West Nile Virus May Cause Kidney Disease
Posted Aug 24, 2012
The West Nile virus is considered an acute threat, causing death or brain-related disability in a tiny fraction of cases, but a new Houston study suggests it routinely can result in serious, lasting damage.
Baylor College of Medicine researchers studying local people in years after they were infected with the mosquito-borne infection found four in 10 had varying stages of chronic kidney disease related to the virus. The kidney disease is potentially fatal.
"This demonstrates that everybody, not just the elderly and the immune-compromised, needs to take precautions against mosquitoes," said Kristy Murray, a professor of tropical medicine at Baylor College of Medicine and the study's senior author. "Healthy people appear to be quite at risk of kidney disease from bites, too."
Murray said she was very surprised by the study findings -- that West Nile-related kidney disease is occurring, that it's common and that it's even very likely to affect infected people who never had symptoms. She focused on kidney disease after learning about a few study participants' unexpected development of kidney problems.
Because of the study, published online in the journal PLoS, the team is advising doctors to screen patients with any history of West Nile infection for kidney disease and those with unexplained kidney disease for the virus, Murray said. She estimated that roughly 45,000 Houston-area people have been infected with the virus, many of whom don't know it.
Texas is in the midst of its most prolific West Nile season ever, although the greatest numbers by far are occurring in the northern part of the state. Dallas County has confirmed 270 human cases of West Nile disease and 11 deaths this year. Harris County has had 19 cases and three deaths.
Still, Harris County's deaths so far represent the most at this point of the season in recent years. Wednesday night, it conducted aerial spraying of 63,000 acres in the west and north.
Largest outbreak ever?
U.S. health officials said Wednesday that Texas' active season has the nation on pace for the largest outbreak ever. National numbers lag behind the local numbers, but the U.S. Centers for Disease Control and Prevention is reporting 1,118 West Nile illnesses, up from fewer than 700 cases a week ago. The CDC reports 41 deaths.
Only one in 150 infected get severe symptoms from West Nile disease, which can lead to imbalance, coma, paralysis and death. But the conventional wisdom has been that people without symptoms -- eight of 10 of those infected -- and people who recover from mild cases are then immune from the disease.
In her study of 139 Houston-area people infected with the virus and followed for 10 years, however, Murray found that the virus commonly takes residence in the kidney and replicates there, resulting in inflammation and disease as the body tries to fight the infection.
People who survived the disease's most severe symptoms were most likely to have suffered kidney damage -- 60 percent, within seven to nine years after infection -- but a significant percentage of disease occurred in all groups. In those who never had symptoms, 39 percent had kidney disease four to six years later.
Overall, 40 percent of study participants had kidney disease at four to six years and 43 percent had it at seven to nine years.
People who had experienced severe West Nile disease were the most likely to have serious kidney damage.
Chronic kidney disease is divided into five stages. The first two are milder, but stages four and five are usually irreversible and can result in dialysis or transplantation. Conservatively, the estimated 2 million people infected with West Nile nationally could mean an additional 100,000 or more Americans are at some stage of kidney disease.
Though there is no treatment for the West Nile virus, Murray said it is important to catch the kidney disease as early as possible so it can be monitored.
Dr. Lyle Petersen, a CDC West Nile specialist, called Murray's study "intriguing and interesting," but said more work is needed to confirm the findings.
"If true, they are of importance," he added.
Murray, a former CDC official who is also a Texas Children's pediatrician, said the team is continuing to look into the phenomenon and have confirmed the presence of persistent infections by finding the live virus in patients' urine with an electron microscope, a more sensitive test than was used in the study. She said the next step is to understand the relationship between infection and kidney disease.
©2012 the Houston Chronicle
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