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West Nile virus increases risk for mortality years after infection
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In the largest study to investigate the long-term effects of West Nile virus, researchers found that patients aged younger than 60 years who appeared to have recovered from the virus were 11 times more likely to die several years after infection compared with the general population.
“While we understand the current focus on Zika virus, for many people in the United States today, West Nile virus (WNV) is the much more serious mosquito-borne threat and that threat may persist even for patients who appear to have survived the infection unscathed,” Kristy O. Murray, DVM, PhD, of Baylor College of Medicine and Texas Children’s Hospital, said in a press release.
Murray told Infectious Disease News that she and her colleagues observed a considerable amount of deaths in WNV survivors who were otherwise healthy before infection. After a study conducted by the CDC also indicated there may be an increased risk for death years following WNV infection, the researchers examined the association in a much larger sample size.
The analysis included 4,144 patients in Texas who were infected with WNV between 2002 and 2012. Among them, 286 died primarily from the virus or an unspecified infectious source less than 90 days after infection. However, an additional 268 deaths occurred among patients who seemed to have recovered from the infection. Most delayed deaths (n = 210) occurred in patients with the neuroinvasive form of the disease.
Murray said the median duration between infection onset and delayed mortality was 3 years. The combined fatality rate accounting for both acute and delayed deaths was 13% — which is much higher than the 4% acute fatality rate estimated by the CDC, according to the press release. The main cause of delayed death was kidney disease, which is suspected to be a long-term complication of WNV. During a previous study in 2012, Murray and colleagues found that 40% of 139 patients with WNV developed chronic kidney disease.
“That’s a way higher percentage than what would be expected for the general population,” she said. “This should prompt physicians to monitor the renal health of their patients if they’ve had WNV.”
Because of the large sample size, the researchers are “very confident” in their results, according to Murray. However, almost half of their data are from patients who were infected at the end of the study period and were not followed long after the acute phase of illness.
“They could be minimizing the effect,” she said, “So, [delayed mortality] is probably more than what we’re reporting, but since there’s an 11 times greater risk of death in people who are under age 60, we felt that it was important to get that information out there.”
In releasing these data, Murray hopes it will drive forward research for a WNV vaccine.
“I don’t think people understand how devastating this illness can be,” she said. “Everybody focuses on what the acute death picture is like, but people don’t think about the long-term implications of infection.
“This is a virus that’s never going away. It would be great if we could encourage further [vaccine] development. In 2012 we had our largest outbreak to date, which was over 1,800 cases in Texas alone. Those are 1,800 cases we could have prevented.” – by Stephanie Viguers
Reference:
Murray KO, et al. Abstract 604. Presented at: American Society of Tropical Medicine and Hygiene conference; Nov. 13-17, 2016; Atlanta.
Disclosure: Murray reports no relevant financial disclosures.
Perspective
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Stephen Higgs, PhD
This study reveals that infection with West Nile virus has more significant long-term effects than we realized. Obviously as we get older, our immune systems change, our general health may change and this can have all kinds of consequences, with, for example, latent infections from many years earlier suddenly flaring up. Remember that nobody in the U.S. was infected before 1999 with West Nile virus and so we have no way to know what happens after 20 years.
A better understanding of an infection like this over time is bound to help us understand how to prevent and treat West Nile. These findings will alert physicians to look for tell-tale signs that might indicate declining health due to previous infection with West Nile virus. They may be more likely to ask a patient if they think they have been infected and perhaps run blood tests to look for signs of previous infection.
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