The majority of WNV infections will manifest asymptomatically. West Nile fever offers an excellent prognosis associated with quick recovery and no adverse side-effects. The majority of symptoms will resolve within a few days or weeks of manifestation. However, the prognosis is not a positive for patients suffering the more severe syndromes attributable to WNV infection. Symptoms of West Nile encephalitis, West Nile meningitis, and West Nile meningoencephalitis can last for several weeks, as well as cause severe and permanent neurological damage.
Inflammation can interfere with the brain and central nervous system and result in death, especially amongst the elderly population. Patients with West Nile poliomyelitis may suffer prolonged muscle weakness and loss of motor control. Long-term rehabilitation is typically required and a full recovery is not assured. If the poliomyelitis affects muscles used for breathing, death from respiratory failure may result. Although there is a vaccine used for horses and exotic birds in zoos, there is no WNV vaccine for humans at the current time. Several pharmaceutical companies, however, have WNV vaccines in development.
Prevention techniques of WNV typically coincide with avoidance measures against mosquito bites; the primary source of the virus. While camping outdoors, knockdown spray or bed netting with pyrethrum is suggested. Mosquito eradication programs have been instituted in most major cities. Public health authorities can utilize United States Environmental Protection Agency -approved "adulticidies" in areas suspected of the presence of WNV. The Culex pipiens mosquito is the primary vector of WNV transmission and is also commonly live and feed in urban areas. Special precautions should be taken to reduce exposure to these potentially infected insects.
Screen doors and enclosed porches can help keep mosquitoes from coming into the house. It should be noted that studies have shown that mosquito control devices such as "bug zappers" and CO2-baited traps do not significantly reduce the risk of being bitten. Removing potential mosquito breeding areas from near the home and from the neighbourhood can further reduce the risk of bites. Any container which can collect half an inch of standing water can become a potential breeding site in as little as five days. Old tires, empty plant pots, and empty trashcans should be removed, while water sources like ponds or birdbaths should be cleaned regularly.
Standing water on any property should be drained, such as from clogged eves.
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Swimming pools and hot tubs should be properly covered and chlorinated to prevent mosquitoes breeding in them. Mackenzie J. Barrett, and V. Deubel eds. Japanese encephalitis and West Nile viruses Berlin : Springer, O'Leary D. Marfin, S. Montgomery, A. Kipp, J.
Lehman, B. Biggerstaff, et al. Peterson L, and J. Rappole J. Derrickson, and Z. Huhn G', J. Sejvar, S. Montgomery, and M. Centers for Disease Control and Prevention. Flavivirus — An arbovirus that can cause potentially serious diseases, such as dengue, yellow fever , Japanese encaphilitis, and West Nile fever. Weakness, tingling, and abnormal sensations in the arms and upper body can progress until the muscles become totally disabled and the patient is effectively paralyzed.
Meninges — A series of membranous layers of connective tissue that protect the central nervous system brain and spinal cord. Damage or infection to the meninges, such as in meningitis, can cause serious neurological damage and even death. Zoonotic diseases — Diseases caused by infectious agents that can be transmitted between or are shared by animals and humans. This can include transmission through the bite of an insect, such as a mosquito.
Cite this article Pick a style below, and copy the text for your bibliography. September 22, Retrieved September 22, from Encyclopedia. Then, copy and paste the text into your bibliography or works cited list. Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia. 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.
West Nile virus infections usually begin with flu-like symptoms. 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. 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.
Careful surveillance identified 59 patients who were hospitalized in New York City due to West Nile virus infections during August and September The median age of these patients was 71 years range is five to As of April , only one case has been reported by the Centers for Disease Control. The first case was discovered in in an adult woman in the West Nile district of Uganda. The virus was characterized in Egypt during the s.
An infection due to the West Nile virus does not produce symptoms in most people. Of these, the majority will recover and will not become infected again.
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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. 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.
Origin and evolution of Japanese encephalitis virus in southeast Asia.
Of the infected individuals that develop symptoms, there are either mild or severe clinical manifestations. The majority of infections are mild. Characteristics of severe infections include:. 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.
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.
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.
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. The Warren G. Magnuson Clinical Center is currently recruiting participants for a clinical trial on the West Nile virus. 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. 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.
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. 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. 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.
Despommier, Dickson. West Nile Story. New York : Apple Trees Productions, White, Dennis J. Nash, D. Bren, Linda. Food and Drug Administration. May 1, June 3, Box , Fort Collins , CO The West Nile virus is a member of the family Flaviviridae, a virus that has become more prominent in Europe and North America in the past decade. The virus, which is closely related to the St. Louis encephalitis virus found in the United States , causes an encephalitis swelling of the brain in domestic animals such as horses, dogs, cats , wild animals, and wild birds.
How do they attack the body?
When transferred from an infected animal to a human, the viral infection can produce encephalitis as well as inflammation of nerve cells of the spinal cord meningitis. In , the virus was isolated from a woman in the West Nile District of Uganda. This locale was the basis for the designation of the virus as the West Nile virus. During the s, the ability of the virus to cause the serious and life-threatening human disease was recognized.
In the s, the virus was established as a cause of equine encephalitis.
Figure 3 from Recent advances in Japanese encephalitis - Semantic Scholar
Whether the virus has spread geographically from Uganda, or whether increased surveillance has detected the virus in hitherto unsuspected regions is not clear. However, the pattern of detection has been that of a global dissemination. The virus has come to prominent attention in North America following its appearance on the continent. That year, 62 cases of the disease were reported in New York City. Seven people died. The following year 21 more cases occurred, and two of the people died. In and , the West Nile virus was confined to the northeastern coastal states of the United States.
However, an inexorable spread to other regions of the country and the continent has begun. In the summer of , dead birds that tested positive for the virus were found as far north as Toronto , Canada , as far south as the northern portion of Florida , and as far west as Milwaukee , Wisconsin.
Scientists anticipate that the virus will continue to disseminate. During the summer of , more than cases and at least 14 deaths were reported — with a continued spread of the virus into the western United States. By August , West Nile virus was reported in 41 states. The mosquitoes are the prime vector of the West Nile virus. When mosquitoes obtain a blood meal from an infected animal or a bird, they acquire the virus. The virus resides in the salivary glands of the mosquito, to be passed on to a human when the mosquito seeks another blood meal.
The cases in New York City, especially those in , are thought to have been caused by the bite of virus-infected mosquitoes that survived the cold winter months. The emergence of the mosquito in the spring can facilitate the re-emergence of the virus. For example in North America, there were large die-offs of crow populations due to West Nile virus in the Spring of and then again in the Spring of Upon entry to a host's bloodstream, multiplication of the virus in the blood occurs.
Then, by a mechanism that is not yet deciphered, the virus crosses the barrier between the blood and the brain. Subsequent multiplication of the virus in brain tissue causes nervous system malfunction and inflammation of the infected brain tissue. Although a large population of mosquitoes may be present, the chances of acquiring West Nile virus via a mosquito bite is small. Data from the examination of mosquito populations indicates that less than one percent of mosquitoes carry the virus, even in areas where the virus is known to be present. The mosquito to human route of infection is the only route known thus far.
The virus is known to infect certain species of ticks. However, as of early , tick-borne out-break of the disease has not been documented in humans. Person to person contact cannot occur. Even exchange of body fluids between an infected human and an uninfected person will not transmit the virus. Currently no human vaccine to the West Nile virus exists. Prevention of infection consists of repelling mosquitoes by conventional means, such as the use of repellent sprays or creams, protective clothing, and avoiding locations or times of the day or season when mosquitoes might typically be encountered.
West Nile virus, microorganism and the infection resulting from it, which typically produces no symptoms or a flulike condition. The virus is a flavivirus and is related to a number of viruses that cause encephalitis. It usually is transmitted through the bite of several mosquito species, and can infect humans and more than animal species, including alligators, horses, and many common birds. A number of North American bird species, including the blue jay , crow, and house sparrow, act as reservoirs of the virus.
About one fifth of humans infected with the virus develop West Nile fever, which in most people is characterized by fever, headache, muscle ache, joint pain, nausea and vomiting, and in some cases rash and swollen lymph nodes swollen glands. Loss of vision, tremors and convulsions, paralysis, coma, and, in some cases, death may result.
Older persons and persons with a weakened immune system are most susceptible to severe cases of the disease, and they may suffer from longer-term effects including weakness and fatigue, headaches, memory loss and confusion, and depression. There is no treatment or vaccine for the virus except to alleviate the symptoms; controlling the mosquitoes that carry the disease is the most effective way to limit its spread.
West Nile virus was first identified in in the West Nile district of Uganda. It was subsequently found in much of the rest of Africa, the Middle East , and warmer regions of Asia and Europe. Its first recorded appearance in the United States was in Queens, N. West Nile fever is a viral infection that can result in inflammation of the brain, called encephalitis en-seh-fuh-LYE-tis.
The virus that causes it is spread to humans by infected mosquitoes. Most of the time, people with WNF become only mildly ill. In some cases, however, WNF can develop into a life-threatening disease. If the virus passes into the brain, the infection can cause serious inflammation and complications affecting the nervous system.
Of those infected, people older than 50 have the greatest risk of developing severe disease. It was not found in the Western Hemisphere until , when the first case appeared in the United States. Since then, presence of the virus has been documented in 39 states and the District of Columbia. WNF tends to occur more often in the summer and early fall, but the vast majority of cases likely go unreported because they cause only mild illness, if any.
Generally, a person cannot contract WNF from another infected person or from an infected animal transmission of the virus through a blood transfusion has been confirmed in some cases. Likewise, infected people cannot spread the virus to animals. Scientists think that the virus is transmitted almost exclusively by the bite of an infected mosquito. The chances of becoming ill with WNF actually are very small. Of all the mosquitoes in any area where infected mosquitoes have been found, fewer than 1 percent carry the virus. The transmission cycle begins when a mosquito bites an infected bird and takes in blood that contains WNV.
If the mosquito then bites a human, it can transmit the virus to that person. There is no evidence that humans can contract the disease by handling live or dead birds or any other animal that has been infected with the virus. Still, it is never a good idea to handle dead animals with bare hands; experts recommend that people always use disposable gloves and place the dead animal in a plastic bag when disposing of it.
Very severe cases can result in death, but this is rare. Symptoms usually begin 3 to 15 days after infection. If WNF is suspected, the first thing a doctor will do is take a history, which means asking a person about prior health, when symptoms began,. In the summer of , dead birds began appearing all over the New York metropolitan area. References Publications referenced by this paper. Japanese encephalitis. A double-blind placebocontrolled trial of interferon alpha in Japanese encephalitis.
A poliomyelitis-like syndrome from West Nile virus infection. Arturo Leis , Dobrivoje S. Clinical proof of principle for ChimeriVax: recombinant live, attenuated vaccines against flavivirus infections.
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