"For several years, we had followed smaller groups of patients and felt that many had died prematurely."
PIC: (Credit: AFP/Getty Images)
West Nile virus may be three times more deadly than previously thought, because many deaths associated with the mosquito-borne virus occur years after the initial infection, researchers have said.
The findings were based on a study of 4,144 people in Texas, and were presented at the 2016 Meeting of the American Society of Tropical Medicine and Hygiene (ASTMH) in Atlanta, Georgia.
Among this group of people who became ill with West Nile virus between 2002 and 2012, 286 people died in the first three months.
Another 268 people who survived the initial infection died over the next decade due to complications associated with the virus, researchers found.
"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 lead author Kristy Murray of Baylor College of Medicine and Texas Children's Hospital.
The Texas study showed a 13 percent fatality rate.
Nationwide, about four percent of people are believed to die of West Nile in the acute phase of the illness, or in the first three months, according to the US Centers for Disease Control and Prevention.
The virus causes no symptoms at all in up to 80 percent of people. Some people report fever, rash, body pain, headache, vomiting or diarrhea.
In rare cases, brain swelling and neurologic infections can occur.
Researchers said the delayed deaths in the Texas study were more common among patients who had suffered significant neurological complications early on.
Also, kidney disease was a statistically significant cause of delayed death.
Murray said the study shows West Nile virus can cause health problems years after the initial infection.
"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."
The causes of death came from the Texas state death registry. Researchers also had access to medical records that showed the progress of patients post-infection.
West Nile virus was introduced into the United States in 1999, and from the same family of viruses as yellow fever and Zika, which can cause microcephaly in infants.
"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 and that US federal investments are warranted in finding better ways to treat and prevent it."