West Nile virus (WNV) infection is
caused by a virus transmitted by mosquitos. Culex sp. mosquitos are known
to transmit West Nile virus which is the most common arthropod-borne virus (arbovirus)
identified in California.
Many factors influence when and
where West Nile virus outbreaks occur including
weather, number of birds that maintain the virus, number of infected mosquitoes,
and human behavior. Updates on the latest West Nile virus activity can be
found at http://www.westnile.ca.gov/.
Additional information on West Nile virus including prevention tips, mosquito
control, healthcare provider guidance, and surveillance maps, is located at
http://www.cdc.gov/westnile/index.html. For dead bird reporting, please
contact the California State West Nile Virus program at 877-WNV-BIRD
(877-968-2473).
The Los Angeles County Public Health Laboratory (PHL) performs EIA testing for
WNV on hospitalized patients or those evaluated in an emergency department
setting with aseptic meningitis, encephalitis, acute flaccid paralysis syndrome
(atypical Guillain-Barré syndrome) and outpatients with possible WNV fever.
Public Health laboratory services are also available for confirmatory testing of
West Nile virus positive results on serum specimens.
For WNV serology, parallel testing of acute and convalescent
serum specimens is preferred. Specimens should be marked clearly as "acute" and "convalescent." The optimal time for collection of acute
blood is as soon as arboviral disease is suspected and up to 7 days after
symptom onset. If the IgM is negative in the serum sample and WNV is highly
suspected, another serum sample should be collected 2-3 days after the first
serum. Convalescent serum specimens should be collected 10-30 days after symptom
onset. WNV IgM is usually present in immunocompetent individuals by day 5 of
illness onset. For immunocompromised patients, WNV antibody response may be
delayed.
Additional serological and molecular
testing for WNV on serum and CSF is available through the California Department
of Public Health - Viral and Rickettsial Diseases Laboratory (VRDL). VRDL
also performs CSF testing for other etiologies causing aseptic meningitis or
encephalitis.
Specimens wished to be sent to VRDL
should also include a State laboratory test request form in addition to a
completed Los Angeles County Public Health Laboratory test request form. Current
forms can be downloaded from the following websites:
http://www.cdph.ca.gov/programs/vrdl/Pages/CurrentVRDLSpecimenSubmittalforms.aspx
http://publichealth.lacounty.gov/lab/labforms.htm.
Completed test request form(s)
should accompany each specimen type. Each specimen must be labeled with the
patient name and a second identifier (date of birth or medical record number),
date of collection, and specimen type. Include a copy of previous test
results and any pertinent patient history with the specimen including onset
date. Send specimens by courier or overnight shipper using the appropriate
transport conditions for the specimen type. Ship packages Monday-Thursday to
avoid weekend deliveries. Frozen specimens should be shipped on dry ice.
Acceptable specimen types and
required specimen volumes are shown below. Samples should be transported on cold
packs as soon as possible following collection. If samples cannot be transported
immediately, they may be held at 4-8°C for up to 72 hours before shipping.
Otherwise, specimens should be frozen at -70°C and shipped on dry ice.
|
Test Name
|
Performing Lab
|
Specimen Type
|
Specimen Requirement
|
|
WNV EIA, IgM and IgG
|
PHL
|
Serum
|
5-7 mL collected in red top or serum separator tube
|
|
WNV EIA, IgM and IgG
|
VRDL
|
Serum
|
5-7 mL collected in red top or serum separator tube
|
|
WNV EIA, IgM only
|
VRDL
|
CSF
|
2-3 mL
|
|
WNV IFA, IgM and IgG
|
VRDL
|
Serum
|
5-7 mL collected in red top or serum separator tube
|
|
Plaque reduction neutralization
|
VRDL
|
Serum
|
5-7 mL collected in red top or serum separator tube
|
|
WNV real-time PCR
|
VRDL
|
CSF
|
2-3 mL
|
|
WNV real-time PCR
(non-diagnostic purposes only)
|
VRDL
|
Serum, acute
|
5-7 mL collected in red top or serum separator tube
|
|
Enterovirus real-time PCR
|
VRDL
|
CSF
|
2-3 mL
|
|
Herpes real-time PCR
|
VRDL
|
CSF
|
2-3 mL
|
Also refer to Acute Communicable Disease Control's letter to
physicians and laboratories (WestNileVirus.pdf).
