by M. Shendrikar MD MPH
What is it?
West Nile Virus (WNV) is a virus that was originally discovered in Uganda, west of the Nile River. It is a common viral illness in Europe, Africa, Asia and Australia. It made its way to the United States in 1999 when the first known cases were documented in New York City. It has since moved its way westward across the US. Cases have been reported in almost all contiguous states, including California.
How is it spread?
WNV is carried by mosquitoes and birds. The only way to transmit WNV is via a mosquito bite. The mosquito must bite a bird that has WNV in order to be infected. Then, that mosquito must bite a human or horse in order to pass the infection along. It is not contagious amongst humans or horses. The only other ways to get WNV is from a blood transfusion (although the blood banks are aware of it and are screening the blood), organ transplantation, via mother to fetus and from breastmilk.
What does it cause?
For the most part, people infected with WNV will develop a flu-like illness between 3 to 10 days after a suspected mosquito bite. Most people will not know that the cause of their “flu” is due to West Nile. Actually, only 1 in 5 people will have symptoms of infection. Symptoms of infection include fever, muscle aches, fatigue, nausea, vomiting, chills, cough, headache, and possibly joint aches. This illness is called West Nile Fever. It may last up to 2 weeks, just like any viral syndrome.
Only 1 in 150 infected people will have severe disease. Those who have severe disease will have persistent fever, headache, neck stiffness, paralysis of their arms or legs, and may not be easily arousable. This is a serious version of the illness and patients should be taken to the hospital to have more tests done. People with severe disease may have an inflammation of the brain and/or spinal cord called encephalitis or meningitis. This illness is called West Nile Encephalitis.