The West Nile Virus CEUS

Q. What are the symptoms of West Nile virus (WNV) infection?
A. Infection with WNV can be asymptomtic (no symptoms), or can lead to West Nile fever or severe West Nile disease.

It is estimated that about 20% of people who become infected with WNV will develop West Nile fever. Symptoms include fever, headache, tiredness, and body aches, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands. While the illness can be as short as a few days, even healthy people have reported being sick for several weeks.

The symptoms of severe disease (also called neuroinvasive disease, such as West Nile encephalitis or meningitis or West Nile poliomyelitis) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. It is estimated that approximately 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease. Serious illness can occur in people of any age, however people over age 50 and some immunocompromised persons (for example, transplant patients) are at the highest risk for getting severely ill when infected with WNV.

Most people (about 4 out of 5) who are infected with West Nile virus will not develop any type of illness (an asymptomatic infection), however you cannot know ahead of time if you'll get sick or not when infected.

Q. What is the incubation period in humans (i.e., time from infection to onset of disease symptoms) for West Nile disease?
A. Usually 2 to 15 days.

Q. How long do symptoms last?
A. Symptoms of West Nile fever will generally last a few days, although even some healthy people report having the illness last for several weeks. The symptoms of severe disease (encephalitis or meningitis) may last several weeks, although neurological effects may be permanent.

Q. What is meant by West Nile encephalitis, West Nile meningitis, West Nile poliomyelitis, “neuroinvasive disease” and West Nile fever?
A. The most severe type of disease due to a person being infected with West Nile virus is sometimes called “neuroinvasive disease,” because it affects a person's nervous system. Specific types of neuroinvasive disease include: West Nile encephalitis, West Nile meningitis, West Nile meningoencephalitis and West Nile poliomyelitis. Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord, meningoencephalitis refers to inflammation of the brain and the membrane surrounding it, and poliomyelitis refers to an inflammation of the spinal cord.

West Nile Fever is another type of illness that can occur in people who become infected with the virus. It is characterized by fever, headache, tiredness, aches and sometimes rash. Although the illness can be as short as a few days, even healthy people have been sick for several weeks.

Q. If I have West Nile Fever, can it turn into West Nile encephalitis?
A. When someone is infected with West Nile virus (WNV) they will typically have one of three outcomes: No symptoms (most likely), West Nile fever (WNF in about 20% of people) or severe West Nile disease, such as meningitis or encephalitis (less than 1% of those who get infected). If you develop a high fever with severe headache, consult your health care provider.

West Nile fever is characterized by symptoms such as fever, body aches, headache and sometimes swollen lymph glands and rash. West Nile fever generally lasts only a few days, though in some cases symptoms have been reported to last longer, even up to several weeks. West Nile fever does not appear to cause any permanent health effects. There is no specific treatment for WNV infection. People with West Nile fever recover on their own, though symptoms can be relieved through various treatments (such as medication for headache and body aches, etc.).

Some people may develop a brief, WNF-like illness (early symptoms) before they develop more severe disease, though the percentage of patients in whom this occurs is not known.

Occasionally, an infected person may develop more severe disease such as “West Nile encephalitis,” “West Nile meningitis” or “West Nile meningoencephalitis.” Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord, and meningoencephalitis refers to inflammation of the brain and the membrane surrounding it. Although there is no treatment for WNV infection itself, the person with severe disease often needs to be hospitalized. Care may involve nursing IV fluids, respiratory support, and prevention of secondary infections.

Q. I think I have symptoms of West Nile virus. What should I do?
A. Contact your health care provider if you have concerns about your health. If you or your family members develop symptoms such as high fever, confusion, muscle weakness, and severe headaches, you should see your doctor immediately.

Q. How do health care providers test for West Nile virus?
A. Your physician will first take a medical history to assess your risk for West Nile virus. People who live in or traveled to areas where West Nile virus activity has been identified are at risk of getting West Nile encephalitis; persons older than 50 years of age have the highest risk of severe disease. If you are determined to be at high risk and have symptoms of West Nile encephalitis, your provider will draw a blood sample and send it to a commercial or public health laboratory for confirmation.

Q. How are human cases of WNV diagnosed?
A. West Nile virus (WNV) infection can be suspected in a person based on clinical symptoms and patient history. Laboratory testing is required for a confirmed diagnosis.

The most commonly used WNV laboratory test measures antibodies that are produced very early in the infected person. These antibodies, called IgM antibodies, can be measured in blood or cerebrospinal fluid (CSF), which is the fluid surrounding the brain and spinal cord. This blood test may not be positive when symptoms first occur; however, the test is positive in most infected people within 8 days of onset of symptoms.

A test for WNV IgM-antibody is used by CDC, state and local public health labs and increasingly at private laboratories. When testing is conducted at private laboratories, the health department or CDC will often confirm results in their own laboratories before officially reporting WNV cases.

In some instances, health departments may conduct or request additional testing from CDC before officially reporting a case to CDC's ArboNET Surveillance System. The state or CDC reference laboratory may repeat the initial IgM-antibody testing.

A state may also perform or ask CDC to perform an additional, different test on a specimen. This latter test (plaque reduction neutralization test [PRNT]) is usually performed when:

These additional tests require growth of the virus and may take a week or longer (plus shipping time) to conduct. The results from the PRNT are often needed before CDC considers a human WNV infection confirmed.

Q. How does CDC decide when to report a case of WNV?
A. CDC reports a case of WNV once a state officially reports and verifies that case to CDC.

The timing of the official report to CDC, relative to onset of symptoms in a person, is variable and depends on when an individual first seeks medical care and the extent of the laboratory testing, as described above, that the state determines is necessary before reporting.

At any given time, in addition to the official case count reported by CDC, there may be additional suspect cases under investigation or in various stages of testing, including supplemental or confirmatory laboratory testing.

Q. How many of the human WNV cases are being confirmed by the CDC laboratories?
A. When WNV was first found in the United States in 1999, the CDC reference laboratory confirmed all human cases of WNV. Through a comprehensive, CDC-sponsored laboratory training program, most states are now able to perform the initial blood tests to identify IgM-antibody in the blood or CSF of suspect human WNV infections, and many state laboratories are also able to perform the more involved PRNT. The CDC reference lab is called upon for confirmatory testing by fewer and fewer states; although the increased activity of WNV still requires that many tests be performed at the CDC reference laboratory.

Q. How is West Nile encephalitis treated?
A. There is no specific treatment for West Nile virus infection. In more severe cases, intensive supportive therapy is indicated, often involving hospitalization, intravenous fluids, airway management, respiratory support (ventilator), prevention of secondary infections (pneumonia, urinary tract, etc.), and good nursing care.

Q.What role do commercial laboratories play in diagnosing people with West Nile virus infection?

A.When a person goes to see a health care provider, and has symptoms of a West Nile illness a specimen may be sent to a commercial laboratory to determine if the person has been infected by West Nile virus. The tests used in commercial labs check for antibodies to the virus (the body’s response to infection). The results of the test will be sent to the doctor and the state health department will be informed if the results are positive. There is no specific treatment available for West Nile virus infection, so the diagnosis will not necessarily change the way the person is being treated but it will let the doctor know that he/she does not have to investigate another cause of illness, and it will help the health department know where the virus is active in order to focus prevention measures.

The state health department may choose to accept the positive results from the commercial lab, or they may choose to test the sample again in the state health department laboratory for confirmation of the infection. The state health department will report the case to CDC.

A. The tests used in commercial labs are modeled on the tests created by CDC and used at CDC and in state public health laboratories. This is the first year that many of these tests have been widely used in commercial labs, and laboratories are learning more about the specific measurements used in each test. Often, a second test will be done to confirm the infection. State health departments, the FDA (which licenses and regulates medical tools such as these tests), the association of Public Health Laboratories and CDC are all engaged in monitoring new commercial tests, and are committed to working with industry to make these tests as accurate and useful as possible.

A.A “false positive” occurs when an initial tests indicates that a person does have a West Nile infection, but a later, more specific tests indicates that the person does not actually have the infection. While it is important to health department and CDC to get an accurate idea of where people are being infected in order to focus prevention and control efforts, the result does not have a great impact on the individual person. There is no specific treatment that the person would receive due to West Nile virus infection. The person may want to work with their physician to see if another cause of the illness needs to be identified.

Q. Is there a vaccine available to protect humans from West Nile virus?
A. No. Currently there is no WNV vaccine available for humans. Many scientists are working on this issue, and there is hope that a vaccine will become available in the next few years.

Q. Should people take the West Nile virus vaccine that is licensed for use in horses?
A. No. This vaccine has not been studied in humans and could be harmful. The effectiveness of this vaccine in preventing West Nile virus infections in horses has yet to be fully evaluated, and its effectiveness in humans is completely unknown. Veterinary vaccines are not manufactured with the same rigorous quality and purity standards required of human vaccines, nor are they required to undergo the extensive field testing required of human vaccines before they are licensed. For these reasons, veterinary vaccines and other veterinary drugs should never be used in humans.

Q. What risk does West Nile virus illness during pregnancy present to an unborn child?
A. Based on the limited number of cases studied so far, it is not yet possible to determine what percentage of West Nile virus infections during pregnancy result in infection of the unborn child or medical problems in newborns.

In 2002, one case of transplacental (mother-to-child) transmission of West Nile virus was reported. In this case, the infant was born with West Nile virus infection and severe medical problems. However, it is unclear whether West Nile virus infection caused these problems or whether they were due to other causes (see MMWR Dec 20, 2002).

After the report of this case, CDC and state and local health departments started a registry to monitor birth outcomes among women with West Nile virus illness in pregnancy. Three additional pregnancies in which the expectant mother became infected with West Nile virus were detected and evaluated in 2002; none of these 3 resulted in fetal infection. In one additional case it remains unclear whether the fetus was infected because testing was incomplete.

In 2003 and 2004, the registry identified 77 women who acquired West Nile virus illness while pregnant. Seventy-one of these women delivered live infants, 2 had elective abortions, and 4 miscarried in the first trimester.

From 2005 through 2008, CDC will continue to gather clinical and laboratory information on birth outcomes of women with West Nile virus illness during pregnancy. Pregnant women who think they may have become infected with West Nile virus should contact their private health care providers. Clinicians who are aware of West Nile virus infections of pregnant women are encouraged to report such cases by calling their state or local health departments, or by contacting CDC, telephone 970-221-6400. For more information see the section on Clinical Guidance.

Due to concerns that mother-to-child West Nile virus transmission can occur with possible adverse health effects, pregnant women should take precautions to reduce their risk for West Nile virus and other mosquito-borne infections. This can be done by avoiding mosquitoes, using protective clothing, and using an EPA-registered repellent (one that has been reviewed for safety and efficacy by the US EPA). CDC recommends repellents containing DEET or picaridin on skin and clothing, and permethrin on clothing. Oil of lemon eucalyptus (active ingredient: p-menthane-3,8-diol [PMD]) is another recommended option, but is not as long-lasting. (See Using Repellent Safely for more information.)

Pregnant women who become ill should see their health care provider, and those who have an illness consistent with acute West Nile virus infection should undergo appropriate diagnostic testing.

Additional clinical information on West Nile virus infection during pregnancy can be found in these recent publications:

Q. Where can I get more detailed clinical information about West Nile virus in pregnancy?
A. More information on issues that may be helpful to clinicians working with West Nile virus can be found on the Clinical Guidance page.

Q. Are infants at higher risk than other groups for illness with West Nile virus?
A. No. West Nile virus illnesses in children younger than 1 year old are infrequent. Since 1999 only 18 of the 15,401 cases reported to CDC were in children younger than one year of age.

Q. Can West Nile virus be transmitted through breast milk?
A. Based on a 2002 case in Michigan, it appears that West Nile virus can be transmitted through breast milk. A new mother in Michigan contracted West Nile virus from a blood transfusion shortly after giving birth. Laboratory analysis showed evidence of West Nile virus in her breast milk. She breastfed her infant, and three weeks later, her baby's blood tested positive for West Nile virus. Because of the infant's minimal outdoor exposure, it is unlikely that infection was acquired from a mosquito. The infant was most likely infected through breast milk. The child was healthy, and did not have symptoms of West Nile virus infection.

Q. If I am pregnant or breastfeeding, should I use insect repellents containing DEET or picaridin?
A. Yes. Insect repellents help people reduce their exposure to mosquito bites that may carry potentially serious viruses such as West Nile virus, and allow them to continue to play and work outdoors. In pregnant or breastfeeding women, there are no reported adverse events following use of repellents containing DEET or picaridin. Click here for more information about using repellents safely.

Q. Should I continue breastfeeding if I am symptomatic for West Nile virus?
A. Because the health benefits of breastfeeding are well established, and the risk for West Nile virus transmission through breastfeeding is unknown, the new findings do not suggest a change in breastfeeding recommendations.
Lactating women who are ill or who are having difficulty breastfeeding for any reason should, as always, consult their physicians.

Q. Should I continue breastfeeding if I live in an area of West Nile virus transmission?
A. Yes. Because the health benefits of breastfeeding are well established, and the risk for West Nile virus transmission through breastfeeding is unknown, the new findings do not suggest a change in breastfeeding recommendations.

Q. If I am breastfeeding, should I be tested for West Nile virus?
A. No. There is no need to be tested just because you are breastfeeding.

Q. How many cases of West Nile disease in humans have occurred in the U.S.?
A. Our Statistics, Surveillance, and Control page contains maps showing the distribution of West Nile virus-related human disease cases, by state, in the U.S. in 2005.

Please see CDC's current case count for the number and nature of human cases of West Nile virus-related disease reported in the U.S. in 2005.

In 2004, there were 2539 human cases of WNV disease reported, including 100 deaths. For a report of cases by clinical syndrome and by state, please see the 2004 human disease cases.

In 2003, there were 9862 human cases of WNV disease, including 264 deaths. Cases were reported throughout much of the US; for a report of cases by each state please refer to the 2002 human case count. In 2001, there were 66 human cases of severe disease and 9 deaths. In 2000, 21 cases were reported, including 2 deaths in the New York City area. In 1999, 62 cases of severe disease, including 7 deaths, occurred in the New York area.

No reliable estimates are available for the number of cases of West Nile encephalitis that occur worldwide.

Q. What proportion of people with severe illness due to West Nile virus die?
A. Among those with severe illness due to West Nile virus, case-fatality rates range from 3% to 15% and are highest among the elderly. Less than 1% of people who become infected with West Nile virus will develop severe illness -- most people who get infected do not develop any disease at all.

Q. How can a person test positive for WNV infection at a blood bank, but not be considered a "case" by CDC?
A. A WNV "case" is a person who has become ill and been confirmed to have WNV infection. This infection might be either West Nile Fever, a mild illness with fever, or West Nile encephalitis or meningitis, more severe illnesses. Blood donors who do not become ill and do not develop symptoms are counted in a separate category because they are not considered "cases."

Q. How do people get infected with West Nile virus (WNV)?
A. The main route of human infection with West Nile virus is through the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. The virus eventually gets into the mosquito's salivary glands. During later blood meals (when mosquitoes bite), the virus may be injected into humans and animals, where it can multiply and possibly cause illness.

Additional routes of human infection became apparent during the 2002 West Nile epidemic. It is important to note that these other methods of transmission represent a very small proportion of cases. Investigations have identified WNV transmission through transplanted organs and through blood transfusions. See Blood Transfusions and Transmission: Questions and Answers.

There is one reported case of transplacental (mother-to-child) WNV transmission. This case is detailed in MMWR Dec 20, 2002. There is also one reported case of transmission of WNV through breast-milk. See Questions and Answers concerning WNV and breastfeeding for more information on this topic.

Although transmission of WNV and similar viruses to laboratory workers is not a new phenomenon, two recent cases of WNV infection of laboratory workers have been reported. These cases are detailed in MMWR Dec 20, 2002.

Q. What is the basic transmission cycle of West Nile virus?
A. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. Infected mosquitoes can then transmit West Nile virus to humans and animals while biting to take blood. The virus is located in the mosquito's salivary glands. During blood feeding, the virus may be injected into the animal or human, where it may multiply, possibly causing illness.

Q. If I live in an area where birds or mosquitoes with West Nile virus have been reported and a mosquito bites me, am I likely to get sick?
A. No. Even in areas where the virus is circulating, very few mosquitoes are infected with the virus. Even if the mosquito is infected, less than 1% of people who get bitten and become infected will get severely ill. The chances you will become severely ill from any one mosquito bite are extremely small.

Q. Can you get West Nile encephalitis from another person?
A. No. West Nile encephalitis is NOT transmitted from person-to-person. For example, you cannot get West Nile virus from touching or kissing a person who has the disease, or from a health care worker who has treated someone with the disease.

Q. Is a woman's pregnancy at risk if she gets infected with West Nile virus?
A. There is one documented case of transplacental (mother-to-child) transmission of WNV in a human. Although the newborn in this case was infected with WNV at birth and had severe medical problems, it is unknown whether the WNV infection itself caused these problems or whether they were coincidental. More research will be needed to improve our understanding of the relationship - if any - between WNV infection and adverse birth outcomes.

Nevertheless, pregnant women should take precautions to reduce their risk for WNV and other arboviral infections by avoiding mosquitoes, using protective clothing, and using repellents containing DEET (See Using Repellent Safely). When WNV transmission is occurring in an area, pregnant women who become ill should see their health care provider, and those whose illness is consistent with acure WNV infection, should undergo appropriate diagnostic testing.

Q. Besides mosquitoes, can you get West Nile virus directly from other insects or ticks?
A. Infected mosquitoes are the primary source for West Nile virus. Although ticks infected with West Nile virus have been found in Asia and Africa, their role in the transmission and maintenance of the virus is uncertain. However, there is no information to suggest that ticks played any role in the cases identified in the United States.

Q. How many types of animals have been found to be infected with West Nile virus?
A. Although the vast majority of infections have been identified in birds, WN virus has been shown to infect horses, cats, bats, chipmunks, skunks, squirrels, and domestic rabbits.

Q. Can you get West Nile virus directly from birds?
A. There is no evidence that a person can get the virus from handling live or dead infected birds. However, persons should avoid bare-handed contact when handling any dead animals and use gloves or double plastic bags to place the carcass in a garbage can.

Q. Can you get infected with West Nile virus by caring for an infected horse?
A. West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person or animal-to-person transmission of West Nile virus. Normal veterinary infection control precautions should be followed when caring for a horse suspected to have this or any viral infection.

Q. Can you get WNV from eating game birds or animals that have been infected?
A. There is no evidence that WNV virus can be transmitted to humans through consuming infected birds or animals. In keeping with overall public health practice, and due to the risk of known food-borne pathogens, people should always follow procedures for fully cooking meat from either birds or mammals.

Q. How does West Nile virus actually cause severe illness and death in humans?
A. Following transmission by an infected mosquito, West Nile virus multiplies in the person's blood system and crosses the blood-brain barrier to reach the brain. The virus interferes with normal central nervous system functioning and causes inflammation of brain tissue.

Q. How long does the West Nile virus remain in a person’s body after they are infected?
A. There is no scientific evidence indicating that people can be chronically infected with West Nile virus. What remain in a person’s body for long periods of time are antibodies and “memory” white blood cells (T-lymphocytes) that the body produces to the virus. These antibodies and T-lymphocytes last for years, and may last for the rest of a person’s life. Antibodies are what many diagnostic tests look for when clinical laboratories testing is performed. Both antibodies and “memory” T-lymphocytes provide future protection from the virus.

Q. If a person contracts West Nile virus, does that person develop a natural immunity to future infection by the virus?
A. It is assumed that immunity will be lifelong; however, it may wane in later years.

VII. Blood Transfusion, Organ Donation and Blood Donation Screening Information

Publications concerning WNV and blood donations/transfusion-associated cases:

Q. What is being done to reduce the risk of transfusion-related West Nile virus transmission?
A.All blood banks in the United States have been screening blood donors and donations for West Nile virus since 2003.

State and local public health departments report cases of West Nile virus infection in patients who have received blood transfusions during the 4 weeks before they got sick to the blood collection agency that collected the donation. Health departments also report this information to CDC through ArboNET, the national database where information about cases of West Nile virus is kept. In addition, cases of West Nile virus infection in people who donated blood in the 2 weeks preceding illness onset should also be reported to CDC and blood collection agencies where the sick person donated blood. The blood collection agencies destroy potentially infectious units of blood.

A. The blood screening methods allow blood banks to destroy potentially infectious blood before it is given to anyone.

In addition, public health departments and blood banks cooperate to identify and destroy blood products (if necessary) from donors who develop a West Nile viral illness after they give blood. If someone becomes ill after a transfusion, blood banks destroy the blood products taken from the donor of the transfused blood. Prompt reporting of these cases helps facilitate withdrawal of potentially infected blood components.

Q. Should people avoid donating blood?
A. No. There is no risk of of being infected by West Nile virus through giving blood. Blood saves lives and is always needed, especially during the summer months. Because donating blood is safe, we encourage blood donation now and in the future. We also encourage all donors to truthfully answer the questions asked by the blood bank to make sure they are fit to donate on a given day.

Q. Should people avoid getting blood transfusions or organ transplants?
A. No. About 4.5 million people receive blood or blood products annually. The benefits of receiving needed transfusions or transplants outweigh the potential risk for West Nile virus infection. However, doctors and their patients who need blood transfusions or organ transplants should be aware of the risk for West Nile virus infection.

Q. If a person had a West Nile virus infection in the past, can they still donate blood?
A. Yes. West Nile virus infections do not last very long. The virus is in the blood for a very short time. People fight the virus and usually get rid of it in a few days. To get rid of the virus, they develop antibodies against it. Antibodies keep people from getting a West Nile virus infection again.

People who have been diagnosed with West Nile virus confirmed by positive laboratory testing should not be allowed to donate blood for 120 days from the start of their symptoms or their laboratory diagnosis, whichever is later. If there are no symptoms to suggest a West Nile virus illness, a positive West Nile virus antibody test result alone should not be grounds for refusing a blood donation.

Q. If I recently had a transfusion or transplant, should I be concerned about getting West Nile virus?
A. You should be aware of the potential risk for West Nile virus infection and the need to monitor your health. If you have symptoms of West Nile virus or other concerns you should contact your physician. If a patient who recently received a blood transfusion or organ transplantation develops a West Nile virus infection, that does not necessarily mean that the transfusion/transplantation was the source of infection.

Q. What happens to the blood collected from donors that test positive for WNV?
A. When a unit of blood is identified as possibly infected with WNV by initial screening, it is removed from the blood supply. If the confirmation process reveals that the unit is NOT actually infected, the remaining blood products may be used.

Q. Is there enough blood to meet the needs of hospitals?
A. Although there is always an increased demand for blood products during summer months, only a relatively few units of blood will be removed from the blood supply.

Blood donations usually decrease in summer. Despite the recently identified problems with receiving infectious blood, it is still safe to donate blood. CDC encourages people who can donate to consider making a donation during summer months to help ensure adequate blood supplies for all who need them.

Q. If someone who is donating blood at the same time that I do tests positive for WNV, can I catch it from them?
A. No. WNV is generally transmitted through the bite of an infected mosquito. You cannot get infected with WNV from contact with an infected person. For more information, see the Transmission page.

Q. If a blood bank does not use my blood because it tests positive for WNV, does this mean I'm going to get sick?
A. Probably not. What this means is that you have WNV in your blood, so you have been recently bitten by an infected mosquito. Most infected people do not become ill at all and only a very small number develop West Nile fever or more serious disease. It is thought that you will have immunity from WNV for a long period after becoming infected, possibly for life. For more information, visit the Transmission page.

Q. Will the blood bank notify me if my blood tests positive for WNV?
A. Blood banks will contact donors who may have a WNV infection. A subsequent blood sample will be requested in order to help confirm the infection. We thank you in advance for your cooperation in protecting the national blood supply, and helping to validate the tests that are being used.

Q. What do I need to do if my blood tests positive for WNV?
A. If you learn from a blood bank that your blood was likely infected with WNV you may be requested to give another blood sample to help confirm the infection.

Most WNV infections do not cause any symptoms, and do not require any medical attention. There is nothing in particular that you need to do because of the infection. It is also likely that you have antibodies to prevent you from getting sick with WNV in the future. If you were infected with WNV, this does tell you that there is a risk of infection in your area, and it is important for the rest of your family to protect themselves from mosquito bites.

Q. What kind of test is used to test donated blood?
A. During the 2002 WNV epidemic, the blood-banking industry, FDA, and CDC worked together closely to identify WNV transmission to humans through blood transfusion and organ donation. These screening tests identify whether West Nile virus is present in the blood. The tests being used for the blood supply are still being validated by all the agencies involved.
If the test is positive, the blood from this donation is removed from the blood supply. To validate these new tests, further testing is done. In some cases, the screening test result may be a "false positive", and blood banks are taking a cautious approach to avoid future WNV transmission by transfusion. For more information, consult the FDA WNV Web page at http://www.fda.gov/oc/opacom/hottopics/westnile.html.
These blood-screening tests are different than the already validated tests that are used to diagnose WNV infections among ill people who are not donors. Among people who are not donors, we use tests that identify antibodies (proteins in the blood that help fight infection) that are produced by the body in response to a WNV infection.

Q. Can I get tested for WNV at my doctor's office with the blood test that blood banks are using?
A. No. The tests being used at blood banks are new and not licensed by the FDA for routine screening purposes. These tests are being used only at blood banks. If your health care provider suspects you may have WNV illness he/she can send a sample of your blood to a private laboratory or to the state health department for testing for antibodies.

Q. Are all U.S. blood centers testing the blood they collect for WNV?
A. Yes. Screening is going on in every U.S. civilian blood center, including Alaska and Hawaii and Puerto Rico.

Guidance related to donated organs, and the use of screening and diagnostic tests for West Nile virus was issued January 9, 2004 and is posted on the website of the Organ Procurement and Transplantation Network.

The most recent information on West Nile Virus Screening of Blood Donations and Transfusion-Associated Transmission is found in the update of the MMWR Dispatch April 9, 2004.

Also, Detection of West Nile Virus in Blood Donations -- United States, 2003 is found in the MMWR Dispatch September 18, 2003.