This post originally appeared in The Wall Street Journal.

Researchers in Texas find 13% of patients there died, some years after infection

ATLANTA—West Nile virus may be deadlier than public health officials and doctors have thought, according to a new study.

The virus, which like Zika is transmitted to humans mostly by mosquitoes, causes a fever and other symptoms in about one out of every five people it infects. While the majority of those infected never develop any symptoms, patients in about 4% of the 43,937 U.S. cases reported to the Centers for Disease Control and Prevention from 1999 to 2015 died.

Yet researchers in Texas discovered a much higher death rate in an analysis of West Nile cases in their state. Of 4,144 patients who were ill from 2002 to 2012, 13% died, they found in their analysis of data, which went through the end of 2013. Nearly half of the deceased were patients who had recovered from their initial illnesses, only to die months or years later of causes related to the virus.

The patients died of kidney failure—the virus replicates in the kidneys—as well as infectious, digestive and circulatory causes. Most had had severe forms of infection, such as encephalitis.

The findings suggest more needs to be done to protect people from West Nile, said Kristy Murray, principal investigator of the study. She is assistant dean of the National School of Tropical Medicine at Baylor College of Medicine and associate vice chair for research at Texas Children’s Hospital in Houston.

“This data backs up our concerns: West Nile not only causes disease but increases mortality,” she said.

The study was presented Monday at the annual meeting of the American Society of Tropical Medicine & Hygiene.

Patients under 60 years old had a risk of dying from kidney disease that was 11 times higher than for the general population of that age group, Dr. Murray said. That difference “is big, really big,” she said.

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