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West Nile Virus


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West Nile Virus can be transmitted by something as typical as a mosquito bite.

Although the chances of contracting the virus are quite low, people who live or plan to travel in mosquito infested areas may feel better protected if certain precautionary measures are taken.

Repellents containing DEET and mosquito netting are still the best forms of protection from mosquito bites, along with a mosquito zapper racket to kill any others before they bite.

West Nile Virus originated in remote areas such as Africa, Eastern Europe, West Asia, and the Middle East. Until 1999 it had not previously been documented in the Western Hemisphere. While we are not sure where the U.S. and Canadian virus originated it is thought to have come from strains found in the middle-east. See West Nile Virus Statistics.


Studies conducted by the Centers for Disease Control and Prevention have documented nine hundred fifty-four human cases of West Nile Virus in the United States in 2002. Illinois, Louisiana, Michigan and Mississippi were the areas most affected. Infected birds have also been found in Canadian provinces such as Ontario, Manitoba, Saskatchewan and Quebec. See mosquito facts.


Mosquitoes contract West Nile Virus when they feed on infected birds. The infected blood circulates within a mosquito’s salivary glands for a few days. When a human or animal is bitten by an infected mosquito it may take three to fourteen days for West Nile Virus symptoms to show up. Not everyone who contracts the virus will have a severe reaction. West Nile Virus symptoms can be very mild ranging from a small fever and flu-like symptoms or it can result in permanent neurological affects or even death.

West Nile virus can infect both humans and certain animals including horses, many types of birds and certain other mammals. Over one hundred ten species of birds have been known to be infected. Many people worry that the virus may be contagious, however there is no evidence to suggest that it can be spread from person to person or from animal to person. It has only been documented spreading by infected mosquitoes.

The History of West Nile Virus

The West Nile virus was first isolated in a woman in the West Nile district of Uganda in 1937. In 1957, in an outbreak amongst elderly patients in Israel, the virus was recognized as a cause of severe human meningitis or encephalitis (inflammation of the brain and spinal cord). Since then, the disease has spread throughout much of the world including Africa, Europe, the Middle East, Central Asia and most recently, North America. It has been detected in humans, animals and mosquitoes in all of these regions.

The West Nile Virus first appeared in North America in 1999 in New York City. Since then, it has been found in 47 States. The West Nile virus was first reported in Canada in August 2001 when it was discovered in dead birds and mosquitoes in Southern Ontario. It has been reported in five provinces: Ontario, Quebec, Manitoba, Saskatchewan and Alberta.

Today, we know that the West Nile virus is carried by birds and transmitted by mosquitoes. A human being or animal is infected with the disease when they are bitten by a mosquito that is also infected.

The chances of a person being infected with the West Nile Virus is very low and of those infected, less than 1% will become seriously ill. The very best way to avoid being infected is to avoid getting bitten by mosquitoes Here are some tips on how you can protect yourself from the West Nile Virus and prevent the disease from spreading:

  • Use bug repellent when outdoors
  • Wear protective clothing
  • Report any dead birds in your area
  • Eliminate areas around your home where water can collect as they can become ideal breeding ground for mosquitoes.

Preventive Measures

It is obvious to all that mosquitoes are annoying; but now many people are concerned about the health risks associated with mosquito bites?

Consider buying the best mosquito trap you can afford. Take the following precautionary measures to significantly reduce your chances of being bitten by any mosquito including one that is potentially infected.

  • Wear long sleeved shirts and long pants if possible when you are outdoors.
  • When you are taking an infant or young child outside use mosquito netting over the infant carrier or carriage.
  • Make sure to repair broken screen doors or windows to keep your residence mosquito-free.
  • Drain sources of standing water in places like buckets, barrels, tires, bird baths and such to reduce the amount of mosquitoes that breed around your home.
  • Peak times for mosquitoes are at dawn, dusk and in the early evening. Stay indoors during these times if you are in a mosquito infested area.

Using mosquito nets and repellents containing DEET are a few ways to protect ourselves from contracting West Nile Virus.

Mosquito Repellents

A mosquito repellent containing DEET can be applied to the skin to protect from mosquito bites but must be re-applied for longer periods of protection. The more DEET a repellent contains the longer time it can protect you from mosquito bites. A higher percentage of DEET in a repellent does not mean that your protection is better-just that it will last longer. Products containing about 24% DEET are effective for an average of 5 hours against mosquitoes, after that it should be re applied for the extra time you plan to be outdoors.

Facts about DEET

  • DEET should never be applied to the face; mosquito netting worn over the face can best protect you.
  • It should never be applied to sunburned or irritated skin and should be washed off after returning indoors.
  • Never apply it to pets; they can get seriously ill if they ingest it by licking or cleaning themselves.
  • Clothing should also be sprayed because mosquitoes can bite through thin clothing.
  • DEET should never be used on children under six months of age.
  • A repellent containing ten percent DEET should be used on a young child.

Mosquito Netting

Millions of people around the world are infected with mosquito-borne illnesses such as dengue, malaria, yellow fever and various forms of encephalitis each year according to the World Health Organization. There are many different types of mosquito netting including head and bed nets that can protect you and your family from the mosquitoes and other nasty insects in your area or while travelling abroad. They come in a variety of mesh sizes and can be bought already treated with an insecticide for extra protection.

You can also get your community involved and develop an effective mosquito control plan.

West Nile Virus Symptoms

West Nile Fever

Approximately twenty percent of the people who contract the West Nile Virus will develop fever. This is the mild form of the Virus that is not life-threatening and usually lasts for a few days.

Symptoms of West Nile Fever

Fever, headache, body ache, swollen lymph glands and occasionally a rash on the trunk of the body are common West Nile Virus symptoms. These symptoms take as little as three to twelve days to show up and a few days to disappear.

One in one hundred and fifty people infected with the virus will experience severe West Nile Virus symptoms. Those who are more susceptible to the more serious effects of the virus are the elderly and those with compromised immune systems.

West Nile Encephalitis

A more serious form of the virus that affects people primarily in the late summer or early fall. However, it can be transmitted year-round in the southern climates where temperatures are milder. There is no vaccine available for the West Nile Virus however several companies are working to develop one.

Symptoms of West Nile Encephalitis

Headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis are common symptoms. These types of West Nile Virus symptoms have been known to last several weeks, and usually leave permanent neurological effects.


Although found mainly in birds, West Nile Virus has been identified in other animals such as horses, cats, bats, chipmunks, skunks, squirrels, and domestic rabbits. As the virus multiplies in the animal’s system it crosses the blood-brain barrier and eventually resulting in inflammation of the brain.

West Nile Virus Statistics

West Nile virus is a progressively common and dangerous disease. Since 1999, hundreds of people have been infected or killed by it. The severity of the disease makes it important for everyone to have a comprehensive understanding of it. Researching West Nile virus information can teach you how to protect yourself and your loved ones from the fatal illness.

Here is a list of important West Nile Virus information and statistics:

According to the National Institute of Allergy and Infectious Diseases, scientists have identified at least 40 mosquito species that can transmit West Nile virus.

Scientists donít know how long West Nile virus has been in North America, but they estimate that the virus has probably been in the eastern United States since 1999.

In 1999, 61 cases of severe disease and 7 deaths occurred in the New York area. No reliable estimates are available for the number of cases of West Nile that occur worldwide. Source

Chances of Infection

It is estimated that 20% of the people who become infected will develop West Nile fever, leaving 80% of those infected to not experience any type of illness. It is also estimated that 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease.

Tick Borne West Nile Virus

Most people know that mosquitoes are carriers of the West Nile Virus, but many of us are unaware that ticks are also important contributors. Tick borne West Nile Virus is a serious cause for concern in North America. While mosquitoes remain the major contributors in the transmission of the disease, ticks have recently been discovered to play a significant role. Birds that carry the virus frequently become infested with ticks, which in turn become infected with the virus. Subsequently, the infected tick transmits the virus to other birds, creating an elevated level of infected birds. Mosquitoes that bite infected birds become carriers of tick borne West Nile Virus.

Symptoms of West Nile Virus

West Nile Virus and tick borne West Nile Virus are derived from the same viral string; therefore, their symptoms are the same. Many individuals who become infected with the virus exhibit from very mild to no symptoms at all. However, when infection does cause the person to become ill, reactions usually consist of flu-like symptoms such as:

  • fever
  • chills
  • nausea
  • headaches
  • body aches

In the rare and more serious cases known as West Nile Encephalitis, the disease presents a rapid onset of symptoms such as:

  • confusion
  • moderate to severe headaches
  • very high fever
  • muscle weakness
  • loss of consciousness

In the very severe cases, West Nile Encephalitis can induce a state of coma, cause permanent brain damage, and/or death.

What safety precautions can you take?

Although once thought to be a temporary epidemic in North America, the West Nile Virus has spread so rapidly that it is now deemed to be a permanent recurring seasonal illness, much like the flu. A tempting method to eradicate the virus at this point would be to eliminate its natural host, birds. However, not only is that solution impossible, but it also brings no hope or guarantee as birds are migratory.

The best defence against contracting West Nile Virus or tick borne West Nile Virus is to avoid being bitten by mosquitoes and avoid areas where ticks flourish. During the summer months, this is easier said than done, but the following precautions are definitely helpful:

  • Wear long sleeves and pants outdoors
  • Cover your exposed skin with DEET insect repellent
  • Spray your clothing with a high level of DEET insect repellent
  • Eliminate all stagnant waters on your property (the ideal breeding ground for mosquitoes)

If you see a tick on your skin, remove it with tweezers by its head (it would be the closest part to your skin). Never crush or swat the tick as this action would encourage it to “latch on” even more tightly. To date, there have been no reported case of tick borne West Nile virus as a result of a direct bite from a tick to a human, but ticks do transmit other illnesses such as Lyme disease.

If you think you might have contracted West Nile Virus, or tick borne West Nile Virus, it is recommended that you consult a doctor immediately.

Facts About West Nile Virus in Horses

West Nile virus in horses is not very common and is usually nothing to worry about as long as early precautions are taken to treat the infected horse. Like the West Nile virus in humans, the disease is not transmittable from horse to horse or from horse to person. The only known way that a horse can become infected with the West Nile virus is by being bitten by an infected mosquito. Through the insect’s bite, the virus is injected into the horse’s blood system, multiplies, and can cause illness. West Nile virus in horses becomes dangerous only if the virus infects the brain. This can lead to brain inflammation and thereafter interfere with the normal function of the animal’s central nervous system. Once the horse’s central nervous system is seriously affected, possible death can ensue.

Symptoms of the West Nile virus in horses

Signs that could indicate that a horse is infected with the West Nile virus include: stumbling, weakness in hind limbs, inability to stand, listlessness and head shaking. However, some infected horses show no signs at all.

How should a horse with the West Nile virus be treated?

There is no reason to destroy or even isolate a horse that is infected with the West Nile virus. Most horses will fully recover from the illness. Treatment for the horse should be consistent with standard veterinary practice for animals infected with a viral disease.

Can horses be vaccinated against the West Nile virus?

The answer is yes. A vaccination against the West Nile virus for horses has recently been approved by the FDA for veterinary use only. The vaccination is called West Nile Innovator (Fort Dodge) and it helps horses develop immunity to West Nile infections. However, the effectiveness of the vaccine has yet to be determined.

West Nile Virus Symptoms in Birds

West Nile virus is a serious illness which is transmitted by a mosquito that carries the disease. A mosquito becomes infected after biting an infected bird; thereafter, it may pass the virus on to other birds, humans, or animals. The West Nile virus cannot be transferred from a bird to a human. When a human contracts the virus, symptoms such as fever, headache, nausea, rash and swollen glands, may become apparent soon after. However, it is not the same case with birds. West Nile virus symptoms in birds are usually non-existent. Birds do not usually show signs of infection until the last stage of the disease, which is encephalitis or inflammation of the brain. An infected bird may appear drowsy, be unable to fly or walk properly; it may even have problems standing upright. The West Nile virus has been reported in over 150 species of birds in North America.

Prevention of the Virus in Birds

There is no surefire way to obliterate the virus presently, but there are certain ways to reduce the likelihood of its presence in your area. Water in birdbaths should be changed every 48 hours to prevent mosquito eggs from hatching and potentially passing on the disease to birds and humans. Investigate your property and eliminate any source of standing water, which can attract mosquitoes; properly chlorinate pools and other ornamental ponds on your property. If you notice a bird that appears to demonstrate the symptoms of infection, immediately call your local veterinarian or wildlife organization. They can advise you on how to capture, handle and transport the bird to a recommended place. Crows, ravens, magpies and blue jays are known to be the most susceptible, and the most likely to exhibit the recognizable symptoms of West Nile virus. Therefore, if you are aware of an increase in the deaths of these three types of birds in your area, the presence of West Nile virus is probable.

Handling Infected Birds

Although West Nile virus symptoms in birds are not always or easily detectable, there are other existing diseases in birds that are noticeable and communicable to humans. Always proceed with caution when approaching or handling a wild bird that appears disoriented, sick or lifeless. There is no sufficient evidence that a human can contract the West Nile virus by simply touching an infected bird. However, if you find a dead bird on or near your property, do not risk touching it with bare hands. Use thick, leak-proof, rubber gloves, and pick it up with a shovel, bag or other tool, being careful not to puncture or scratch your skin. Dispose of the carcass according to your local city’s bylaws. You may also wish to place a call to your local wildlife organization to inquire about their West Nile virus testing resources. After handling the bird, remember to wash your hands thoroughly with soap and water.

America West Nile Virus Outbreak 2012

While West Nile Virus (WNV) and other mosquito-borne illnesses are not uncommon around the world, they have gained a lot more attention in recent years, as the number of cases and the spread of these diseases has grown substantially.

North America was strongly affected by the West Nile outbreak in 2012, with Texas taking the worst of it.

Contributing Factors

The West Nile outbreak of 2012 was the worst in recent history, with over 1,600 cases and 66 deaths in the United States. A number of different factors lead to this epidemic:

  • Potential virus mutation, indicated by the manifestation of different symptoms, as opposed to previous years
  • Sporadic rains, following a year of drought; hurricane and flood conditions throughout the southeast United States
  • Negligence and apathy in regards to following disease prevention and protection guidelines, including the clearing of standing water.

As opposed to NWV, which manifested with flu-like symptoms, 2012s virus seems to have additional neurological effects, making for a more deadly strain for two main reasons. First, without the exhibition of flu-like symptoms, the illness might go unnoticed, allowing it to get further along before treatment is sought. Secondly, an increased occurrence of neurological symptoms means an increased likelihood of meningitis or encephalitis, two of the complications that make West Nile Virus so deadly.

Hurricane Isaac

The Center for Disease Control (CDC) and many communities along the Gulf Coast were on the lookout for a surge in the number of West Nile cases following Hurricane Isaac’s landfall in Louisiana. Thunderstorms caused power outages, leaving over 200,000 people homeless – crippling the ability to defend against mosquito-borne illnesses due to loss of suitable clothing, window screens, insect repellents, and other safety necessities – but this was not the greatest threat posed by the storm.

The biggest challenge that Isaac presented was the simple fact that there was a seemingly endless extent of standing water – and not just in Louisiana and Mississippi, where the storm hit hardest, but also from Texas to the eastern seaboard, where the associated thunderstorms struck. Standing water was ground zero for mosquitoes, an ideal breeding center for insects that lay eggs in warm, stagnant waters, which precisely describes the kind of conditions that were prevalent in the southeastern United States dring this time. While the CDC was helping to clear out standing water in the areas worst hit, other regions reported water depth of five feet; moreover, with a primary levee burst in the area with the most water, there was nowhere for that overflow to go.

This disaster meant that the greatest danger of the hurricane season was yet to come, as hundreds of thousands were left unprotected, and increased mosquito breeding added up to a recipe guaranteed to worsen the West Nile outbreak.

Halting Mosquito Breeding

Mosquitoes, primarily the Culex mosquitoes (although the west coast of the United States has found other species of mosquitoes that carry the virus, the Culex is the primary disease carrier throughout the US), can grow from egg to full-grown adult in as little as 10 days. They are particularly problematic because they can reproduce in even the smallest amount of water, which means that constant vigilance is a must in order to spot and remove standing water sources. While they need relatively still water in which to thrive, they can survive in conditions of moderate agitation, as long as the surface of the water is predominantly calm (fountains that run on timers, for instance, still provide a fertile breeding ground).

Many communities are addressing the mosquito breeding problem by placing mosquito fish (Gambusia affinis) or guppies into freshwater sources, as these types of fish feed on mosquito larvae and thereby can keep a small pool or pond from producing millions of mosquitoes every week. Agitating standing water and skimming the surface will also help to destroy the larvae and eggs, but removing the standing water altogether is the best solution.

WNV Treatments

For a medical look at West Nile Virus in North America, read this article from the USGS National Wildlife Health Center:

While scientists have yet to develop a vaccine for West Nile Virus, researchers at Utah State University have recently made a breakthrough when they discovered the exact part of the brain that WNV affects. With this knowledge, it will be easier to develop treatment options and perhaps a vaccine in the future–not only for West Nile Virus, but potentially for a range of viruses, as the mechanism that causes death is unknown in the vast majority of viral brain diseases.

Whilst the current West Nile outbreak has alarmed a lot of people, there are a number of things that you can do to offset the risks–staying informed is the first step towards keeping this danger at bay!

Understanding West Nile Virus Transmission Methods

The dangerously infectious West Nile virus (WNV) is kept alive in a continuous cycle of mosquito-to-bird contacts and mosquito to offspring transference. A mosquito ingests the virus by feeding on the blood of a contaminated bird or an infected female mosquito transfers the virus to its eggs.  Typical scientific findings regarding the West Nile virus transmission have determined that female mosquitoes, once infected, can pass on the illness in the following manners:

  • Horizontally, to a person or mammal by taking a “blood meal” and thereafter transferring the virus vertically to her offspring during gestation.
  • Vertically, to her young during egg-laying, with no prior horizontal transference.
  • Horizontally, to a person or mammal, without further transferring the virus vertically.

About Horizontal Transmission

Within a few days of having fed off an infected bird, the West Nile virus is distributed throughout the female mosquito’s bloodstream and ultimately finds its way to the secretion glands. The infected mosquito then transmits the virus directly to a host (human or mammal) via its saliva as it bites the flesh.  This method of West Nile virus transmission is called horizontal.

Although horizontal transmission is of significant importance to sustaining the virus in nature during the year’s warm summer months and into the fall, a further process is required to preserve its existence during the cold winter months when mosquitoes become inactive. This other method of transmission is known as vertical.

About Vertical Transmission

The West Nile virus can be passed down from one generation to the next within the mosquito population by way of vertical transference (female adult to offspring), or in literal terms, transovarial transmission. This biological method of transfer occurs when the infected adult female mosquitoes infect their young as they develop inside the egg. Upon hatching, the larvae are already WNV-positive and able to transmit the virus when they grow into adulthood. Because the female mosquito is the only sex that bites, finding the virus in a male is only possible through vertical transmission.

Field and Facility Testing

Vertical West Nile virus transmission gives way to horizontal transmission, allowing the disease to endure the winter hibernation of the mosquito and launch a fresh wave of infection come springtime. This theory (and a subject under much debate for some years now) has been recently put to the test with natural and laboratory studies.

Reports from research conducted in nature have concluded that infected female mosquitos of the “Culex pipiens” genus can in fact vertically transmit the West Nile virus to its descendants, permitting the strain to remain effective while withstanding the northern winter climate. The virus quarantine has been collected from both adult males and nulliparous females (those who have not yet spawned) in the field over the summer. The same virus was also drawn from female mosquitoes resting in standing water the following winter. End results have indicated that vertical transmission is likely happening by course of nature.

Indoor lab studies have gone on to further prove the argument by manually injecting adult female mosquitoes with WNV. After a week of incubation, they were released for the next phase of testing. The procedure has essentially shown evidence of same: that even after a controlled period of hibernation, the vertically transmitted newborns of the contaminated female were still capable of infecting small test subjects with the West Nile virus.


When used side-by-side, the two West Nile virus transmission methods create a vicious loop. Together, they are responsible for the increase of infection cases over the summer months, which seem to spike especially in August, and the reintroduction of WNV the following spring.

The Culexbreed of mosquito (a.k.a. the common North American mosquito) is considered the primary carrier of the West Nile virus strain, and responsible for the widespread of the ever-present, potentially harmful disease.


Mosquitoes – This site offers weekly updates about West Nile Virus topics.

Mosquito Netting Info – Mosquito netting and various mosquito-borne diseases such as malaria, West Nile virus and Dengue fever and their methods of prevention are explored here.

Mosquito – Wikipedia’s outake on the mosquito.

West Nile Virus – Keep Kids Healthy – Learn more about the West Nile Virus, including transmission, immunity, prevention, symptoms, testing, dead birds, pesticides and vaccines.

PubMed Health – National Center for Biotechnology Information.

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