Penyakit Sungai Nil Barat
Penyakit West Nile
West Nile is a virus most commonly spread to people by mosquito bites.
In North America, cases of West Nile virus (WNV) occur during mosquito season,
which starts in the summer and continues through fall. WNV cases have been
reported in all of the continental United States. There are no vaccines to
prevent or medications to treat WNV. Fortunately, most people infected with WNV
do not have symptoms. About 1 in 5 people who are infected develop a fever and
other symptoms. About 1 out of 150 infected people develop a serious, sometimes
fatal, illness. You can reduce your risk of WNV by using insect repellent and
wearing long-sleeved shirts and long pants to prevent mosquito bites.
Symptoms
No symptoms in most people. Most
people (8 out of 10) infected with West Nile virus do not develop any
symptoms.
Febrile illness (fever) in some people. About
1 in 5 people who are infected develop a fever with other symptoms such as
headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people
with this type of West Nile virus disease recover completely, but fatigue and
weakness can last for weeks or months.
Serious symptoms in a few people. About
1 in 150 people who are infected develop a severe illness affecting the central
nervous system such as encephalitis (inflammation of the brain) or meningitis
(inflammation of the membranes that surround the brain and spinal cord).
·
Symptoms of severe illness include high fever, headache, neck
stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness,
vision loss, numbness and paralysis.
·
Severe illness can occur in people of any age; however, people
over 60 years of age are at greater risk. People with certain medical
conditions, such as cancer, diabetes, hypertension, kidney disease, and people
who have received organ transplants, are also at greater risk.
·
Recovery from severe illness might take several weeks or months.
Some effects to the central nervous system might be permanent.
·
About 1 out of 10 people who develop severe illness
affecting the central nervous system die.
Diagnosis
·
See your healthcare provider if you develop the symptoms described
above.
·
Your healthcare provider can order tests to look for West Nile
virus infection.
·
To learn more about testing, visit our Healthcare Providers page.
Treatment
·
No vaccine or specific antiviral treatments for West Nile virus
infection are available.
·
Over-the-counter pain relievers can be used to reduce fever and
relieve some symptoms
·
In severe cases, patients often need to be hospitalized to receive
supportive treatment, such as intravenous fluids, pain medication, and nursing
care.
·
If you think you or a family member might have West Nile virus
disease, talk with your health care provider.
Transmission
West
Nile virus is most commonly spread to people by the bite of an infected
mosquito.
Mosquitoes become infected when they feed on infected birds.
Infected mosquitoes then spread West Nile virus to people and other animals by
biting them.
In a very small number of cases, West Nile virus has been spread
through:
·
Exposure in a laboratory setting
West Nile virus is not spread:
·
Through coughing, sneezing, or touching
·
By touching live animals
·
From handling live or dead infected birds. Avoid bare-handed
contact when handling any dead animal. If you are disposing of a dead bird, use
gloves or double plastic bags to place the carcass in a garbage can.
·
Through eating infected birds or animals. Always follow
instructions for fully cooking meat from either birds or mammals.
West
Nile virus disease is a nationally notifiable condition. Cases are reported to CDC by state and local health
departments using standard case definitions. Arboviral surveillance
data are reported to CDC through ArboNET. In addition to human disease, ArboNET
maintains data on arboviral infections among presumptive viremic blood donors, veterinary
disease cases, mosquitoes, dead birds, and sentinel animals.
Arboviral surveillance data are also available at the webpages of
the following organizations:
West
Nile Virus & Dead Birds
West
Nile virus has been detected in variety of bird species. Some infected birds,
especially crows and jays, are known to get sick and die from the infection.
Reporting and testing of dead birds is one way to check for the presence of
West Nile virus in the environment. Some surveillance programs rely on citizens
to report dead bird sightings to local authorities.
How do birds get infected with West Nile virus?
West Nile virus is transmitted to birds through the bite of
infected mosquitoes. Mosquitoes become infected by biting infected birds. Some
birds that are predators (such as hawks and owls) or scavengers (such as crows)
may become infected after eating sick or dead birds that were already infected
with West Nile virus.
Do
birds infected with West Nile virus die or become ill?
Yes. Since West Nile virus was discovered in the United States in
1999, the virus has been detected in over 300 species of dead birds. Although
some infected birds, especially crows and jays, frequently die of infection,
most birds survive.
Can
I get West Nile virus directly from birds?
There is no evidence that a person can get infected from handling
live or dead infected birds. However, you should avoid bare-handed contact when
handling any dead animal. If you must pick up a dead bird, use gloves or an inverted
plastic bag to place the bird’s carcass (body) in a garbage bag.
What
should I do if I find a dead bird?
State and local agencies have different policies for collecting
and testing birds, so check with your state health department or state wildlife
agency for information about reporting dead birds in your area. Wildlife
agencies routinely investigate sick or dead bird events if large numbers are
impacted. This type of reporting could help with the early detection of
illnesses like West Nile virus or Avian influenza (bird flu), known to cause
death in birds. If local authorities tell you to simply dispose of the bird’s
carcass (body), don’t handle it with your bare hands. Use gloves or an inverted
plastic bag to place the carcass in a garbage bag, which can then be disposed
of in your regular trash .
Call or contact the United States Department of
Agriculture’s (USDA) Wildlife Services office at
1-866-4-USDA-WS (1-866-487-3297).
Why
did some states and local areas stop collecting dead birds to test for West
Nile virus?
West Nile virus is found in all 48 contiguous states (not in
Alaska) and the virus circulates in mosquitoes and birds every year. Because
West Nile virus is well established, some states and local jurisdictions are no
longer collecting dead birds for testing. Instead, they have chosen to shift
staff and funding resources away from testing of dead birds to other areas of
West Nile virus surveillance and control.
Mosquito
Control
Everyone
Can Help Control Mosquitoes
Mosquito control is something anyone can do, ranging from
individual home owners to professionals.
·
You can control mosquitoes in your home.
·
You, your neighbors, and the community can
also take steps to reduce mosquitoes in and around your home and in your
neighborhood.
·
Professionals from local government departments or mosquito
control districts develop mosquito control plans, perform tasks to control
larvae and adult mosquitoes, and evaluate the effectiveness of actions taken.
Integrated
Mosquito Management
Local governments and mosquito control programs often use an integrated
mosquito management (IMM) or integrated vector management (IVM) approach to
control mosquitoes. IMM uses a combination of methods to prevent and control
mosquitoes that spread viruses, like West Nile. IMM uses methods to control
mosquitoes based on an understanding of mosquito biology, the mosquito life
cycle, and the way mosquitoes spread viruses to develop plans for controlling
mosquitoes. IMM uses methods that, when followed correctly, are safe and have
been scientifically proven to reduce mosquito populations.
Everyone can help control mosquitoes.
·
Professionals from local government departments or mosquito control
districts develop mosquito control plans, perform tasks to control larvae and
adult mosquitoes, and evaluate the effectiveness of actions taken.
·
You, your neighbors, and the community can also take steps to reduce
mosquitoes in and around your home and in your neighborhood.
Conduct mosquito surveillance
Mosquito control plans include taking steps to control mosquito populations
before people start getting sick with a virus spread by mosquitoes.
Professionals need to understand what types and numbers of mosquitoes are in an
area. In order to find out this information, mosquito control experts conduct
surveillance. Surveillance activities can include
·
Finding and monitoring places where adult mosquitoes lay eggs. The larvae
that hatch from eggs are found in these same places
·
Tracking mosquito populations and the viruses they may be carrying
·
Determining if EPA-registered insecticides will be effective
These activities help professionals determine if, when, and where control
activities are needed to manage mosquito populations before people start
getting sick. If professionals discover that local mosquitoes are carrying
viruses (like West Nile, or others), they start implementing other activities identified
in their mosquito control plans.
Remove places where mosquitoes lay eggs
Removing places where mosquitoes lay eggs is an important step. Mosquitoes
lay eggs near water because larvae need water to survive. Professionals and the
public can remove standing water to reduce mosquito larvae before they become
adult flying mosquitoes.
·
Professionals at local government agencies and mosquito control districts
may collect and dispose of illegally dumped tires, clean up and maintain public
spaces like parks and greenways, and clean up illegal dumps and roadside trash.
·
You, your neighbors, and community can remove standing water. Once a week,
items that hold water like tires, buckets, planters, toys, pools, birdbaths,
flower pot saucers, and trash containers should be emptied and scrubbed, turned
over, covered, or thrown away.
·
If needed, a community clean up event can be held to remove large items
like tires that collect water.
Control larvae and pupae
Once mosquito eggs hatch, they become
larvae and then pupae. Both larvae and pupae live in standing water. Dumping or
removing standing water in and around your home is one way to control larvae.
For standing water that cannot be dumped or drained, a larvicide can be used to
kill larvae. Larvicides[PDF – 1
page] are products used to kill larvae before they become
biting adults.
The public and professionals can use US Environmental Protection Agency
(EPA)-registered larvicides according to label instructions.
·
Professionals treat water-holding structures and containers in public
places, like storm drains or urns in cemeteries. They may also treat standing
water on private property as part of a neighborhood cleanup campaign.
·
People can treat fountains, septic tanks, and pool covers that hold water
with larvicides.
·
Controlling larvae and pupae before they become adults can minimize
widespread use of insecticides that kill adult mosquitoes.
Control adult mosquitoes
Adult mosquitoes can spread viruses (like
West Nile) that make you sick. When surveillance activities show that adult
mosquito populations are increasing or that they are spreading viruses,
professionals may decide to apply adulticides[PDF – 1
page] to kill adult mosquitoes. Adulticides help reduce the
number of mosquitoes in an area and reduce the risk that people will get sick.
The public and professionals can use US Environmental Protection Agency
(EPA)-registered adulticides according to label instructions.
·
If mosquitoes are spreading viruses over larger areas, professionals spray
adulticides by using backpack sprayers, trucks[PDF – 1 page],
or airplanes[PDF – 1 page]
·
People can buy adulticides and use them inside and outside their homes.
Monitor control programs
To make sure that mosquito control activities are working, professionals
monitor the effectiveness of their efforts to control both larvae and adult
mosquitoes. For example, if an insecticide did not work as well as predicted,
professionals may conduct additional studies on insecticide resistance or
evaluate the equipment used to apply insecticides.
Support
Your Local Mosquito Control Programs
Support your local community mosquito control programs. Mosquito control activities are most often handled at
the local level, such as through county or city government. The type of
mosquito control methods used by a program depends on the time of year, the
type of mosquitoes to be controlled, and the habitat structure. Methods can
include elimination of mosquito larval habitats, application of insecticides to
kill mosquito larvae, or spraying insecticides from trucks or aircraft to kill
adult mosquitoes. Your local mosquito control program can provide information
about the type of products being used in your area. Check with your local
health department for more information. Contact information may be found in the
blue (government) pages of the phone book.
Information
on Aerial Spraying
When
people in a large area are getting sick from a virus spread by mosquitoes, or
when large numbers of mosquitoes are found, airplanes can be used to treat very
large areas with insecticides safely, quickly, and efficiently. This process is
called aerial spraying. Below is more information on aerial spraying.
Aerial Spraying and Mosquito Control
Is aerial spraying an
effective tool for killing mosquitoes?
Aerial treatment of areas with products that rapidly reduce both
adult mosquitoes and their larvae that may carry viruses can be effective.
Repeated aerial applications of insecticide has reduced mosquito populations as
a part of an integrated mosquito management program.
Is aerial spraying
alone the best way to control mosquitoes?
·
Aerial spraying is only one part of the solution for controlling
mosquitoes, but it is the one method that can rapidly reduce the number of
mosquitoes spreading a virus in a large area.
o It is
the most effective method when large areas must be treated quickly.
·
Aerial spraying is used as part of an integrated mosquito control
program to quickly reduce the number of mosquitoes responsible for infecting
people with viruses like West Nile, Zika, dengue, or chikungunya.
·
An integrated mosquito control program includes
o Source
reduction, to eliminate mosquito habitats, such as discarded containers and
rain gutters.
o Structural
barriers, such as screens and enclosed, air-conditioned spaces, if possible.
o Larval
mosquito control using the appropriate methods for the habitat.
o Adult
mosquito control using insecticides.
o Community
education efforts related to preventing mosquito bites by wearing
EPA-registered insect repellents and protective clothing (long-sleeved shirts
and long pants).
Aerial Spraying and Insecticides
How is an insecticide
chosen for use in aerial spraying?
·
State and local officials make the decision on what insecticide(s)
to use for aerial spraying.
·
The decision is based on the results of insecticide resistance
testing in the target area.
Is aerial spraying
experimental?
·
Aerial spraying is not experimental.
·
EPA-registered insecticides are used for aerial spraying.
EPA-registered insecticides have been studied for their effectiveness and
safety when used according to label instructions.
·
Aerial spraying, using Naled and other insecticides, has been used
in many populated areas of the continental United States, including Miami,
Tampa, and New Orleans, to help control mosquitoes.
o In
2014, almost 6 million acres of land in Florida was aerial sprayed with Naled
by mosquito control programs.
Where has Naled been
used?
·
Naled has been extensively used since the 1950s and is currently
applied by aerial and ground spraying to an average of approximately 16 million
acres of the continental United States annually.
·
It is also used for mosquito control following natural disasters,
such as hurricanes and floods. (Human Exposure to Mosquito-Control Pesticides ―
Mississippi, North Carolina, and Virginia, 2002 and 2003, CDC, 2005)
·
In 2004 and 2005, it was used as part of the emergency responses
to Hurricanes Charley, Jeanne, Frances, and Katrina.
·
Naled is currently used in the United States by many local
governments and mosquito control districts, including the Florida Keys Mosquito
Control District, the Lee County Mosquito Control District, and Miami-Dade
County.
·
Historically, Naled has been used in Puerto Rico in attempts to
control dengue.
What happens to Naled
once it is sprayed?
·
Naled starts to degrade (break down) immediately on surfaces, in
water, and in sunlight.
·
The chemical dichlorvos (DDVP) can be created when Naled degrades.
It also breaks down quickly.
·
In small quantities DDVP has not been shown to cause health
problems in people.
·
DDVP does not build up in breast milk or breast tissue.
What is Bti and how
does it work?
·
Bacillus thuringiensis subspecies israelensis (Bti)
is a naturally occurring bacteria found in soils.
·
Bti produces toxins that kill the larvae of mosquitoes and
blackflies when swallowed. The toxins cause death by starvation and only begin
working when swallowed by certain insects (larvae of mosquitoes, blackflies,
and fungus gnats).
·
There are several strains of Bacillus thuringiensis (Bt) that
kill other insect larva like caterpillars and beetles. These are not the same
as Bti.
Can Bti only be
applied through aerial spraying?
·
No, Bti is often applied using methods that are not aerial
spraying.
·
Bti can be applied using truck-mounted or backpack spraying. It
can also be found as dunks or briquettes that can be put in areas of standing
water that cannot be emptied, such as fountains and ornamental ponds, septic
tanks, and unchlorinated pools.
·
Dunks are currently being distributed in Zika prevention kits.
Aerial Spraying and Organic Farming
Is Naled harmful to
crops or livestock?
No. The USDA has determined, under the USDA organic regulations,
that application of Naled for mosquito control will not impact the organic
status of certified organic crops and livestock. Only small amounts of Naled
are used for mosquito control. Spraying Naled will not result in a detectable
presence of Naled or its byproducts on the ground, plants, or animals.
Is Bti harmful to
crops?
Bti is not toxic to people. It has not been shown to make people
sick. When used as directed, Bti can be applied safely to standing water where
mosquitoes lay eggs without causing harm to food crops or water supplies. Bti
is EPA-registered for use in residential, commercial, and agricultural
settings. Organic farming operations use Bti.
Aerial Spraying and Human Health
Is aerial spraying of
insecticides dangerous/harmful to human health?
·
No, during aerial spraying, a small amount of insecticide is
sprayed over an area, about 1 ounce (two tablespoons) per acre or about the
size of a football field.
·
This small amount does not pose a health risk to people or pets in
the area that is sprayed.
·
When aerial spraying is done correctly, it does not cause asthma
attacks.
·
There is a possibility that spraying of a larvicide, like Bti, can
cause eye irritation if a person is outside and looking up when spraying takes
place.
·
EPA-registered products are used for aerial spraying. The label
instructions are followed by a licensed professional.
·
If people prefer to stay inside and close windows and doors when
spraying takes place they can, but it is not necessary.
Does aerial spraying
cause asthma attacks?
·
No, when aerial spraying is done correctly, it does not cause
asthma attacks.
·
When applied according to label instructions, EPA-registered
insecticides do not pose a risk to human health or the environment.
·
Research shows that ultra-low volume (ULV) application for
mosquito control does not increase the risk of asthma for people living in
treatment areas (Karpati et al. 2004, Currier et al. 2005, Duprey et al. 2008).
Will Naled cause
cancer?
·
No, EPA has classified Naled as Group E “Evidence of Non-carcinogenicity
for Humans,” meaning that there is no evidence that it causes cancer in people.
·
During aerial spraying, a small amount of insecticide is sprayed
over an area, about 1 ounce (two tablespoons) per acre or about the size of a
football field.
·
Droplets float in the air and kill adult mosquitoes on contact.
·
Naled starts to degrade (break down) immediately on surfaces, in
water, and in sunlight.
·
EPA conducted risk assessments for Naled and calculated risks
under different exposure scenarios.
·
Because of the very small amount of active ingredient released per
acre of ground during aerial spraying, EPA found that for all scenarios and
exposures were hundreds or thousands of times below an amount that might pose a
health concern.
·
In an evaluation of thousands of people who conducted agricultural
spraying using many types of insecticides, including organophosphates like
Naled, no increased risk of any type of cancer was found during the 7-11 years
of follow up (Schinasi & Leon, 2008).
·
However, at high doses, for example if the person doing the
spraying is exposed to Naled directly in amounts that are well above those for
normal labeled uses, Naled and other organophosphates can overstimulate the
nervous system, causing nausea, dizziness, or confusion. This is why it is very
important that those who actually work with Naled strictly follow label
instructions.
o Severe
high-dose poisoning with any organophosphate can cause convulsions, respiratory
paralysis, and death.
o It is
extremely unlikely that any person would come into contact with this amount of
Naled when it is applied by a licensed professional according to label
instructions.
Will Bti affect human
health?
·
Bti has not been found to pose a health risk to people or pets.
·
There is a possibility that spraying larvicides, like Bti, can
cause eye irritation if a person is outside when spraying takes place.
·
Bti is an EPA-registered insecticide. EPA-registered insecticides
have been studied for their effectiveness and safety when used according to
label instructions.
·
Existing residential and area-wide uses, like aerial or truck
spraying, have been evaluated and found to be safe. Using Bti to kill mosquito
larvae may reduce the risk of getting infected with viruses like West Nile,
Zika, dengue, or chikungunya.
·
If people prefer to stay inside when spraying takes place they
can, but it is not necessary.
Aerial Spraying and Animals
Will aerial spraying
hurt pets and other animals?
·
No, when aerial spraying is done correctly, it does not harm
animals.
·
During aerial spraying, a small amount of insecticide is sprayed
over an area, about 1 ounce (two tablespoons) per acre, or about the size of a
football field.
·
This small amount does not pose a health risk to people or pets in
the area that is sprayed.
·
EPA-registered products are used for aerial spraying. The label
instructions are followed by a licensed professional. If people prefer to bring
pets inside when spraying takes place they can, but it is not necessary.
·
Aerial spraying will not harm fish or animals that live in
the water. People do not need to cover fishponds when spraying takes place. If
a larvicide is sprayed, it is better if ponds are not covered.
Will aerial spraying
kill bees?
·
Aerial spraying can be done in ways that minimize risk to bees.
·
Spraying Naled can kill bees outside of their hives at the time of
spraying; therefore, spraying is limited to dawn or dusk when bees are inside
their hives.
·
Because Naled breaks down quickly, it does not pose a risk to the
honey bee populations.
o Studies
show that honey production between hives in treated and untreated sites did not
show significantly different quantities of honey over the course of a season.
o For
additional protection, urban bee keepers inside the spray zone can cover their
hives when spraying occurs.
·
Although significant exposure to bees would not occur with Naled
application at dawn and dusk, beekeepers can reduce potential exposure to bee
colonies even more by covering colonies and preventing bees from exiting during
designated treatment periods or, if possible, relocating colonies to an
untreated site.
·
The spraying of mosquito larvicides will not impact bees.
Will aerial spraying
kill birds or other animals?
·
No, when aerial spraying is done correctly, it does not harm birds
or other animals.
·
The insecticides used for aerial spraying do not pose risks to
wildlife or the environment.
·
Aerial spraying does not cause long-term harm to the environment
or local ecosystem, even if spraying happens more than once.
·
EPA-registered insecticides used for aerial spraying break down
rapidly in the environment, and it displays low toxicity to birds and mammals.
·
Aerial spraying will not harm coquis or fish or animals that live
in the water. People do not need to cover fish ponds when spraying takes place.
If a larvicide is sprayed, it is better if ponds are not covered.
Will Bti affect
animals or wildlife?
·
No, Bti does not pose a risk to other mammals, birds, or aquatic
life, including coqui frogs in Puerto Rico and the U.S. Virgin Islands. The
toxins it produces only begin working once swallowed by certain insects (larvae
of mosquitoes, blackflies, and fungus gnats).
Aerial Spraying and the Environment
Will aerial spraying
pollute water?
·
No, when aerial spraying is done correctly, it does not pollute
water.
·
Research shows that, when applied according to label instructions,
EPA-registered insecticides sprayed in low levels (about two tablespoons per
acre [4,046 square meters]) does not cause long-term harm to the environment or
local ecosystem, even if spraying happens more than once.
Will chemicals from
aerial spraying contaminate soil?
·
No, when chemicals used in aerial spraying are used correctly,
they will not contaminate soil.
·
Aerial spraying does not cause harm to the environment or local
ecosystem, even if spraying happens more than once.
·
When applied according to label instructions, EPA-registered
insecticides do not pose a risk to human health or the environment.
Is Bti harmful to
crops or water supplies?
Bti is not toxic to people. It has not been shown to make people
sick. When used as directed, Bti can be applied safely to standing water where
mosquitoes lay eggs without causing harm to food crops or water supplies. Bti
is EPA-registered for use in residential, commercial, and agricultural
settings. Organic farming operations use Bti.
Multiple Bti products are available for use. Some can be used by
pest control professionals in certain drinking water storage containers (e.g.,
cisterns) while others are not EPA-registered for that use. Always follow label
instructions. It is important to follow the label for any Bti product to ensure
that the product is being used correctly.
For
Vector Control Professionals
Clinical
Evaluation & Disease
Diagnosis
& Reporting
West Nile virus (WNV) disease should be considered in any person
with a febrile or acute neurologic illness who has had recent exposure to
mosquitoes, blood transfusion, or organ transplantation, especially during the
summer months in areas where virus activity has been reported. The diagnosis
should also be considered in any infant born to a mother infected with WNV
during pregnancy or while breastfeeding. More
information on WNV in pregnancy and breastfeeding is available here.
In addition to other more common causes of encephalitis and
aseptic meningitis (e.g. herpes simplex virus and enteroviruses), other
arboviruses (e.g., La Crosse, St. Louis encephalitis, Eastern equine
encephalitis, and Powassan viruses) should also be considered in the
differential etiology of suspected WNV illness.
WNV disease is a nationally notifiable condition. All cases should
be reported to local public health authorities in a timely manner. Reporting
can assist local, state, and national authorities to recognize outbreaks and to
implement control measures to reduce future infections.
Clinical Signs & Symptoms
The incubation period for WNV disease is typically 2 to 6 days but
ranges from 2 to 14 days and can be several weeks in immunocompromised people.
An estimated 70-80% of human WNV infections are subclinical or
asymptomatic. Most symptomatic persons experience an acute systemic febrile
illness that often includes headache, weakness, myalgia, or arthralgia; gastrointestinal
symptoms and a transient maculopapular rash also are commonly reported. Less
than 1% of infected persons develop neuroinvasive disease, which typically
manifests as meningitis, encephalitis, or acute flaccid paralysis.
·
WNV meningitis is clinically indistinguishable from viral
meningitis due to other etiologies and typically presents with fever, headache,
and nuchal rigidity.
·
WNV encephalitis is 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 acute flaccid paralysis is usually clinically and
pathologically identical to poliovirus-associated poliomyelitis, with damage of
anterior horn cells, and may progress to respiratory paralysis requiring
mechanical ventilation. WNV poliomyelitis often presents as isolated limb
paresis or paralysis and can occur without fever or apparent viral prodrome.
WNV-associated Guillain-Barré syndrome and radiculopathy have also been reported
and can be distinguished from WNV poliomyelitis by clinical manifestations and
electrophysiologic testing.
Rarely, cardiac dysrhythmias, myocarditis, rhabdomyolysis, optic
neuritis, uveitis, chorioretinitis, orchitis, pancreatitis, and hepatitis have
been described in patients with WNV disease.
Most women known to have been infected with WNV during pregnancy
have delivered infants without evidence of infection or clinical abnormalities.
In the best-documented, confirmed congenital WNV infection, the mother
developed neuroinvasive WNV disease during the twenty-seventh week of
gestation, and her neonate was born with cystic lesions in brain tissue and
chorioretinitis. One infant who apparently acquired WNV infection through
breastfeeding remained asymptomatic. Guidelines for the evaluation of fetal and neonatal WNV
infections.
Clinical Evaluation
Routine clinical laboratory studies are generally nonspecific. In
patients with neuroinvasive disease, CSF examination generally shows
lymphocytic pleocytosis, but neutrophils may predominate early in the course of
illness. Brain magnetic resonance imaging is frequently normal, but signal
abnormalities in the basal ganglia, thalamus, and brainstem may be seen in
patients with encephalitis, and in the anterior spinal cord in patients with
poliomyelitis.
Outcomes
Most patients with non-neuroinvasive WNV disease or WNV meningitis
recover completely, but fatigue, malaise, and weakness can linger for weeks or
months. Patients who recover from WNV encephalitis or poliomyelitis often have
residual neurologic deficits. Among patients with neuroinvasive disease, the
overall case-fatality ratio is approximately 10%, but it is significantly
higher for patients with WNV encephalitis and poliomyelitis than WNV
meningitis.
Recent studies have raised questions about the possible
persistence of WNV infection and subsequent renal disease. More information is available here.
Diagnostic
Testing
WNV
Antibody Testing
Laboratory diagnosis is generally accomplished by testing of serum
or cerebrospinal fluid (CSF) to detect WNV-specific IgM antibodies.
Immunoassays for WNV-specific IgM are available commercially and through state
public health laboratories.
WNV-specific IgM antibodies are usually detectable 3 to 8 days
after onset of illness and persist for 30 to 90 days, but longer persistence
has been documented. Therefore, positive IgM antibodies occasionally may
reflect a past infection. If serum is collected within 8 days of illness onset,
the absence of detectable virus-specific IgM does not rule out the diagnosis of
WNV infection, and the test may need to be repeated on a later sample.
The presence of WNV-specific IgM in blood or CSF provides good
evidence of recent infection but may also result from cross-reactive antibodies
after infection with other flaviviruses or from non-specific reactivity.
According to product inserts for commercially available WNV IgM assays, all
positive results obtained with these assays should be confirmed by neutralizing
antibody testing of acute- and convalescent-phase serum specimens at a state
public health laboratory or CDC.
WNV IgG antibodies generally are detected shortly after IgM
antibodies and persist for many years following a symptomatic or asymptomatic
infection. Therefore, the presence of IgG antibodies alone is only evidence of
previous infection and clinically compatible cases with the presence of IgG,
but not IgM, should be evaluated for other etiologic agents.
Plaque-reduction neutralization tests (PRNTs) performed in
reference laboratories, including some state public health laboratories and
CDC, can help determine the specific infecting flavivirus. PRNTs can also
confirm acute infection by demonstrating a fourfold or greater change in
WNV-specific neutralizing antibody titer between acute- and convalescent-phase
serum samples collected 2 to 3 weeks apart.
Other testing for WNV disease
Viral cultures and tests to detect viral RNA (e.g., reverse
transcriptase-polymerase chain reaction [RT-PCR]) can be performed on serum,
CSF, and tissue specimens that are collected early in the course of illness
and, if results are positive, can confirm an infection. Immunohistochemistry
(IHC) can detect WNV antigen in formalin-fixed tissue. Negative results of
these tests do not rule out WNV infection. Viral culture, RT-PCR, and IHC can
be requested through state public health laboratories or CDC.
Additional Information about Laboratory Testing
Contact your state or local health department for assistance with
diagnostic testing. They can assist you with determining if samples should be
sent to the CDC Arbovirus Diagnostic Laboratory for further
testing.
Treatment
There is no specific treatment for WNV disease; clinical
management is supportive. Patients with severe meningeal symptoms often require
pain control for headaches and antiemetic therapy and rehydration for
associated nausea and vomiting. Patients with encephalitis require close
monitoring for the development of elevated intracranial pressure and seizures.
Patients with encephalitis or poliomyelitis should be monitored for inability
to protect their airway. Acute neuromuscular respiratory failure may develop
rapidly and prolonged ventilatory support may be required.
Various drugs have been evaluated or empirically used for WNV
disease, as described
in a review of the literature for health care providers[PDF – 11
pages]. However, none have shown specific benefit to date.
The National Institutes of Health maintains a registry of federally and
privately supported clinical trials conducted in the United States and around
the world.
Prevention
No WNV vaccines are licensed for use in humans. In the absence of
a vaccine, prevention of WNV disease depends on community-level mosquito
control programs to reduce vector densities, personal protective measures to
decrease exposure to infected mosquitoes, and screening of blood and organ
donors. Personal protective measures include use of mosquito repellents,
wearing long-sleeved shirts and long pants, and limiting outdoor exposure from
dusk to dawn. Using air conditioning, installing window and door screens, and
reducing peridomestic mosquito breeding sites, can further decrease the risk
for WNV exposure.
Blood and some organ donations in the United States are screened
for WNV infection; healthcare professionals should remain vigilant for the
possible transmission of WNV through blood transfusion or organ
transplantation. Any suspected WNV infections temporally associated with blood
transfusion or organ transplantation should be reported promptly to the
appropriate state health department.
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