WEST NILE VIRUS SURVEILLANCE PROTOCOL
2003 Season Guidance
(Note: This guidance may evolve during the
season. Please make sure you have the most current recommendations.)
- Educate the public about West Nile virus, especially regarding
elimination of mosquito breeding sites and use of personal protective
measures.
- Educate the public to report dead bird sightings to the local health
department.
- Educate physicians and hospital infection control practitioners to:
- Recognize clinical syndromes that warrant arbovirus testing (i.e.
febrile headache, aseptic meningitis, or encephalitis during late
summer and early fall), and
- Order appropriate testing for West Nile virus (WNV), La Crosse
encephalitis (LAC), Eastern equine encephalitis (EEE), and St. Louis
encephalitis (SLE).
This action should be accomplished by generating a physician alert
from the county health department and/or by asking infection control
practitioners to assist in alerting physicians.
- Educate veterinarians to consider West Nile virus as a possible
etiology of summertime encephalitis in horses.
- Educate government officials at all levels regarding mosquito
surveillance and integrated pest management as a means of preventing
cases of WNV.
- Report total dead bird sightings (crow and non-crow) and zip code
location to the West
Virginia Infectious Disease Epidemiology Program (IDEP) on a weekly
basis May 1 to November 30, 2003.
- Report recently dead (< 24 hours) birds to IDEP
immediately for possible testing for West Nile virus.
- Investigate cases of human WNV and perform a visit to the homes of
all confirmed WNV cases to visualize the outdoor environment, educate
the family about removal of containers, mosquito habitat abatement,
and use of personal protective measures, including use of mosquito
repellent. Obtain latitude and longitude of the home of the case, and
interview the case (or parents) to obtain information on the location
of other potential exposures, including time spent out of doors during
the incubation period. Include a travel history during the incubation
period. Include a travel history during the incubation period. Document using the Arbovirus Supplemental Investigation Form.
Attach the supplemental form and all appropriate laboratory
studies to the yellow card and send to the West Virginia Infectious
Disease Epidemiology Program.
- Report confirmed/probable/suspected human, equine, or avian WNV
cases urgently to IDEP.
- Given existing resources; if bird, human, or equine cases of
WNV are identified:
- increase public education to encourage use of personal protective
measures,
- increase public education to encourage elimination of mosquito
breeding sites,
- increase education of government officials at all levels regarding
mosquito surveillance and integrated pest management as a means of
preventing additional cases,
- generate an alert to physicians to intensify surveillance for
human cases, and
- generate an alert to veterinarians to intensify surveillance for
equine cases.
- If additional resources become available:
- establish local or regional mosquito surveillance and control
capacity, and
- begin viral surveillance of mosquito populations.
- Reduce disease risk through public education to
encourage:
- use of personal protective measures, and
- elimination of mosquito breeding sites.
- If additional resources become available:
reduce disease risk through development of local or regional mosquito
surveillance and control capacity.
- If a bird or
equine case is identified: prevent the development of human cases
through education of the public to use personal protective measures
and eradicate mosquito breeding sites.
- If a human case
is identified: prevent the development of additional human cases
through education of the public to use personal protective measures
and eradicate mosquito breeding sites.
- If positive mosquito pools are identified: prevent the
development of human cases through appropriate mosquito surveillance
and control.
- If additional resources become available:
prevent human cases through development of local or regional mosquito surveillance and
control capacity.
- Determine where West Nile virus is present in West
Virginia and the extent of spread (to be accomplished through dead
bird testing).
- Estimate the intensity of West Nile virus
activity, if present (to be accomplished through dead bird testing and
dead bird reports).
- Detect human and equine cases of West Nile virus,
if present.
- Determine where West Nile virus is present in
West Virginia and the extent of spread (to be accomplished through
adult mosquito surveillance using both CDC gravid and CDC miniature
light traps).
For the fourth year in a row, WNV has continued to
expand its territory, spreading over much of the United States. Many
counties in West Virginia had birds test positive in 2002. Three West
Virginia counties also had WNV- positive horses, and three positive human
cases were reported from two counties.
(See www.wvdhhr.org/bph/oehp/sdc/westnile_2002_data.htm
for up-to-date Dead Bird Reports by county in West Virginia)
Public health officials must be vigilant for WNV during mosquito season
because: 1) the mosquito vectors which carry WNV have been found in West
Virginia, and 2) WNV-positive birds, horses and humans have been identified
in West Virginia. The purpose of surveillance is to identify whether human
cases are likely so that appropriate prevention measures can be taken.
Public health has a major role in prevention and control of this disease
through surveillance, public and provider education, and through promotion
of mosquito control activities.
For reasons stated above, surveillance is an extremely important function
of public health. This season, the public health community is funded to
perform dead bird, mosquito and human surveillance. Equine surveillance will
also be possible through collaboration with the USDA and the West Virginia
Department of Agriculture. Here are the types of surveillance that should be
performed and the purpose of each type of surveillance:
- Dead Bird Surveillance: The purpose of dead
bird surveillance is to establish whether West Nile virus is present
within the jurisdiction under surveillance. This is accomplished by
testing freshly dead birds for WNV. By tracking the number of dead bird
reports, the intensity of viral activity can also be estimated (i.e.
more dead bird reports suggests more viral activity and a higher
likelihood of human cases). This information should be used to inform
the public about the level of risk within the jurisdiction so they can
take action to protect themselves.
- Mosquito Surveillance: One purpose of
mosquito surveillance is to identify mosquito breeding sites and
prioritize sites for abatement. For example, sites breeding the
treehole mosquito should be abated or larvacided if they are in close
proximity to human populations because the treehole mosquito is the
vector for La Crosse encephalitis; whereas sites breeding nuisance
mosquitoes are low priority for abatement. Another purpose of mosquito
surveillance is to determine if disease-carrying adult mosquitoes are
present. Again, this information should be used for mosquito control
so that human cases of arboviral infection can be prevented. The West
Virginia Department of Health and Human Resources is conducting
limited adult and larval mosquito surveillance at this time.
- Equine Surveillance: The full role of
equine surveillance is yet to be determined; however, horses do serve
as an important indicator of WNV activity in the jurisdiction.
Information on equine cases should be used to prevent human cases.
- Human Surveillance:
The purpose of human surveillance is to detect human WNV infection
within the jurisdiction. This information should be used to prevent
additional cases.
The ecology and public health aspects of WNV are
complex. West Virginia public health officials are encouraged to take the
necessary time to educate themselves about this disease.
According to several recent studies most WNV
infections are mild or unapparent, approximately 80% of infections are
asymptomatic. About 20% of those infected develop mild febrile illness of
sudden onset (West Nile fever) which is often accompanied by: malaise,
anorexia, nausea, vomiting, eye pain, headache, myalgia, rash and
lymphadenopathy. Symptoms are normally self-limiting and last 3 to 6 days.
Less than 1% of infections result in severe neurological disease.
Neurological presentations include: Meningitis, Encephalitis,
Meningoencephalitis and Acute flaccid paralysis. Signs and symptoms may
include fever, weakness, GI symptoms, change in mental status, ataxia,
extrapyramidal signs, cranial nerve abnormalities, myelitis, optic neuritis,
polyradiculitis and seizures. A small minority of patients may develop a
maculopapular or morbilliform rash involving the neck, trunk, arms or legs.
Encephalitis is more commonly reported than meningitis. The most significant
risk factor for developing severe neurological disease is advanced age. The
case fatality rate is estimated at 10% of those with severe neurological
symptoms (this equates to < 0.1% of total infections).
Preliminary data from clinical investigations conducted during the 2002
Arbovirus season are elucidating an expanding spectrum of neurological
disease. Emerging and evolving clinical syndromes include: Movement
disorders, Parkinsonism, Rhabdomyolysis (disintegration of muscle fibers
with excretion of myoglobin in the urine) and Acute flaccid paralysis.
Movement disorders included onset of tremors and or myoclonus (usually
facial involvement) > 5 days following initial symptoms. Parkinsonian-like
signs were seen in both encephalitis and meningitis cases, signs included:
cogwheel rigidity, bradykinesia and postural instability. Tremors were not
observed at rest. Rhabdomyolysis (other causes, such as trauma and drug
induced being ruled out) was identified in 14 WNV cases during 2002. Further
study to assess the association are needed. The syndrom of acute flaccid
paralysis usually includes asymmetric weakness without pain or sensory loss,
and elevation of CSF protein and WBC. Continued surveillance and public
health investigation is needed to fully define the scope of neurologic
illnesses associated with WNV infection.
In the temperate zone of the world, WNV encephalitis cases occur
primarily in the late summer or early fall. In the southern climates where
temperatures are milder, WNV can be transmitted year round.
West Nile virus is a member of the family Flaviviridae
(genus Flavivirus). Other members of this family include the
Hepatitis C, dengue fever, and yellow fever viruses. Serologically, it is
a member of the Japanese encephalitis virus complex that includes St.
Louis encephalitis (SLE), Japanese encephalitis, Kunjin, Murray Valley
encephalitis viruses, as well as others. It was first isolated in the West
Nile province of Uganda in 1937. Members of the family Flaviviridae are
single-stranded RNA viruses, approximately 40-60 nm in size.
Wild birds are the primary reservoir hosts; however,
the American Crow, Blue Jay, and other corvids and raptors (hawks, owls,
and eagles) are particularly susceptible. Horses, humans, and other
animals are usually considered to be dead-end or incidental hosts, since
they are not known to develop infectious-level viremia.
The principal route of West Nile virus infection in
horses, humans, and birds is through the bite of an infected mosquito.
Non-infected mosquitoes can become infected through biting and obtaining a
blood meal from infected birds. WNV is amplified during periods of adult
mosquito blood-feeding by continuous transmission between mosquito vectors
and bird reservoir hosts. Infectious mosquitoes carry virus particles in
their salivary glands and infect susceptible bird species during blood-meal
feeding. A sufficient number of vectors must feed on an infectious host to
ensure that some survive the extrinsic incubation period to feed again on a
susceptible reservoir host. Even if the mosquito is infected, less than 1%
of people bitten who become infected will get severely ill.
Multiple species of mosquitoes have tested positive for WNV, including: Aedes
(4 species), Anopheles (6 species), Coquillettidia (1
species), Culex (8 species), Culiseta (2 species), Deinocerites
(1 species), Ochlerotatus (9 species), Orthopodomyia (1
species), Psorophora (3 species), and Uranotaenia (1 species).
Of particular concern are some species of Aedes, Culex, and
Ochlerotatus that may be more inclined to bite humans. Several
species in these genera are also known cavity breeders and will breed in
artificial containers.
Five additional routes of infection have become apparent during the 2002
West Nile season. It is important to note that these other methods of
transmission represent a very small proportion of cases. New modes of
transmission are via: Transplantation, Transfusion, Breastfeeding,
Transplacental and Occupational exposures (mostly laboratory workers). (More
information may be found on the CDC’s website at: http://www.cdc.gov/ncidod/dvbid/westnile/clinical_guidance.htm)
There is no documented evidence of direct person-to-person or
animal-to-person transmission. There is concern that a person may get
WNV from handling live or dead infected birds, so people should avoid
bare-handed contact when handling dead animals, and use gloves or double
plastic bags to place carcasses in garbage cans.
The incubation period is usually three to 15 days.
There is no direct person-to-person transmission.
See section on Modes of Transmission above.
Any case of human or equine disease is defined as an
outbreak during 2003. The Infectious Disease Epidemiology Program should be
notified immediately upon any positive case finding in a human with WNV
infection, and should also be notified of suspected infection prior to
completion of testing.
WNV is confirmed in a county based on a dead bird testing positive for
West Nile virus, a positive equine case, a positive human case or by
demonstrating WNV infection in adult mosquitoes.
Encephalitis or Meningitis, Arboviral
Clinical Description
Arboviral infections may be asymptomatic or may result in illnesses of
variable severity sometimes associated with central nervous system (CNS)
involvement. When the CNS is affected, clinical syndromes ranging from
febrile headache to aseptic meningitis to encephalitis may occur, and
these are usually indistinguishable from similar syndromes caused by other
viruses. Arboviral meningitis is characterized by fever, headache, stiff
neck, and pleocytosis (> 5 white blood cells in CSF). Arboviral
encephalitis is characterized by fever, headache, and altered mental
status ranging from confusion to coma with or without additional signs of
brain dysfunction (e.g. paresis or paralysis, cranial nerve palsies,
sensory deficits, abnormal reflexes, generalized convulsions, and abnormal
movements).
Laboratory Criteria for Diagnosis
- Fourfold or greater change in virus-specific serum antibody titer,
or
- Isolation of virus from or demonstration of specific viral antigen
or genomic sequences in tissue, blood, cerebrospinal fluid (CSF), or
other body fluid, or
- Virus-specific immunoglobulin M (IgM) antibodies demonstrated in CSF
by antibody-capture enzyme immunoassay (EIA), or
- Virus-specific IgM antibodies demonstrated in serum by
antibody-capture EIA and confirmed by demonstration of virus-specific
serum immunoglobulin G (IgG) antibodies in the same or a later
specimen by another serologic assay (e.g. neutralization or
hemagglutination inhibition).
Case Classification
Probable: an encephalitis or meningitis case occurring during a
period when arboviral transmission is likely, and with the following
supportive serology:
- a single or stable (less than or equal to twofold change) but
elevated titer of virus-specific serum antibodies; or
- serum IgM antibodies detected by antibody-capture EIA but with no
available results of a confirmatory test for virus-specific serum
IgG antibodies in the same or a later specimen.
Confirmed: an encephalitis or meningitis case that is laboratory
confirmed.
Comment
Because closely related arboviruses exhibit serologic
cross-reactivity, positive results of serologic tests using antigens from a
single arbovirus can be misleading. In some circumstances (e.g. in areas where
two or more closely related arboviruses occur, or in imported arboviral disease
cases), it may be epidemiologically important to attempt to pinpoint the
infecting virus by conducting cross-neutralization tests using an appropriate
battery of closely related viruses. This is essential, for example, in
determining that antibodies detected against St. Louis encephalitis virus are
not the result of an infection with West Nile (or dengue) virus, or vice versa,
in areas where both of these viruses occur.
The seasonality of arboviral transmission is variable and depends on the
geographic location of exposure, the specific cycles of viral transmission, and
local climatic conditions. Reporting should be etiology-specific (see below; the
six encephalitides/meningitides printed in bold are nationally reportable to
CDC):
St. Louis encephalitis/meningitis
West Nile encephalitis/meningitis
Powassan encephalitis/meningitis
Eastern equine encephalitis/meningitis
Western equine encephalitis/meningitis
California serogroup viral encephalitis/meningitis (includes
infections with the following viruses: La Crosse, Jamestown Canyon, snowshoe
hare, trivittatus, Keystone, and California encephalitis viruses)
Other viral CNS infections transmitted by mosquitoes, ticks, or midges
(e.g. Cache Valley encephalitis/meningitis and Venezuelan equine
encephalitis/meningitis)
Human Serological Testing
It is impossible to clinically distinguish one type of
encephalitis from another. Any individual in West Virginia who presents with
encephalitis/meningitis during mosquito season (May 1 through November 30 in
most areas of the state) should be tested for La Crosse encephalitis (LAC),
eastern equine encephalitis (EEE), St. Louis encephalitis (SLE), and West Nile
virus (WNV).
Serum or CSF should be sent to the West Virginia Office of Laboratory
Services (OLS), 167 11th Ave, South Charleston, WV 25303 for testing
or confirmation. Sherry Nestor (304-558-3530) should be contacted to arrange
testing. Specimens should be accompanied by a completed Arbovirus Test
Submission Form when sent to the OLS.
Detection of IgM using the antibody-capture enzyme-linked immunosorbent assay
(MAC-ELISA) is optimal, and the preferred diagnostic method. Ninety-nine percent
of serum and CSF specimens tested at CDC from 1999 - 2002 had detectable IgM
antibody to West Nile virus in serum or CSF by the time of symptom onset.
Detection of IgM antibody to West Nile virus in serum or CSF collected within
eight (8) days of symptom onset is the most efficient diagnostic method.
Patients who are negative for IgM antibodies in CSF or serum specimens drawn
eight (8) to 21 days after illness onset are considered negative. Patients with
specimens drawn within 7 days of onset of symptoms that are found negative by
MAC-ELISA should have a convalescent specimen drawn at least two weeks later.
Due to the fact that IgM antibodies may persist for greater than one year,
residents in endemic areas may have persistent IgM antibodies from a previous
infection that is unrelated to their current illness. Since West Nile virus was
present in our state last year acute (drawn within 7 days of symptom onset) and
convalescent (drawn at least 2 weeks after acute specimen) serum specimen
collection and submission are recommended to confirm acute infection.
When interpreting serologic tests, it must be kept in mind that close
antigenic relationships of the flaviviruses may cause false positive results for
WNV. Persons recently vaccinated with yellow fever or Japanese encephalitis, or
recently infected with related flaviviruses (i.e. St. Louis, dengue) are likely
to test positive for WNV. The plaque reduction neutralization test (PRNT) can
then be used to distinguish between false-positives and serologic
cross-reactivity, although some degree of ambiguity may still occur.
A four-fold increase in West Nile virus-specific neutralizing antibody titer
in acute and convalescent serologies confirms acute illness.
Single serum specimens positive for WNV IgM by MAC-ELISA require confirmation
by demonstration of IgG antibodies using another serologic assay (e.g.
neutralization or hemagglutination inhibition). Specimens found to be positive
for IgM by MAC-ELISA at OLS will be followed-up with confirmatory PRNT testing.
Dead Bird Testing
Effective July 2002, dead
birds must be submitted to the Southeastern Cooperative Wildlife Disease
Study (SCWDS) at the University of Georgia School of Veterinary Medicine
for West Nile virus testing.
The dead bird submission procedure is as follows:
- Birds appropriate for testing include only those that
have died recently (< 24 hours old) and have no obvious signs of
trauma or decomposition (i.e. dried or missing eyes). If the carcass is soft
and mushy, has an obvious odor, has skin discoloration, feathers or skin
that rubs off easily, and has ants or flies, it is too decomposed for
testing.
- All species of birds can be submitted to SCWDS
for testing. However, testing may be limited to crows, blue jays,
and raptors (hawks, eagles, and owls) as the season progresses. If
this procedure changes, all local health departments will be notified
in writing by the Infectious Disease Epidemiology Program.
- Take a cooler containing ice into the field to
immediately chill the carcass(es). Use rubber gloves when picking up
sick or dead animals. If gloves are not available, hands can be
inserted into a plastic bag. A GIS reading should be taken, or the
exact location should be noted on a detailed county map.
- The Infectious Disease Epidemiology Program
must be contacted
at 1-800-423-1271 for testing approval. If approved, a unique
state identification number will be assigned to the dead bird. The
bird cannot be tested without a state ID number.
When a cluster of dead birds is reported, two dead birds from the
cluster may be accepted for testing. When clusters of dead birds
are reported, the local DNR official should be notified. DNR may wish
to do additional testing.
- Complete a "West Virginia Dead Bird Submission
Form for West Nile Virus" for each bird submitted for testing. New
forms can be downloaded from IDEP’s West Nile website at www.wvdhhr.org/bph/oehp/sdc/westnile.htm.
Please make sure that the correct form is being used. Some
information needed for each bird submitted includes the following:
State ID number
Identity and agency of person completing report
Date collected
Location (county/town/specific street address with ZIP code) including a
GIS reading
Place the paperwork and a return address label in an envelope and tape to
the outside of the shipping container. If more than one bird is submitted,
include information on each bird attached to the bagged bird.
- Birds should be double-bagged in two sealed bags prior
to packing.
- Birds must be refrigerated and shipped Monday
through Thursday. If the birds are collected on Friday, Saturday, or
Sunday, they must be refrigerated (do not freeze) and shipped
on Monday. Carcasses should be shipped via an overnight courier
(either FedEx or USPS [United States Postal Service]) in the
insulated shipping containers which were provided by the Infectious
Disease Epidemiology Program. A return address label must be
included with the container in order for it to be returned.
- The shipping container should be lined with a large plastic bag.
Individually double-bagged birds should be packed into the container
with enough blue ice packs (do not use "wet" ice) to
keep the carcasses cold. Newspaper should be stuffed in spaces
between the sides of the container and the outer plastic bag to keep
the ice packs in contact with the birds, provide insulation, and
absorb any liquid that might leak from the bags. Tape the box shut
with strapping tape.
- Send via overnight delivery to:
Dr. David Stallknecht
Southeastern Cooperative Wildlife Disease Study
College of Veterinary Medicine
The University of Georgia
Athens, GA 30602
DIAGNOSTIC SPECIMENS - WILDLIFE
Note that in addition to the SCWDS address, the words DIAGNOSTIC
SPECIMENS - WILDLIFE must appear on the label. This label covers federal
shipping regulations. Fines may be levied if specimens are shipped and are
not labeled appropriately.
- Notify the local DNR official with the name of an individual citizen (or
local health official) submitting a bird for testing as soon as possible
after the bird is reported or received. Possession of songbirds is
regulated by the federal government. Timely notification to DNR will keep
the lines of communication open and prevent misunderstanding, as well as
coordinate additional testing.
There is currently no vaccine against human WNV, and no
treatment.
Share these prevention messages with the public:
- Empty standing water in old tires, cemetery urns, buckets, plastic covers,
toys, or any other container where mosquitoes may breed
- Empty and change the water in bird baths, fountains, wading pools, rain
barrels, and potted plant trays at least once a week if not more often.
- Drain or fill temporary pools with dirt.
- Keep swimming pools treated and circulating, and rain gutters unclogged.
- Use mosquito repellents containing DEET. Apply sparingly to children
before they play out of doors, and rinse children off with soap and water
when they come back in. Do not apply repellent to the face and hands of
young children because they may rub it in their eyes. Follow label
directions and precautions closely.
- Use head nets, long sleeves, and long pants if you venture into areas with
high mosquito populations.
- Make sure window and door screens are "bug tight."
- Number of dead birds (crow and non-crow) submitted per
county for testing for WNV.
- Proportion of weeks May to November that counties submit dead bird
reports to the Infectious Disease Epidemiology Program.
- Proportion of humans with a diagnosis of encephalitis that are tested
for EEE, SLE, LAC, and WNV May to November.
- Proportion of cases with complete clinical investigation: Patient
demographics, involvement in outdoor activities, travel history and
clinical symptoms (Part 1. of Arbovirus Investigation Form completed).
- Proportion of cases with home visit completed for environmental
evaluation, including GIS coordinates of location, patient and family
education (Part 2. of Arbovirus Investigation Form completed).
- Proportion of cases investigations that are totally complete: complete
WV BPH Confidential Reportable Disease Case report (yellow card), complete
Arbovirus Investigation form and copies of supporting laboratory results
i.e. confirmatory WNV serologic or antigen results and CSF test results.
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