West Nile Virus Is Off to an Early Start This Season

As several states report their first human cases of West Nile virus of 2017, health officials around the country are urging members of the public to take precautions to help stem the spread of the virus.

West Nile virus (WNV) originated in Uganda, with cases largely confined to parts of Africa, Asia, Europe, and the Middle East until the first case occurred in the United States in 1999 in New York. Believed to be introduced to the United States through an infected mosquito or bird, the virus has since spread across the country via infected mosquitos, with outbreaks occurring each summer. While 70% to 80% of individuals who become infected do not experience any signs of WNV, those who do present with symptoms report having headaches, body aches, joint pains, vomiting, diarrhea, or a rash. Individuals infected with WNV typically recover completely, though symptoms such as fatigue and weakness can persist for weeks. WNV can develop into serious neurological conditions such as encephalitis or meningitis — inflammation in the brain or tissues – for less than 1% of those infected with the virus; in 10% of those with these individuals, serious illnesses may lead to death.

In Tennessee, officials from the Shelby County Department of Health reported the first confirmed human case of WNV of the season in April, and soon after, reported a second case. The infections occurred after local surveillance efforts detected the virus in mosquito pools within 3 of Shelby County’s zip codes. Local vector control efforts have included applying larvicide to bodies of standing water to prevent mosquito breeding. Area news outlets have reported that there were 6 cases of WNV in the entire state of Tennessee in 2016, 2 of which occurred in Shelby County. The Tennessee Department of Health has noted that these cases of the virus have come unusually early this season, and have reminded state residents to use insect repellants, wear products using permethrin (an insecticide), and remove any standing water from their property.

According to Texas’s Department of State Health Services (DSHS), the state has seen its first case of WNV of the season in Montgomery County, just outside of Houston. The infection occurred in late April in a 60-year-old female county resident, who is now in stable condition and recovering at home, according to local news reports. Texas has seen some of the country’s highest case counts of WNV in recent years—in 2016, state health officials reported 370 confirmed human cases and 18 related deaths. High mosquito activity is common in Texas, and officials are reminding state residents to cover exposed skin with long pants and long-sleeved shirts whenever possible, use air conditioning or windows and doors that have functional screens that can keep mosquitoes from getting indoors, and to limit outdoor activities during peak mosquito season.

“Diseases like Zika and West Nile remain threats in Texas, and we need everyone to do their part to protect themselves, their families and their communities,” said DSHS Commissioner John Hellerstedt, MD, in a recent press release. “These are simple steps, and if people take them consistently, they will go a long way toward reducing the number of cases of either disease transmitted in Texas.”

After a wet winter with heavy rains in California, the state’s Department of Public Health (CDPH) has reported its first WNV case of the season in Kings County. In addition, state health surveillance efforts have detected the virus in 3 dead birds, 1 each from San Mateo, Orange, and San Diego counties. In response, the CDPH is asking California residents to stay safe by using insect repellant containing DEET, avoiding outdoor activities during dawn and dusk when mosquitoes are most active, and draining any standing water.