WEST NILE VIRUS MAY BECOME A CHRONIC INFECTION

ovember 10, 2010 (Atlanta, Georgia) — West Nile virus (WNV) might persist for years after acute infection, resulting in long-term neurological consequences in more people than previously thought, a new study suggests.

Kristy Murray, DVM, PhD, from the University of Texas School of Public Health, in Houston, presented the findings here at the American Society of Tropical Medicine and Hygiene 59th Annual Meeting.

"West Nile virus is not just an acute disease," Dr. Murray told Medscape Medical News. "Patients who have the neuroinvasive form of disease will more than likely have long-term symptoms and sequelae," she said. "This is a major finding, considering that more than 1.7 million Americans have been exposed since this virus first came to the United States in 1999," she added.

WNV infection is generally asymptomatic, but a neuroinvasive variant that can result in encephalitis, meningitis, and acute flaccid paralysis occurs in approximately 1 in 150 infected individuals, according to the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.

Dr. Murray and colleagues initially observed that a larger than expected number of patients who presented with WNV infections were experiencing progressive neurological disease or kidney failure. They subsequently investigated long-term outcome in 151 patients with WNV in Houston beginning in 2002.

Of patients who presented with encephalitis, 77% had abnormal neurological findings, and 23% exhibited renal disease (including 5 deaths from renal failure).

Previously, the researchers found that 5 of 25 subjects tested positive for WNV viral particles in the urine. The current analysis indicated that 34 of 81 subjects (42%) had persistent WNV viral shedding in the urine. Of those patients, 65% had proteinuria and 13% developed renal failure.

"People who have been exposed to West Nile virus need to understand that chronic infection is a possibility," Dr. Murray said. "They should be screened for persistence and monitored for kidney disease," she said.

"This is a very interesting finding," noted Robert Tesh, MD, from the University of Texas Medical Branch in Galveston. "People in this cohort have been followed for as long as 7 or 8 years. This is a unique and valuable group that Dr. Murray has collected," he told Medscape Medical News. "Hopefully, the virus can be isolated to strengthen the current findings," he added.

Dr. Tesh pointed out that the abstract states that 1.7 million people are estimated to have been infected, but the CDC estimates now indicate that as many as 3.5 million people in the United States have been infected with WNV since it was first identified in 1999. There is currently no vaccine or treatment for WNV.

The study was not commercially funded. The authors and commentator have disclosed no relevant financial relationships.

American Society of Tropical Medicine and Hygiene (ASTMH) 59th Annual Meeting: Abstract LB-2309. Presented November 6, 2010.