Aging Begins at 30

West Nile Virus

Ian Maclean Smith, M.D.
Emeritus Professor
Department of Internal Medicine
University of Iowa Hospitals and Clinics
Creation Date: August 2002
Last Revision Date: August 2002
Peer Review Status: Internally Peer Reviewed

West Nile fever is one of the Arboviruses, a contraction of arthropod (mosquito or a tick) and borne. There are usually sick animals that spread the disease. Most of the viruses are named for the area where they were first recovered, but as a group they are called Flaviviruses because of the prototype yellow fever virus. (Flavius is yellow in Latin.) They are the same size, have the same RNA and the same appearance under the electron microscope.

West Nile virus causes fever and rash (on the second to the fifth day) but rarely affects the brain. It is often only a fever (101 degrees F to 104 degrees F) but with generalized lymph gland and joint involvement. It can be totally without symptoms. When it affects the brain, patients may be disoriented leading to coma. There may also be a stiff neck, convulsions, weakness, paralysis, or abnormal movements. It has to be differentiated from Dengue fever (found in Florida), which is tropical neck and shoulder joint pain with fever.

West Nile virus was first described in the Western Hemisphere in 1999 having been prevalent before that in temperate regions of Africa, the Middle East, the former Soviet Union, western Asia, and parts of Europe. It is common in Egypt and Israel.

In 2002, virus activity is recorded in 33 U.S. states and the District of Columbia (compared to 12 states in 2000). Seven states in 2002 reported human cases for the first time and West Nile virus has now entered the Caribbean. Patients were found in 10 states, mainly New York, New Jersey, Florida and Louisiana.

In 65 reported cases, the patients mean age was 68 (range 9 to 90). The incidence of cases is from 3 per 100,000 under age 60 to 48 per 100,000 at age 70 and above. In addition, there are 300 patients (by blood test) without symptoms for every symptomatic one. Less than 1 in 1,000 infected people die. In the United States there were 149 cases and 18 deaths from 1999 to 2001. In 2002 there have been 112 cases by August 7^th with 5 deaths but only the most obvious cases are reported. Many without symptoms are unreported. There has been dramatic spread west and south from the original focus in New York State to the western borders of states from North Dakota to Texas.

The only other mammals involved have been 735 horses, but they appeared to be dead-end hosts, since the virus doesn't get in the blood in large enough numbers to infect biting mosquitoes. The same is true in humans so they do not pass the disease to others. A vaccine is available for horses. Research is active to produce a human hybrid vaccine by replacing the genes from the envelope of the yellow fever live attenuated vaccine by genes of the West Nile virus.

There is presently no specific treatment. Life support is necessary when encephalitis develops.

For prevention, clothing should protect against mosquitoes. Repellant should be used. Increased Culex mosquito control is essential. Mosquitoes tend to feed (bite) around midnight but they can do so any time. Culex mosquitoes take about 4 blood feedings in their three-week life span. Spraying standing water mosquito reservoirs will reduce the risk. Nonetheless, the virus is here and will continue to spread until all states are involved. There will be focal outbreaks from time to time.

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See related Patient Topics Brain and Nervous System, Dengue, Infections or West Nile Virus.

See related Provider Topics Brain and Nervous System or Infections.

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