Updated
September 25th, 2019

West Nile Virus in Texas Deadlier Than Zika

New research finds deaths from West Nile Virus reached 13 percent

mosquito

West Nile virus may be much more deadly than previously believed. A recent study found deaths attributable to the mosquito-borne disease occur not just from the immediate infection, but also years later.

During this study’s 10-year period, deaths from West Nile Virus reached 13 percent fatality rate.

The virus replicates in the kidneys, as well as infectious, digestive and circulatory causes. Most cases had severe forms of infection, such as encephalitis.

There is not a specific treatment for West Nile Virus (WNV) infections, nor is there a vaccine to prevent it.

"While we understand the current focus on Zika virus, for many people in the United States today, West Nile virus is the much more serious mosquito-borne threat and that threat may persist even for patients who appear to have survived the infection unscathed," said Kristy O. Murray, DVM, PhD, of Baylor College of Medicine and Texas Children's Hospital, who is the principal author of this study.

Murray and her colleagues looked at 4,144 West Nile virus (WNV) infections that occurred in Texas between 2002 and 2012. The researchers found there were 286 people who died in the acute phase of WNV.

But after examining causes of deaths and symptoms from the initial infection, Murray and her colleagues concluded that 268 people who survived infection subsequently died early (they call it "delayed mortality") due to the virus.

Overall, counting both the acute and delayed group, the researchers attributed 554 deaths to WNV during the 10-year period, a 13 percent fatality rate.

That's much higher than the 4 percent national fatality rate for WNV recorded between 1999 and 2015 by the U.S. Centers for Disease Control and Prevention (CDC),

The CDC statistics accounted only for deaths that occurred during the acute phase of illness.

WNV, which also can infect birds that help spread the virus further, has been detected in all of the lower 48 states since it was introduced into the United States in 1999.

It belongs to the same family of viruses as Zika and yellow fever. Like Zika, most people infected with WNV never experience symptoms. Those who do typically have a fever, nausea, fatigue or a rash.

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In rare cases, it can cause severe neurological complications that can lead to swelling of the brain and spinal cord.

"For several years, we had followed smaller groups of patients and felt that many had died prematurely," Murray said.

"We saw many people who were otherwise healthy until they had West Nile virus--and then their health just went downhill."

Murray said most of the delayed deaths were clustered around a large outbreak of WNV in Texas in 2012. But Murray said other early deaths were recorded up to 10 years after the initial epidemic of West Nile.

She said her research team feels confident in its conclusions because, for each patient, they had access to both information about the course of the initial infection and records maintained by the Texas state death registry that document cause of death.

Murray said that the delayed deaths appeared to be more common in patients who had suffered significant neurological complications during the acute phase of their illness.

Also, for patients suffering delayed deaths, Murray said kidney disease, increasingly suspected as a potential long-term complication of WNV, was statistically found to be a significant cause of death.

Murray was the principal investigator of a 2012 study that followed 139 patients diagnosed with WNV and found 40 percent of them developed chronic kidney disease.

"We had been surprised in the 2012 study to see so much chronic kidney disease develop in younger West Nile patients because it's not that common in people under 60," she said.

"In much the same way that research into Zika virus is showing a more destructive virus than originally thought, we are still discovering previously unreported long-term destructive effects of West Nile," said Stephen Higgs, PhD, president of the American Society of Tropical Medicine and Hygiene.

"Those of us in the tropical medicine community have long been concerned that West Nile is a significant public health problem," said Higgs.