Encephalitis is main
presentation.
Sporadic outbreak
reported from Africa, Middle East, western Asia, North America, Caribbean
countries, and
The strain from
Transmission
Vector- over 40
Mosquitoes species can transmit the virus to human. Culex mosquitoes are the
main vectors.
The virus can infect
mosquitoes, birds, horses and humans.
Person to person
transmission can occur through
Blood
transfusion (RBC, Plasma, Platelets)
Organ
transplant
Breast
milk
Vertical
transmission
Accidental
inoculation of infected body fluid
Incubation
period is between 2-15
days.
Most are asymptomatic
(80%).
One in 5 patients has
febrile illness- fever, headache, nausea and vomiting.
Characterized by Maculopapular rashes that
spread mainly in the face and trunk.
Generalized
lymphadenopathy is common.
One in 150 patients
has neurological problems with high fever and in these
groups of patients a mortality rate as high as 10% has been
reported.
In several outbreaks,
encephalitis has been associated with high fatality particularly in the
elderly.
In addition patients
can also present with
ü
Meningitis,
ü
Acute
flaccid paralysis which is common in young patients, it mainly affects the
anterior horn cells without involvement of sensory nerve cells. There may not be
functional improvement after recovery.
ü
Rarely-
hepatitis, Pancreatitis, myocarditis, optic neuritis
Congenital
infection
·
Bilateral
chorioretinitis
·
Severe
cerebral abnormality
Investigations
Laboratory
investigations
CBC-Leukocytosis or
mild leucopenia
CSF
pleocytosis-lymphocytosis, high protein and normal glucose
CT
scan- no pathology.
MRI-
in 30 % of patients with encephalitis show white matter loss and leptomeningeal
enhancement.
Tests
The appropriate
specimens include clotted blood, Blood in EDTA, and CSF.
Serological tests- 90
% of patients with Meningoencephalitis have IgM in Serum or
CSF.
The IgM may persist
for more than 9 months
Serology is not
specific as WNV share certain antigen with other Flaviviruses like St
Louis encephalitis, Yellow fever or Dengue Fever. Ask for history of Yellow
fever or Japanese encephalitis Vaccine to avoid error in interpreting
serological test results.
PCR can be done on
blood and CSF. As viraemia is brief, PCR test may give a false negative result.
The recommendation is to do PCR testing close to the onset of illness..
Treatment
Mainly supportive-
intubations and mechanical ventilation for patient with muscle
weakness.
Ribavirin has been
tried.
Intravenous
immunoglobulin may be effective as prophylaxis or therapeutic as immunoglobulin
has been shown to neutralize infection in animal models.
Yellow fever vaccine
does not prevent infection with WNV but may prevent severe infections or
fatality.
NB: Case fatality rate
in hospitalized patients is 5-10 %.
Prevention
Insect
repellent.
Mosquitoes control measures- larvicides and insecticide spray.