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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?


 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 from 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.