West Nile Season Expected to Continue Into Fall in Some Areas of US

As children go back to school, health officials around the country are reminding the public to continue protecting themselves from mosquitoes, as new cases of West Nile virus activity may continue for several more weeks.

For the week ending September 5, 2017, the Centers for Disease Control and Prevention (CDC) reported that there have been 526 human cases of West Nile virus in 47 states so far in the 2017 season, with only Maine, Alaska, and Hawaii reporting no West Nile activity this year. The total includes 303 cases classified as neuroinvasive and 223 as non-neuroinvasive. Due to the fact that up to 80% of individuals infected with West Nile display no symptoms, those cases go undetected; cases involving febrile illness or severe symptoms are more likely to be reported. Most human infections occur from June through September, although West Nile cases have been reported well into the fall months, as mosquitoes can remain active.

In Alabama, the number of human cases of West Nile so far this season recently rose to 20 as of September 8th, according to new data released by Alabama public health. Following heavy rains from Tropical Storm Irma, the state’s health officials released a statement on September 12th advising the public to be cautious when entering flood-affected areas and to reduce exposure to mosquitoes, as they can carry diseases such as West Nile and Zika virus.

“Residents of flooded areas should be particularly careful to reduce their exposure to mosquito bites,” the statement read. “Many kinds of mosquitoes are most active during the late evening, night and early morning. If possible, outside activities should be limited during these times.”

On September 8th, officials from the Massachusetts Department of Health and Human Services announced the state’s first human case of West Nile virus of the season. A press release from the department noted that the case, confirmed by the Massachusetts State Public Health Laboratory, involved a resident of Bristol County, a male in his fifties, who remained hospitalized at the time of the news. “This patient would have been bitten by an infected mosquito in early to mid-August which is the beginning of the peak season for possible West Nile virus human infections,” said state public health veterinarian Catherine Brown, DVM, MSc, MPH. “There have been so many WNV infected mosquitoes identified this year throughout the Commonwealth that the risk is widespread and ongoing. That means that this year, it is extremely important to take steps to avoid mosquito bites including using repellents, using clothing to reduce exposed skin, dumping standing water, and moving indoors when you notice mosquitoes biting you.”

In additional news, on September 6th, Colorado’s Larimer County Department of Health and Environment reported the state’s first West Nile virus death of the year. The case involved a resident of Fort Collins who died after developing a neuroinvasive form of the virus. Larimer county has reported 4 cases of West Nile so far this season, 2 of which have been neuroinvasive.

Despite the fact that mosquito numbers tend to drop in September, health officials say the risk of West Nile will continue in the area until it sees its first frost of the season. “The biggest months for human West Nile virus cases in Colorado are August and September,” said state public health veterinarian Jennifer House, DVM, MPH, in a recent statement. “When vacations are over, and the kids go back to school, it’s easy to forget mosquitoes are still out in force. We want to remind people to keep using insect repellent and other methods to avoid mosquito bites.”