Thread: West Nile Virus: What You Need To Know

West Nile Virus: What You Need To Know

Definition

West Nile virus is transmitted by mosquitoes. If you become infected with West Nile virus, you may not experience any signs or symptoms or you may only experience minor ones such as a skin rash and headache. However, some people who become infected with West Nile virus develop a life-threatening illness that includes inflammation of the brain.

West Nile virus is common in areas such as Africa, West Asia and the Middle East. It first appeared in the United States in the summer of 1999 and since then has been found in all 48 contiguous states.

Exposure to mosquitoes where West Nile virus exists increases your risk of getting West Nile virus. Protecting yourself from such exposure, such as by using mosquito repellent and wearing clothing that covers your skin, can reduce your risk.

Symptoms

Most have no symptoms

Most people infected with the West Nile virus have no signs or symptoms.
Mild infection signs and symptoms

About 20 percent of people develop a mild infection called West Nile fever.

Common signs and symptoms of West Nile fever include:
• Skin rash
• Headache
• Fever
• Diarrhea
• Nausea
• Vomiting
• Backache
• Muscle aches
• Lack of appetite
• Swollen lymph glands

Serious infection signs and symptoms

In less than 1 percent of infected people, the virus causes a serious neurological infection. Such infection may include inflammation of the brain (encephalitis) or of the brain and surrounding membranes (meningoencephalitis). Serious infection may also include infection and inflammation of the membranes surrounding the brain and spinal cord (meningitis), inflammation of the spinal cord (West Nile poliomyelitis) and acute flaccid paralysis — a sudden weakness in your arms, legs or breathing muscles.

Signs and symptoms of these diseases include:

• High fever
• Severe headache
• Stiff neck
• Disorientation or confusion
• Stupor or coma
• Tremors or muscle jerking
• Signs and symptoms similar to Parkinson's disease
• Lack of coordination
• Convulsions
• Pain
• Partial paralysis or sudden weakness

Symptoms of West Nile fever usually last three to six days, but symptoms of encephalitis or meningitis can linger for weeks, and certain neurological effects, such as muscle weakness, may be permanent.

Causes

West Nile virus transmission cycle

When a mosquito bites an infected bird, the virus enters the mosquito's bloodstream and eventually moves into the salivary glands. When an infected mosquito bites an animal or a human, the virus is passed into the host's bloodstream, where it may cause serious illness. Birds are the main animal reservoirs for the virus, and the mosquitoes are the transmitters (vectors). Humans and other animals don't pass the virus on to other humans or animals.

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Study in mice identifies molecular target for treatment of West Nile encephalitis

Critical mechanism enables blood-borne immune cells to sense West Nile virus and to neutralize and clear infection in the brain

LOS ANGELES (Jan. 29, 2009 – EMBARGOED UNTIL FEB. 5, 2009 AT NOON EST) – In animal studies, researchers at Cedars-Sinai Medical Center and Yale University have identified molecular interactions that govern the immune system's ability to defend the brain against West Nile virus, offering the possibility that drug therapies could be developed to improve success in treating West Nile and other viral forms of encephalitis, a brain inflammation illness that strikes healthy adults and the elderly and immunocompromised.

In a series of laboratory experiments and studies in mice, the research team found that a specific molecule and "signaling pathway" are critical in detecting West Nile virus and recruiting specialized immune cells that home to and clear infected cells. In mice genetically engineered to lack this molecular pathway, immune cells were detected at a distance but they did not home to brain cells infected by the virus, according to an article published online Feb. 5 in the Cell Press journal Immunity.

The key molecule in this process is Toll-like receptor 7, part of the innate immune system that recognizes pathogens entering the body and activates immune cell responses. Effective signaling is dependent on interleukin 23, a protein that stimulates an inflammatory response against infection. In West Nile encephalitis, according to these studies, Toll-like receptor 7 enables macrophages – immune system cells circulating in the blood – to sense the brain-penetrating virus. These macrophages then respond to interleukin 23 produced in the brain. This brain signal in turn promotes their infiltration and homing from the blood into the brain, where they neutralize and clear the virus.

Transmitted to humans by mosquitoes, West Nile virus is the most common cause of epidemic viral encephalitis in North America and has become a worldwide public health concern. While most healthy people who contract the virus have few if any symptoms, an infection can result in life-threatening brain disease – particularly in the elderly and those with compromised immune systems.

"There is no approved therapy for West Nile encephalitis in humans, in part because the mechanisms of the immune response to the virus are not completely understood. Our results suggest that drug therapy aimed at promoting this signaling pathway may enhance the immune response and thereby promote clearance of this potentially deadly virus," said Terrence Town, Ph.D., one of the article's lead authors and a research scientist at Cedars-Sinai's Maxine Dunitz Neurosurgical Institute. Town is an associate professor in the Department of Neurosurgery and the Department of Biomedical Sciences at Cedars-Sinai Medical Center. He holds the Ben Winters Endowed Chair in Regenerative Medicine at Cedars-Sinai.


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