrome.

Answer 22

WNV Acute Flaccid Paralysis

Question 23

Lab Diagnosis

Answer 23

(1) Diagnosis via identifying IgM in serum or CSF
(2) ELISA is used to detect IgM antibody
(3) Other labs to consider:
(a) If CNS symptoms are present lumbar puncture with CSF
analysis
(b) CBC is not a reliable indicator of disease

Question 24

Lab Diagnosis

Answer 24

(a) Mumps, HSV, poliovirus, measles, and pertussis.

b) Other flavivirus infections (YF, Zika, Dengue

Question 25

Treatment

Answer 25

(1) There is no specific treatment for WNV disease, and no antiviral
treatment is available.
(2) Vigorous supportive measures are the first line management protocol:
(a) Patients with severe meningeal symptoms often require pain
control for headaches, antiemetic therapy and rehydration for
associated nausea & vomiting.
(b) Patients with encephalitis require close monitoring for the
development of elevated intracranial pressure and seizures.
(c) Patients with encephalitis or poliomyelitis should be
monitored for inability to protect their airway.
(d) Acute neuromuscular respiratory failure may develop rapidly
and prolonged ventilatory support may be required.

Question 26

Disposition

Answer 26

MEDEVAC is warranted if there are signs of encephalitis, meningitis,
or paralysis.

Question 27

Prevention

Answer 27

(1) No WNV vaccines are licensed for use in humans.
(2) In the absence of a vaccine, prevention of WNV disease depends on:
(a) Community-level mosquito control programs to reduce vector
densities
(b) Personal protective measures to decrease exposure to infected
mosquitoes
(c) Screening of blood and organ donors.
(3) Personal protective measures include use of mosquito repellents,
wearing long-sleeved shirts and long pants, and limiting outdoor
exposure from dusk to dawn.
(4) Using air conditioning, installing window and door screens, and
reducing peridomestic mosquito breeding sites, can further decrease
the risk for WNV exposure.

Question 28

Disposition

Answer 28

i. WNV - Disposition
(1) Non-neuroinvasive WNV:
(a) Most patients with non-neuroinvasive WNV disease recover
completely; however, fatigue, malaise, and weakness can
linger for weeks or months.
(2) Neuroinvasive WNV:
(a) Patients who recover from WNV encephalitis or
poliomyelitis often have residual neurologic deficits.
(b) Among patients with neuroinvasive disease, the overall casefatality ratio is approximately 10%
1) Case-fatality rate is significantly higher for patients
with WNV encephalitis & poliomyelitis than WNV
meningitis.