West Nile Virus Cases Pop Up in Another US State

After getting off to an early start, West Nile virus (WNV) activity is continuing across the United States, as a new study explores how a chemical pathway in brain cells may help prevent the neurological disease caused by the virus.

In 2016, the United States saw 2038 human cases of WNV, with California reporting 424 and Texas reporting 353 of those infections, the highest activity reported in any state. Other states with high activity last year included Colorado with 149 cases, Illinois with 153 cases, and South Dakota with 151 cases. Although most people who become infected with WNV do not typically develop symptoms, the infections can become dangerous when they result in serious neurological illnesses, which can have lasting effects. Of the 2038 human cases reported in the United States in 2016, there were 1140 cases of neuroinvasive disease and 94 of these resulted in death.

Already this year (2017), California and Texas are reporting early WNV activity, with the virus appearing in mosquitoes, birds, and humans. Through continued surveillance efforts, California’s Department of Public Health has recently detected the virus in 3 new mosquito samples from San Bernardino and Tulare counties, and discovered a fourth dead bird in the state testing positive for West Nile. In Texas, the city of El Paso recently reported its first human case of the virus this season, which involved an area man in his 40s who had not recently travelled outside of the area.

In addition to those cases, Nevada’s Clark County is reporting the first human case of WNV of the season for both the county and state. According to the Southern Nevada Health District, the case involves a male over the age of 50, who developed a more serious neuroinvasive form of the virus. Clark County has been tracking WNV since first reporting local mosquitoes had tested positive for the virus in 2004.

“Mosquito bites and the diseases spread by infected mosquitoes are preventable,” said the district’s chief health officer Joe Iser, MD, MSc, in a recent press release. “Southern Nevada residents can take preventive measures against mosquito bites and simple steps to eliminate mosquito breeding sources around their homes to protect themselves, their families, and communities.”

In related news, a recent study published in the journal Cell, details how brain cells defend themselves and fight back in the face of mosquito-borne infections such WNV and others. The study team found that brain cells infected with WNV use a protein called RIPK3 to protect neurons by activating a chemical pathway in brain cells that triggers white blood cells to fight the infection. Although RIPK3 works in cells in other parts of the body to trigger a self-destruct mechanism in the face of infection, this protein works differently in brain cells to help clear WNV from the brain while protecting non-renewable neurons, the authors found.

“RIPK3 acts as part of the milieu of signals that support anti-viral inflammation in the brain,” said the lead author of the paper, Brian Daniels, PhD, in a recent news report on the team’s study. These findings may help health experts understand the mechanism of neurological disease in people infected with WNV and other insect-transmitted viruses, and why some people experience brain damage from the virus while others do not.