West Nile Virus

First isolated in Uganda in 1937, the West Nile Virus was characterized in Egypt in the 1950s. The flavivirus containing RNA first appeared in the United States in 1999 in New York City. The prevalence of the disease has spread across the United States. Epidemiologists noted a westward trend for spreading across the country and by the summer of 2006 the virus had been reported in 48 states.

Monitoring by public health departments included trapping of mosquitoes to determine the size of the mosquito population and classifying the mosquitoes to find West Nile Virus carriers. The also studied sentinel chicken flocks as a predictor for the emergence of the virus, and tested birds for presence of the virus. The practice of setting up and testing sentinel chicken flock was not always a good predictor of the virus’ presence.

West Nile Virus is spread by vector transmission where a living organism passes the virus to the human. The pathogen or cause of disease spends part of its lifecycle in the vector and then completes the rest within the human. The most common vector for West Nile Virus is the Culex tarsalis mosquito.

In addition to contracting West Nile Virus through the bite of a mosquito carrier, transmission through blood transfusion also may occur. After 23 transfu-sion-related infections were reported in the United States in 2002, blood banks around the country began to test potential blood donors for West Nile Virus during warm weather. In 2003, Colorado's state health department declared an end to the West Nile Transmission season on October 1. Thirteen days later, Bonfils Blood Center in Colorado received a positive test revealing the presence of viral genes for West Nile Virus in one donor's blood. This indicated the virus stays in the blood longer than previously believed.

People will develop West Nile symptoms within 314 days of being bitten by an infected mosquito. Symptoms include fever, extreme fatigue, headache, body aches, and occasionally a skin rash and swollen lymph nodes; the illness is similar to a bad case of influenza. Physicians who saw patients with these symptoms advised them to drink plenty of fluids and rest.

If the virus leaves the blood stream and enters the nervous system, a severe form of the illness develops. Meningoencephalitis is an inflammation of the brain and membrane that envelops the brain and spinal cord. Some infected with West Nile Encephalitis have reported continued problems with movement and parasthesia in the limbs for months following the illness. Specific antiviral therapy is not available for the treatment of West Nile Virus nor is a vaccine approved for use in humans, though veterinarians do have a vaccine for use in horses.

In 2005, The National Institute for Allergy and Infectious Diseases began an experimental trial of a gene-based vaccine that doesn't carry live virus; it is composed of a plasmid, a circular piece of DNA. Multiple copies of the plasmid are injected into the muscle with a high-pressure needleless gun, which has been found more effective than traditional needle injection.

Inside the muscle, the body uses the DNA to create the two proteins. The proteins are then released into the bloodstream and the immune system creates antibodies to the proteins to fight the infection. As part of the testing of the vaccine, horses received the vaccine and were later exposed to the virus. The horses did not come down with the West Nile Encephalitis.

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