West Nile Virus

WEST NILE VIRUS DISEASE

Definition:
West Nile virus is an infection transmitted by mosquitoes. If you become infected with West Nile virus, you may not experience any signs or symptoms or you may experience only minor ones, such as fever and mild headache. However, some people who become infected with West Nile virus develop a life-threatening illness that includes inflammation of the brain.

Mild signs and symptoms of a West Nile virus infection generally go away on their own. But severe signs and symptoms — such as a severe headache, disorientation or sudden weakness — require immediate attention.

Exposure to mosquitoes where West Nile virus exists increases your risk of getting West Nile virus. Protect yourself from mosquitoes by using mosquito repellent and wearing clothing that covers your skin to reduce your risk.

Symptoms:
Most have no symptoms
Most people infected with the West Nile virus have no signs or symptoms.

Mild infection signs and symptoms
About 20 percent of people develop a mild infection called West Nile fever. Common signs and symptoms of West Nile fever include:

Fever
Headache
Body aches
Fatigue
Skin rash (occasionally)
Swollen lymph glands (occasionally)
Eye pain (occasionally)

Serious infection signs and symptoms
In less than 1 percent of infected people, the virus causes a serious neurological infection. Such infection may include inflammation of the brain (encephalitis) or of the brain and surrounding membranes (meningoencephalitis). Serious infection may also include infection and inflammation of the membranes surrounding the brain and spinal cord (meningitis), inflammation of the spinal cord (West Nile poliomyelitis) and acute flaccid paralysis — a sudden weakness in your arms, legs or breathing muscles. Signs and symptoms of these diseases include:

High fever
Severe headache
Stiff neck
Disorientation or confusion
Stupor or coma
Tremors or muscle jerking
Lack of coordination
Convulsions
Pain
Partial paralysis or sudden weakness

Signs and symptoms of West Nile fever usually last a few days, but sign and symptoms of encephalitis or meningitis can linger for weeks, and certain neurological effects, such as muscle weakness, may be permanent.

When to see a doctor
Mild symptoms of West Nile fever usually resolve on their own. If you experience signs or symptoms of serious infection, such as severe headaches, a stiff neck or an altered mental state, seek medical attention right away. A serious West Nile virus infection generally requires hospitalization.

Causes: West Nile virus transmission cycle
Infection transmitted by mosquitoes
Typically, West Nile virus spreads to humans and animals via infected mosquitoes. Mosquitoes become infected when they feed on infected birds. You can't get infected by touching or kissing a person with the virus.

Most West Nile virus infections occur during warm weather, when mosquito populations are active. The incubation period — the period between when you're bitten by an infected mosquito and the appearance of signs and symptoms of the illness — ranges from three to 14 days.

West Nile virus is present in areas such as Africa, parts of Asia and the Middle East. It first appeared in the United States in the summer of 1999 and since then has been found in all 48 contiguous states.

Other possible routes of transmission
In a few cases, West Nile virus may have been spread through other routes, including organ transplantation and blood transfusion. However, blood donors are screened for the virus, substantially reducing the risk of infection from blood transfusions.

There have also been reports of possible transmission of the virus from mother to child during pregnancy or breast-feeding, but these have been rare and not conclusively confirmed.

Risk factorsYour overall risk of getting West Nile virus depends on these factors:

Time of year. The majority of cases in the United States have occurred between the months of July and September.
Geographic region. West Nile virus has been reported in most of the United States but the Western and Midwestern states have had the highest incidence rates.
Time spent outside. If you work or spend time outdoors, you have a greater chance of being bitten by an infected mosquito.

Risk of serious infection
Even if you are infected, your risk of developing a serious West Nile virus-related illness is extremely small — less than 1 percent of people who are bitten become severely ill. And most people who do become sick recover fully. You're more likely to develop a severe or fatal infection based on:

Age. Adults over the age of 50 are at higher risk of infection.
Health. Those who have a weakened immune system, such as from receiving an organ transplant, are at greater risk of infection.

Preparing for your appointmentIf you experience signs and symptoms of a severe West Nile virus infection — such as a high fever, a severe headache, a stiff neck, disorientation or sudden muscle weakness — see your doctor right away or go to an urgent care center. If you are seriously ill, you may need to be hospitalized.

What you can do
Make a list to take with you that includes:

Detailed descriptions of your symptoms
A record of your recent activities or travel to an area where West Nile virus is prevalent
Information about your past medical problems
Information about the medical problems of your parents or siblings
Questions you want to ask the doctor

What to expect from your doctor
In addition to listening to your description of symptoms, your doctor will perform a physical exam. Your doctor will also take into account whether it's mosquito season and whether he or she has seen other cases of West Nile virus infection recently.

Your doctor may take blood samples to be analyzed for West Nile virus antibodies. To be the most useful, these samples must be taken within the first eight days after symptoms appear. In some cases, your doctor may recommend other tests, as well. If necessary, your doctor may send you to a hospital for supportive therapy.

Tests and diagnosisYour doctor can confirm the presence of West Nile virus in your body by analyzing a sample of your blood or the fluid surrounding your spinal cord (cerebrospinal fluid). If your doctor suspects a serious, West Nile virus-related illness such as meningitis or encephalitis, you may undergo a lumbar puncture or brain-imaging tests.

Laboratory tests. If you are infected, a blood test may show a rising level of antibodies to the West Nile virus. Antibodies are immune system proteins that attack foreign substances, such as viruses. A positive ribonucleic acid (RNA) test for the West Nile virus also is an indicator that you have the virus.
Lumbar puncture (spinal tap). The most common way to diagnose meningitis is to analyze the cerebrospinal fluid surrounding your brain and spinal cord. A needle inserted between the lower vertebrae of your spine is used to extract a sample of fluid for laboratory analysis. The fluid sample may show an elevated white cell count — a signal that your immune system is fighting an infection — and antibodies to the West Nile virus.
Brain tests. In some cases, an electroencephalography (EEG) — a procedure that tests your brain's activity — or an MRI scan can help detect brain inflammation.

Treatments and drugs:
Supportive therapy
Most people recover from West Nile virus without treatment. Over-the-counter pain relievers can help ease mild headaches and muscle aches.

There's no direct cure for encephalitis or meningitis, but you may need supportive therapy in a hospital with intravenous fluids and medicines to prevent other types of infections.

Interferon therapy
Scientists are investigating interferon therapy — a type of immune cell therapy — as a treatment for encephalitis caused by West Nile virus. Some research shows that people who receive interferon may recover better than those who don't receive the drug, but more study is needed.

Prevention:
Your best bet for preventing West Nile virus and other mosquito-borne illnesses is to avoid exposure to mosquitoes and eliminate mosquito-breeding sites. To help control West Nile virus:

Eliminate standing water in your yard. Mosquitoes breed in pools of standing water.
Unclog roof gutters.
Empty unused swimming pools.
Change water in birdbaths at least weekly.
Remove old tires or any unused containers that might hold water and serve as a breeding place for mosquitoes.

To reduce your own exposure to mosquitoes:

Avoid unnecessary outdoor activity when mosquitoes are most prevalent, such as at dawn, dusk and early evening.
Wear long-sleeved shirts and long pants when you go into mosquito-infested areas.
Apply mosquito repellent with DEET to your skin and clothing. Choose the concentration based on the hours of protection you need — the higher the percentage (concentration) of the active ingredient, the longer the repellent will work. Avoid using DEET on the hands of young children, in case they put their hands in their mouths, or on infants under 2 months of age. When outside, cover your infant's stroller or playpen with mosquito netting.

A vaccine is available to protect horses from West Nile virus. No vaccine is available for humans, but work to develop a human vaccine is under way.

Q. and A. on West Nile Virus

By Anahad O'Connor : NY Times : August 23, 2012

The outbreak of West Nile virus this year has spread to nearly every state and is shaping up to be the largest one on record since the first human cases were reported in the United States in 1999.

But for all the fear and concerns in some parts of the country, health officials say the reality is that most people who become infected will not have any symptoms, and of those who do, only a fraction will develop severe illness. To find out more about the disease and the factors fueling the current outbreak, we spoke with Dr. Erin Staples, a medical epidemiologist at the Centers for Disease Control and Prevention.

Q.

Is it true that many of the symptoms of West Nile are easily overlooked? How many people probably have it and don't know it?

A.

From studies we know that only about one in every five people who get infected with West Nile will actually develop symptoms. The most common ones are fever, headaches, body ache, joint pain, vomiting, diarrhea and rash. A lot of people who develop symptoms usually just wait it out at home. Or they'll go to a medical doctor and end up recovering from their illness and feeling much better within several weeks. Sometimes, people will complain of fatigue or report feeling not quite themselves for several months.

Q.

How does a person know if he or she has a more serious form of the illness? What symptoms should prompt you to see a doctor?

A.

Symptoms of severe neurological disease due to West Nile virus infection can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.

Less than 1 percent of people who are infected will develop such symptoms of more serious neurological illness, like encephalitis or meningitis, which is inflammation of the brain or surrounding tissue.

But people with the serious neurological symptoms are more likely to seek treatment and find out that they have it. With the serious neurological symptoms, about 10 percent of people will die as a result.

Q.

How do you find out if you have West Nile? Is there a test?

A.

People who have symptoms that concern them should see a health care provider. If they think they have West Nile, they can have their blood tested for the presence of antibodies or, in more severe cases that affect the central nervous system, a doctor can take samples of the cerebrospinal fluid that surrounds the brain and spinal cord.

Usually people are hospitalized if they have more serious symptoms.

Q.

Are certain groups at higher risk?

A.

Anyone who is outdoors during times when mosquitoes are active is at a higher risk - so that means people who go outside at dusk and dawn who haven't done anything to prevent getting bitten, like using repellents or wearing pants and long sleeves.

We do know that there are certain groups that are also at risk of having more severe disease. The groups we've identified include people over the age of 50, and people who have medical conditions like cancer, diabetes, hypertension, kidney disease and organ transplants.

We know this from data we've collected from state health departments. For a lot of these high-risk groups, it probably deals with their ability to fight infection. You may have people with cancer, for example, who are receiving drugs that inhibit their immune cells. Someone with diabetes may not be able to fight the infection as well as an otherwise healthy person.

With people over the age of 50, it's most likely that as you age your immune cells are not as robust. We do have a larger proportion of people with encephalitis in the older age group. But anybody who's out there and not using measures to prevent mosquito bites could be at risk for getting West Nile.

Q.

How widespread is the outbreak, and how are you keeping track of it?

A.

The C.D.C. reports numbers once a week. We take a snapshot, and the states know to report to us by Tuesday morning at 3 a.m.

So as of Tuesday we knew that there were 1,118 cases of West Nile being reported from throughout the United States, and that included 41 deaths.
Right now, we have received reports of West Nile virus infections or activity in people, birds or mosquitoes in 47 states. It's pretty much widespread in the continental United States. The states that have not reported any are Hawaii and Alaska, which have never reported any West Nile activity, and then Vermont. Vermont has previously reported cases, just none so far this year.

Q.

What is the regional breakdown of cases? Are most in Texas?

A.

Almost half of our cases have been reported in Texas, so that is the most affected region at this point. But about 75 percent of our cases have been reported from five states. The first is Texas, the next is Mississippi, Louisiana, then South Dakota and Oklahoma. The central region of the United States is the main area reporting the most cases, but most states are being affected, just to varying degrees.

Q.

How does this compare with other West Nile outbreaks?

A.

We definitely have received reports from state health departments of earlier and greater West Nile activity, particularly in the central states. It's more than we've seen in recent years, and we're not quite sure why. Essentially there are several factors that play a role, including the weather, the number and types of mosquitoes that spread the virus, birds that also spread the virus, what people are doing to prevent it, and whether there's community-based spraying. All of those things may determine the size and location of an outbreak. So it makes it very difficult to predict from year to year where we may see West Nile virus outbreaks, because these things change.

Q.

Why is this outbreak so severe? Is it the biggest?

A.

There is some thought that the unusual mild winter we had, the early spring and the hot summer, may have fostered some conditions that are favorable to breeding mosquitoes that spread West Nile virus.

What we can say right now is this is the biggest outbreak. If we look at the number of cases reported to the C.D.C. over the last 10 years, through the third week of August, we've had an average of 390 West Nile cases reported each year, and that ranged from a low last year of 77 cases to a high in 2004 of 832 cases.

So now, having more than 1,000 cases reported to us this year through the third week of August, we're up from what we've traditionally seen in the past. However, we don't know how this is going to translate in the end of the year, for instance, if there's going to be significant changes. Let's say New York goes into an early frost this year. That could truncate transmissions.

Q.

What steps can people take to protect themselves?

A.

Use insect repellents when you go outdoors. Wear long sleeves and pants to prevent mosquito bites at dusk and dawn. Install or repair screens or windows to prevent mosquitoes from getting inside your home. Empty any containers of standing water around your home - things like flower pots, kiddie pools, buckets and sometimes even gutters, which can have standing water in them.