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New West Nile Threat: Kidney Disease

Even Without Symptoms, West Nile Virus May Lead to Lasting Infection of the Kidneys
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West Nile virus arrived in the U.S. in 1999 and spread across the country in 2002-2003. Since then, an estimated 3 million people in the U.S. have been infected.

Even if only 5% ended up with kidney disease -- a much lower percentage than seen in the Murray study -- over time that would mean about 150,000 Americans have persistent infections and are at risk of kidney disease. And more people are being infected every year.

The persistent infection can't spread from person to person, Schaffner says.

"A person with persistent infection is not hazardous in the home or anywhere else," he says. "We get it from mosquitoes, and they get it from birds. In a person it is a dead-end infection and is not going to go anywhere else."

There's no vaccine against West Nile virus. Vaccines do exist for similar viruses spread by mosquitoes, making a West Nile vaccine at least technically possible. Tests of blood and cerebrospinal fluid (CSF) can detect acute infection. Murray says her lab has developed a test to detect virus in the urine.

There's no treatment for West Nile virus infection. Murray says that in animal studies, existing antiviral drugs appear to make the infection worse, not better.

Anyone who has had West Nile in the past should get annual checkups of kidney function, Schaffner and Murray suggest.

The CDC said it would not comment on the work of Murray, a former agency employee, for this story.

Murray and colleagues reported their findings in the online journal PLoS. Since they submitted their results, Murray says her team has confirmed persistent human West Nile infection by directly seeing live virus in urine with an electron microscope, a more sensitive test than she used in the original study.

2012 West Nile Season Beginning, Not Ending

With about 700 reported cases in 43 U.S. states as of the second week of August, the 2012 West Nile season is off to a fast start.

Case counts and deaths have not yet peaked, says infectious disease expert Jorge Parada, MD, MPH, professor of medicine at New Orleans' Loyola University and medical spokesman for the National Pest Management Association.

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