West Nile FAQ's
What is it?
West Nile Virus (WNV) is a virus disease of humans and animals
that is usually transmitted by mosquitoes. Mosquitoes
obtain the virus when they bite infected birds, which is where
the virus is maintained in nature. WNV is closely related to St.
Louis encephalitis, but it normally causes a milder disease in
people.
Historical Background
Worldwide: WNV was first identified in 1937 in a woman in
Africa. The earliest epidemic of WNV was reported from Israel in
1950. Since then, additional epidemics have occurred in Europe,
Africa, the Middle East and North America. United States:
WNV was not known to occur in North America before 1999. It was
apparently introduced into New York City during the summer of
that year. By the end of 1999, there had been 25 equine(horse)
cases and 62 human cases, of which seven people died. The
disease has spread rather rapidly since the initial epidemic in
the New York City area. In 2000, there were another 21 human
cases from three northeastern states and 60 more equine cases
from seven northeastern states. WNV-positive birds were reported
in 13 states, the southernmost being North Carolina. In 2001,
WNV spread throughout most of the eastern half of the United
States. WNV-positive birds were reported from 28 states. There
were 738 equine cases in 20 states and 66 human cases in 10
states. Southeastern states that reported human WNV cases were
Florida, Georgia, Alabama and Louisiana. The continued expansion
of WNV suggests that it is firmly established in the United
States. Louisiana: WNV spread from New York to Louisiana
much faster than originally predicted. The first sign of the
disease was a WNV-positive blue jay reported in July of 2001.
Afterward, there were nine equine cases from four southern
parishes and one human case in Jefferson Parish (New Orleans
area). As of April 1, there had already been one equine case and
one positive bird reported in 2002. WNV is expected to remain in
Louisiana.
How did WNV spread so fast?
The rapid spread of WNV can probably be attributed to infected
migratory birds.
Which animals can be infected with WNV?
Birds are the most commonly infected. Other animals include
equines (horses, mules, donkeys), bats, chipmunks, skunks,
squirrels and domestic rabbits. From a veterinary perspective,
horses are the most at risk. WNV infections have occurred in
dogs and cats, but these cases are extremely rare, so WNV is not
a serious threat to dogs and cats.The Vector: How is the disease transmitted?
WNV is transmitted to people and animals by infected mosquitoes.
Although ticks have been reported to transmit WNV, too,
mosquitoes are by far the most important vector (carrier).
Which mosquitoes can transmit WNV, and are they present in
Louisiana?
More than 25 species of mosquitoes in the United States have
been found infected with VVNV. Mosquitoes of the genera Culex
are thought to be the most important group and potentially the
main vectors. Louisiana mosquitoes that have been found infected
with WNV either in Louisiana or elsewhere are Aedes albopictus,
Culex restuans, Culex quinquefasciatus, Culex saliniarus,
Culiseta melanura, Psorophora ferox, Ochlerotatus triseriatus
and Aedes vexans. This indicates that mosquitoes in Louisiana
can transmit WNV.
The normal disease cycle.
WNV is usually maintained in nature by birds and mosquitoes.
Mosquito-to-bird transmission and bird-to-mosquito transmission
both occur when mosquitoes take a blood meal from birds.
Although many birds die from the disease, they probably serve as
the natural reservoir for the virus. Humans and other animals
become involved in the cycle when they are bitten by an infected
mosquito. They are, however, thought to be dead-end hosts,
meaning they cannot pass the virus on to other mosquitoes, as
birds do.
The Reservoir: How are birds affected?
WNV has been isolated in more than 70 species of birds found
dead in the United States. Certain bird species, such as crows,
appear to be much more susceptible than others. Large die-offs
of crows have occurred in some areas. Mortality is less frequent
in other bird species, and these birds probably serve as
carriers of the WNV. Most birds are thought to be infectious for
only four to five days, but some migratory birds can travel
several hundred miles in this short period.
Can people get WNV from birds?
There is no documented evidence that people can get WNV from
handling live or dead infected birds. VVNV is transmitted by
infected mosquitoes.
The Disease: WNV in People
Most people infected with WNV will not become ill or severely
ill. Less than 10% of the people who are infected will develop
serious illness. Healthy children and young adults are in the
low-risk category, but people older than 50 are considered to be
at a higher risk to develop a serious illness. Symptoms occur
three to 15 days after the initial infection. Mild cases usually
result in slight fever and headaches. More severe cases result
in high fever, head and body aches, disorientation, tremors and
possibly convulsions. Extreme cases can result in paralysis or
death. Of those people who develop a serious illness, the
mortality rate ranges from 3% to 15%.
Is a human vaccine available?
No. Can people get WNV from horses or other infected animals?
No. People may become infected when an infected, mosquito bites
them. There is no documented evidence of animal-to-man
transmission of WNV.
The Disease WNV in horses.
Some horses that become infected do not show signs of illness.
Clinical signs of illness in horses may include weakness,
staggering, mild tremors and a sleepy appearance. The
mortality rate appears to be 35% to 50%. In reaching a
diagnosis, a veterinarian must consider several diseases
including other types of virus encephalitis: '' rabies and
equine protozoal ''moldy corn poisoning, myeloencephalitis. The
veterinarian can submit a blood sample for an encephalitis test.
Is a WNV vaccine available to protect horses?
Yes. Horses vaccinated for the first time must receive two
injection dosages at a three- to four-week interval. The two
dose series is essential to obtain an effective immune response.
A booster shot should be given in the spring each year thereafter. Booster
shots may be indicated at six-month intervals. Currently, WNV vaccine is available only through
veterinarians.
Will other encephalitis vaccines such as Eastern Equine (EEE),
Western Equine (WEE) and Venezuelan Equine (VEE) protect my
horse from WNV?
No. Your horse must be vaccinated with a WNV vaccine.
Currently, there is a five-in-one equine vaccine which protects
horses against five different encephalitises, including West
Nile virus. Ask your veterinarian for details on this
vaccine.
What should I do if I suspect WNV symptoms in my horse?
Contact a local veterinarian to determine the exact cause of
illness. WNV symptoms can mimic other types of equine illness.
Some horses that become infected do not show signs of illness.
Therefore, the safest course of action is to have your horse
vaccinated.
Can Mosquito Control (or other government agency) diagnose my
horse for free?
No. Testing for West Nile Virus and other diseases is
considered part of a veterinarian's care.
Can a horse get WNV frvm another infected horse?
There is no documented evidence of animal-to-animal
transmission. WNV is transmitted to horses by infected
mosquitoes.
Can people get WNV from caring for or handling an infected
horse?
There is no documented evidence of animal-to-people
transmission. WNV is transmitted to people by infected
mosquitoes.
How can people protect themselves from WNV?
Since there is no approved vaccine, the best way to protect
yourself from WNV is to protect yourself from mosquito bites.
1. Avoid outdoor activity during periods of heavy mosquito
activity, normally in the early morning and late
afternoon/evening hours.
2. Use an effective repellent such as DEET to protect exposed
skin areas when working or playing outdoors.
3. Eliminate standing pools of water and empty containers that
hold water around the home. Mosquitoes breed in water.
4. Approved, general use insecticides can be applied around the
perimeter of the house and the home to eliminate resting areas
for mosquitoes.
5. Small, portable foggers are available to homeowners for a
reasonable price. They can be used to kill live mosquitoes
around the home premises, but they provide no residual control.
6. Wear long sleeves and pants when working outdoors to
discourage mosquito bites.
How can people protect their horses from WNV?
1. Have your horse vaccinated with a WNV vaccine as directed
above.
2. Insecticides will give some protection to horses from
mosquito bites, but this does not guarantee protection from WNV.
Insecticides are not totally effective, and they must be applied
regularly at short intervals. They do not provide total
protection, because horses are constantly exposed to mosquito
activity outdoors.
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