WEST NILE Flashcards
Organism Type
single-stranded RNA virus of the family Flaviviridae
Scientific name
west nile virus
Subtypes
None
Common Name(s)
None
Leading cause of domestically acquired arboviral disease
in the U.S
west nile virus
Predisposing Factors
outdoor activities during spring & summer;
mosquito bites
Transmitted Via
Culex mosquito; blood transfusion/organ donation;
mother to child
Vector
Yes
Incubation Period
2 - 6 days, but can range from 2 - 4 days
Vaccine
No
Reportable
Yes
Lethal
Non-neuroinvasive (no); neuroinvasive (yes)
Outbreaks tend to occur between
mid-July and early September
Elevated temperatures & rainfall correlate with increased or decreased WNV
transmission & infection
increased
P2P transmission is usually related to
blood transfusion and organ
transplantation.
Mosquitoes become infected when they feed on
infected birds; then
spread virus to humans & other animals during bloodmeals.
Horses & humans are considered
‘dead-end’ hosts.
WNV should be considered in any _________ during the summer months
in WNV endemic areas.
febrile patient or acute neurologic
illness with recent exposure to mosquitoes
Symptoms
(a) An acute systemic febrile illness that may be accompanied
by:
1) Headache, weakness, myalgia, or arthralgia
2) Gastrointestinal symptoms
3) Transient maculopapular rash
Clinically indistinguishable from viral meningitis due to other
etiologies & typically presents with fever, headache, and
nuchal rigidity.
WNV Meningitis
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
WNV Encephalitis
(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.
WNV Acute Flaccid Paralysis
Lab Diagnosis
(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
Lab Diagnosis
(a) Mumps, HSV, poliovirus, measles, and pertussis.
b) Other flavivirus infections (YF, Zika, Dengue
Treatment
(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.
Disposition
MEDEVAC is warranted if there are signs of encephalitis, meningitis,
or paralysis.
Prevention
(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.
Disposition
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.
