Diseases & Conditions (A-Z)



























West Nile Fever (West Nile Encephalitis) :

West Nile fever

Alternative names
West Nile fever, West Nile virus, WNV, West Nile Encephalitis, West Nile fever virus,

What is West Nile fever?

West Nile fever is a mosquito-borne infection by the West Nile virus.
West Nile virus (WNV) is a neurotropic virus that produces damage of varying severity and anatomic predilection.
West Nile fever virus was first found in the blood of a person with a high temperature in Uganda in 1937. Since then the virus has been found to be distributed not only in Africa, but also southern Europe, the Middle East, America and even parts of the Far East.

What is the cause of West Nile virus fever?
Its caused by West Nile virus. West Nile virus is an arbovirus. Viruses that are transmitted from one animal host to the next by insects (arthropods) are known as ‘arboviruses’ (arthropod-borne). Viruses comprise small pieces of genetic material (nucleic acid) whose sole purpose in life is to make more of themselves. Because they don’t have all the ability to do this alone, they have to muscle into ‘host’ cells and borrow bits of their machinery. The host develops an immune response to fight off this invasion and the rest follows as a consequence of this eternal struggle.
West Nile virus is transferred mainly between pigeons and crows by ‘Culex’ mosquitoes. People can get infected from the bite of a mosquito that is infected with the virus. The virus is not transmitted from person to person. There is no evidence that a person can get the virus from handling live or dead infected birds. However, it is still recommended that barehanded contact with dead animals is avoided.

What are the symptoms of West Nile fever?
Most people  (8 out of 10) infected with West Nile virus do not develop any symptoms.
Mild infection signs and symptoms
About 1 in 5 people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with this type of West Nile virus disease recover completely, but fatigue and weakness can last for weeks or months.
Serious infection signs and symptoms
About 1 in 150 people who are infected develop a severe illness affecting the central nervous system such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord).
Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.
Severe illness can occur in people of any age; however, people over 60 years of age are at greater risk. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk.
Recovery from severe illness might take several weeks or months. Some effects to the central nervous system might be permanent.
About 1 out of 10  people who develop severe illness affecting the central nervous system die.
Signs and symptoms of West Nile fever usually last a few days, but signs and symptoms of encephalitis or meningitis can linger for weeks or months. Certain neurological effects, such as muscle weakness, can be permanent.

How is West Nile virus Fever diagnosed?
The diagnosis of West Nile virus infection is confirmed with a blood or cerebrospinal fluid (CSF) test to detect WNV-specific IgM antibodies. A CSF test requires a lumbar puncture (spinal tap) to obtain a specimen. IgM antibodies represent recent infection and are usually detectable during active or recent infection within three to eight days after infection, but a negative test within eight days should still be repeated if WNV infection is truly suspected. Unfortunately, WNV IgM antibodies can persist for three months or more, so the test may be positive from a prior infection, or a positive test may be due to cross-reactivity with antibodies to other flaviviruses. Therefore, a positive WNV IgM antibody must be confirmed by much more specialized testing by CDC.

If you're 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
In some cases, an electroencephalography (EEG) — a procedure that measures your brain's activity — or an MRI scan can help detect brain inflammation.

What is the treatment for West Nile virus?
There is no specific treatment for the cause of West Nile virus encephalitis. Treatment, in most cases, consists of treating the complications of the disease such as high fever and aches, low blood pressure, blood loss, convulsions (fits), or raised pressure within the skull.
Anti-inflammatory medications, intravenous fluids, and intensive medical monitoring may be required in severe cases. In milder cases, over-the-counter (OTC) pain relievers such as ibuprofen (Advil, Motrin) or aspirin may help reduce symptoms of pain and fever. There is no specific antibiotic or antiviral for the viral infection. There is no vaccine to prevent the virus.
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 recover better than those who don't receive the drug, but more study is needed.

Is it possible to prevent West Nile virus infection?
Personal protective measures can be taken to greatly reduce the risk of being bitten by an infected mosquito.
Your best bet for preventing West Nile virus and other mosquito-borne illnesses is to avoid exposure to mosquitoes and eliminate standing water, where mosquitoes breed.
Unclog roof gutters.
Empty unused swimming pools or empty standing water on pool covers.
Change water in birdbaths and pet bowls regularly.
Remove old tires or unused containers that might hold water and serve as a breeding place for mosquitoes.
Install or repair screens on windows and doors.
To reduce your 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 outdoors.
Apply mosquito repellent containing an Environmental Protection Agency-registered insect repellent 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. Follow the directions on the package, paying special attention to recommendations for use on children.

What is the prognosis of West Nile virus infection?
While the general prognosis is favorable, current studies indicate that West Nile Fever can often be more severe than previously recognized, with studies of various recent outbreaks indicating that it may take as long as 60–90 days to recover.

Age and overall health before infection is more predictive of an individual's likelihood of recovery. Those over 65 years of age are more likely to be hospitalized, to be discharged to a residence outside the home, and to have prolonged residual effects. Those under 65 years of age are most likely to have full recovery. Children are least likely to be affected by neuroinvasive disease or prolonged residual symptoms and signs.

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