National West Nile Virus Info-line
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Symptoms, Diagnosis and Treatment

• What are the symptoms of West Nile virus infection?
• Who is at risk for serious health effects from West Nile virus?
• How do doctors diagnose West Nile virus infection in their patients?
• How are blood samples tested for West Nile virus?
• What treatments are available for people with West Nile virus?
• Is there a vaccine for West Nile virus?
• What are the long-term effects of West Nile virus?

What are the symptoms of West Nile virus infection?

Many people infected with West Nile virus have no symptoms and do not get sick or have only mild symptoms. When infection does cause illness, symptoms will usually appear within two to 15 days. The extent and severity of symptoms vary widely from person to person.

In mild cases, there may be flu-like symptoms, including fever, headache and body aches. Some people may also develop a mild rash, or swollen lymph glands.

Some individuals have weaker immune systems, and they are at greater risk of developing symptoms and health effects that are more serious, including meningitis, encephalitis and acute flaccid paralysis. Meningitis is inflammation of the lining of the brain or spinal cord. Encephalitis is inflammation of the brain itself. Acute flaccid paralysis is a polio-like syndrome that can result in the loss of function of one or more limbs. These conditions can be fatal.

For people with more severe illness, symptoms could include the rapid onset of severe headache, high fever, stiff neck, nausea, difficulty swallowing, vomiting, drowsiness, confusion, loss of consciousness, lack of coordination, muscle weakness and paralysis. Other symptoms that have been identified include movement disorders, parkinsonism, poliomyelitis-like syndrome and muscle degeneration. Anyone who has a sudden onset of these symptoms should seek immediate medical attention.

Who is at risk for serious health effects from West Nile virus?

While persons of any age or health status can be at risk of developing serious health effects from West Nile virus, the overall risk of serious health effects increases with age. People with weaker immune systems are considered to be at greater risk for serious health effects.

People at higher risk for serious health effects from West Nile virus include:

• people with chronic diseases, such as cancer, diabetes, alcoholism, or heart disease;
• people that require medical treatment that may weaken the immune system, i.e. chemotherapy.

Because West Nile virus can cause severe complications for people of any age and any health status, it is extremely important to reduce the risk of getting bitten by mosquitoes. Anyone exposed to mosquitoes in an area where West Nile virus has been detected is at some degree of risk for infection.

How do doctors diagnose West Nile virus infection in their patients?

The first thing doctors look for are symptoms of West Nile virus infection. The type of symptoms and their severity can vary widely from case to case. In mild cases, there may be flu-like symptoms, including fever, headache and body aches. Some people may also develop a mild rash or swollen lymph glands.

While persons of any age or health status can be at risk of developing serious health effects associated with West Nile virus infection, including meningitis, encephalitis, and acute flaccid paralysis, the overall risk of serious health effects increases with age. Meningitis is inflammation of the lining of the brain or spinal cord. Encephalitis is inflammation of the brain itself. Acute flaccid paralysis is a polio-like syndrome that can result in the loss of function of one or more limbs. In these cases, symptoms include the rapid onset of severe headaches, high fever, stiff neck, nausea, difficulty swallowing, vomiting, drowsiness, blurred vision or deterioration in eyesight, confusion, loss of consciousness, lack of coordination, muscle weakness and paralysis. If a doctor suspects that a patient has West Nile virus, a blood test will be conducted to confirm the diagnosis.

How are blood samples tested for West Nile virus?

The most common tests employed require blood samples to be collected and tested for the presence of antibodies to West Nile virus. Two categories of antibody blood tests for WN virus exist:

a) front-line testing and
b) confirmatory testing.

Front-Line Testing: Doctors may use the results of front-line tests to modify treatments and therapies for patients. The primary front-line test used in Canada in 2003 was the ELISA test although other front-line tests such as the hemagglutination inhibition test were also available. Commercial ELISA tests appear to have worked well but they are currently available only by Special Access and have not been licensed in Canada to date.

There are two types of ELISA (IgM and IgG) tests that can be used, one of which (IgM) may not always require a second test to be performed when the first specimen is positive, so it can potentially speed up the reporting of positive results. If West Nile cases are already confirmed in a given locality and antibodies of a certain level are demonstrated in the first blood sample, it is acceptable for doctors to consider this to be a case of West Nile and to modify patient treatment accordingly.

Confirmatory Testing: these tests are done to provide researchers and public health officials with important information about West Nile virus such as:

• whether the virus is turning up again in an area where human cases were previously recorded;
• whether the virus has spread to new areas;
• the geographical distribution of the virus as it spreads;
• new ways the virus can be spread (i.e. through blood transfusions); and,
• who may be at greater risk for serious health effects.

Confirmatory tests are generally done on initial cases in a given jurisdiction or on patients with histories of travel to other areas whose positive front-line test results may be due to cross-reactions with related members of the West Nile family of flaviviruses, such as St. Louis encephalitis or Dengue virus.

Once West Nile virus has been definitively proven to be active in an area and infection in humans has occurred, it is no longer necessary to do a confirmatory test on each case. It is important to note that doctors do not need the results of confirmatory tests in order to treat and care for their patients.

What treatments are available for people with West Nile virus?

There is no specific treatment, medication, or cure for West Nile virus. Serious cases are treated with supportive therapies to ease symptoms and prevent secondary infections. These cases may require hospital or nursing care.

Is there a vaccine for West Nile virus?

At this time there is no licensed vaccine to protect people against West Nile virus.

For several years, the National Institute of Allergy and Infectious Diseases (NIAID) in the United States has supported research to develop a vaccine against West Nile virus. Through both intramural research and research grants to investigators throughout the United States, NIAID supports the development of several vaccine approaches, including developing chimeric vaccines (mixing pieces from more than one virus into a single vaccine, naked DNA vaccines, or vaccines containing cocktails of individual West Nile proteins. These candidate West Nile virus vaccines are currently at various states of development, including one that is expected to enter Phase 1 human trials by late summer 2004, pending Food and Drug Administration (FDA) approval. The Public Health Agency is monitoring these developments closely.

A vaccine licensed in the U.S. does not receive an automatic license in Canada. Manufacturers or importers who wish to sell a vaccine in Canada must apply to Health Canada for a license. They must also provide Health Canada with scientific evidence that the vaccine is safe and effective when used as directed.

For more information on West Nile virus vaccine development in the United States please see the NIAID West Nile virus fact sheet.

What are the long-term effects of West Nile virus?

Because West Nile virus is an emerging disease, the long-term effects are not fully understood. Studies to date show that some people with serious symptoms and health effects recover completely, while others experience prolonged health problems. These problems can include:

• physical effects, such as long-term muscle weakness and paralysis, fatigue and headache;
• cognitive effects, such as confusion, depression, problems with concentration and memory loss;
• functional effects, such as difficulty with preparing meals, going out, shopping, etc.

Scientists do not know why some people recover while others continue to have varying degrees of health problems.

Important Notices