The West Nile virus is an arbovirus (meaning it is spread by mosquitos, ticks, or other arthropods) that can cause infections in animals and humans; in some cases, the infections can lead to fatal meningitis or encephalitis, which are inflammations of the spinal cord and brain. West Nile virus is considered a seasonal epidemic in North America, and it occurs mainly in the summer, but can continue into the fall. In many cases, it can be a serious illness that generally affects the central nervous system, leading to a variety of symptoms that differ from person to person. It is not contagious by touch, but can be spread by infected mosquitoes, transfusions, transplants, or from mother to child during pregnancy.
Description
West Nile virus infections usually begin with flu-like symptoms. Only approximately one in 150 people infected will develop severe symptoms, including headaches, neck stiffness, disorientation, seizures, fever, numbness, paralysis, and/or muscle weakness. In the worst cases, infection with West Nile virus can lead to death or permanent disability. These cases are usually due to either the age of the patient or the health status. Symptoms generally do not occur in healthy individuals.
Demographics
The West Nile virus has been observed mainly in temperate regions of Europe and North America, and has also been discovered to be the cause of human illness in the United States. The first known case in the United States was reported by the New York City Department of Health in late August 1999. Careful surveillance identified 59 patients who were hospitalized in New York City due to West Nile virus infections during August and September 1999. The median age of these patients was 71 years (range is five to 95). As of April 2004, only one case has been reported by the Centers for Disease Control. The West Nile virus has been observed in Africa, the Middle East, and west and central Asia. The first case was discovered in 1937 in an adult woman in the West Nile district of Uganda. The virus was characterized in Egypt during the 1950s.
An infection due to the West Nile virus does not produce symptoms in most people. In fact, only 20% of people who are infected will develop symptoms. Of these, the majority will recover and will not become infected again. The West Nile virus can infect males and females with equal frequency. There is no known predilection for people of specific ethnic backgrounds. People over 50 years old are at the highest risk of having serious illness associated with the infection. There is a very low risk of contracting this illness by medical procedures such as transplantation and blood transfusions. Although pregnancy and breast-feeding do not increase the risk of becoming infected with the virus, the risk to the fetus or nursing infant of an affected mother is currently being investigated. Horses, birds, and other animals have also been shown to be susceptible to viral infection.
Causes and symptoms
When a person is infected with West Nile virus, usually via a mosquito bite from a mosquito harboring the virus, it is unlikely that the individual will develop symptoms. Of the infected individuals that develop symptoms, there are either mild or severe clinical manifestations. The majority of infections are mild.
Characteristics of mild infections include:
mild illness, including fever
fever and symptoms persist no more than six days, usually lasting only three days
symptoms usually develop three to 14 days after exposure, consistent with the incubation period
illness can be sudden and accompanied by anorexia (loss of appetite), nausea, headaches, rash, muscle weakness, vomiting, and/or lymphadenopathy (swollen lymph glands)
Characteristics of severe infections include:
Severe symptoms can result in neurological disease in approximately one in 150 cases, with the elderly at highest risk.
Neurological symptoms include disorientation, seizures, and cranial nerve abnormali>ties.
Symptoms include high fever, weakness, significant alterations in behavior, eye problems, and stomach problems.
In rare cases, flaccid paralysis along with severe muscle weakness can occur.
Illness can be sudden and accompanied by anorexia (loss of appetite), nausea, headaches, rash, muscle weakness, vomiting, and/or lymphadenopathy (swollen lymph glands).
Diagnosis
Diagnosis requires clinical observation by an experienced physician as well as positive results from specific laboratory tests. Factors that assist in the diagnosis are recent travel experiences, the season that the symptoms developed, the age of the patient, and whether there are reports of other cases in the same geographical location that the patient was present during the time of exposure. Patients who have encephalitis, meningitis, or symptoms involving the central nervous system, which could lead a physician to suspect the West Nile virus, can be referred to health departments nationwide or the Centers for Disease Control (CDC) for testing. The CDC has confirmed all human cases.
The diagnostic test involves an assay that detects a virus-specific antibody (IgM) in the cerebral spinal fluid from patients. Blood can also be tested. If this test is negative, it is very unlikely that the infection is due to the West Nile virus; the other clinical explanations such as St. Louis encephalitis (SLE) should be considered. There is also a test that measures SLE virus-specific antibodies. Currently, there is a vaccination for horses, but not for humans.
Laboratory findings include normal to elevated white blood cell numbers with anemia (low red cell numbers). A deficiency of sodium in the blood (hyponatremia), which is usually associated with encephalitis, as well as normal glucose and a general increase in proteins can all be observed. A magnetic resonance imaging (MRI) scan can also be helpful, if specific areas of the brain show an abnormality, including the leptomeninges and/or the periventricular areas.
Treatment team
The treatment team might consist of the physician who initially sees the patient, usually a general practitioner, an infectious disease specialist, and neurologist. In severe cases, a complete medical team consisting of emergency room physicians and staff, nurses, and officers from the CDC might be necessary. Due to the risk of an epidemic, it is important for physicians to report these types of infections to the local health department.
Treatment
There is no cure for West Nile virus infection once the infection occurs. Treatment, therefore, is supportive and palliative. In the more severe cases, recurrent hospitalizations may necessitate life support services. The primary treatment is focused on lessening the symptoms and preventing secondary infections, which could include urinary tract infections and pneumonia in patients that develop severe illness. Intravenous fluids can be helpful during hospitalizations, along with airway management and good nursing care.
Recovery and rehabilitation
Most patients who develop symptoms recover from West Nile virus infections. The symptoms can be no worse than getting the flu. However, older patients and patients with health-related problems (particularly those that affect the immune system) have more difficulty recovering.
Clinical trials
The Warren G. Magnuson Clinical Center is currently recruiting participants for a clinical trial on the West Nile virus. The Patient Recruitment and Public Liaison Office's e-mail address is prpl@mail.cc.nih.gov.
The National Institutes of Health is conducting phase II clinical trials to investigate whether an experimental drug, Omr-IgG-am™IV, is a safe and effective treatment for West Nile virus-induced infections. This drug contains antibodies that help fight infection and is designed to target the West Nile virus. Another study by the same center has also been initiated to investigate the natural history of infection in patients with, or at risk of developing, West Nile virus-specific encephalitis or myelitis.
A third clinical trial sponsored by the National Institute of Allergy and Infectious Diseases (NIAID) in phase I and II is to test the tolerability of Omr-IgG-am, its efficacy as a vaccine, and its effectiveness in reducing morbidity and mortality (disability and death) in patients with a confirmed diagnosis of the West Nile virus disease. The contact is Walla Dempsey; the e-mail is wdempsey@niaid.nih.gov.
Finally, a clinical trial is ongoing to identify healthy individuals who might be eligible for a phase I vaccine clinical trial sponsored by the Vaccine Research Center at the National Institutes of Health. The Patient Recruitment and Public Liaison Office's e-mail address is prpl@mail.cc.nih.gov.
High doses of a drug called Ribavirin and another called interferon alpha-2b were found to be effective in research studies, but currently no controlled clinical trials in humans have been initiated for these or other types of medications in the therapeutic management of West Nile virus infections and encephalitis.
Prognosis
The prognosis for persons with West Nile virus infection is quite favorable in patients that are young and in otherwise good health. Older persons and patients with health complications can have a poorer prognosis. In rare cases, death is possible.
Special concerns
It is important to contact the local health department when finding dead birds or other animals that die suddenly of an unknown cause during suspected or confirmed local outbreaks of West Nile virus. Health officials monitor mosquito and bird populations to determine local risk for West Nile virus activity.
A person's exposure to mosquitoes and other insects that harbor arboviruses can be reduced by taking precautions when in a mosquito-prone area. Insect repellents containing DEET provide effective temporary protection from mosquito bites. Long sleeves and pants should be worn when outside during the evening hours of peak mosquito activity. When camping outside, intact mosquito netting over sleeping areas reduces the risk of mosquito bites. Communities also employ large-scale spraying of pesticides to reduce the population of mosquitoes, and encourage citizens to eliminate all standing water sources such as in bird baths, flower pots, and tires stored outside to eliminate possible breeding grounds for mosquitoes.
BOOKS
Despommier, Dickson. West Nile Story. New York: Apple Trees Productions, 2001.
White, Dennis J., and Dale L. Morse. West Nile Virus: Detection, Surveillance, and Control. New York: New York Academy of Sciences, 2002.
PERIODICALS
Nash, D., et al. "The Outbreak of West Nile Virus Infection in the New York City Area in 1999." New England Journal of Medicine 344, no. 24 (June 14, 2001): 1807–14.
Centers for Disease Control and Prevention (CDC) Division of Vector-Borne Infectious Diseases. P.O. Box 2087, Fort Collins, CO 80522. (800) 311-3435. dvbid@cdc.gov. <http://www.cdc.gov/ncidod/dvbid/index.htm>.
