Wisconsin has experienced a record high number of cases of West Nile Virus this year, and until the first frost, residents could still be at risk.
Paul Biedrzycki, the City of Milwaukee Health Department’s director of disease control and environmental health, said that state-wide, there have been about 40 cases with 3 deaths.
Biedrzycki said more than half of the cases have been in Milwaukee County, with a quarter of all cases occurring in the city.
“For the U.S. overall, we are seeing the highest number of reported cases through the first week of October since 2003, the year with the previous highest number of cases,” said Candice Burns Hoffman, a health communication specialist for the Centers for Disease Control and Prevention.
Biedrzycki said it will most likely be a record year for the virus.
Wisconsin saw the most cases of the disease in 2002, with 48 cases, and 2006, with 21 cases.
According to Hoffman, the CDC received a total number of 3,969 human cases of West Nile Virus, including 163 deaths this year.
“Most of these individuals are over 50 years of age, and we’ve received most of our reports in the last month,” Biedyzycki said. “We typically see the peak of West Nile Virus infections in August.”
Biedrzycki said the reason we see the emergence of the West Nile virus in August and September is because the disease has a two- to three-week incubation period.
“Thankfully, the worst of the year may be over,” Hoffman said. “Based on West Nile virus seasonal outbreaks in previous years, we expect that the peak of transmission occured in mid- to late-August and the number of infections will decrease over the next several weeks.”
Hoffman said it will be difficult to predict how many cases will arise over the next few weeks because of the various factors that affect West Nile transmission.
“The warm weather has also made mosquito populations lingering,” Biedrzycki said.
The culex pipiens mosquito is the predominant transmitter of the disease. Although it doesn’t prefer to bite humans, it is known to bite birds, which is how the disease is transmitted.
“You need the mosquito to bite birds to transmit the disease,” Biedyzycki said “The culex pipiens likes hot dry weather, yet we don’t know the exact cause why the disease is blooming and causing deaths. This is really an unusual year.”
This unusual year has consisted of long drought-like conditions with unusually high temperatures, which is the environment the culex pipiens thrives in.
“I don’t think it’s cause for alarm, but I do think it’s a real public health issue which we are following very closely,” Biedrzycki said. “We are trying to get the message out to the public, which is a little complacent because mosquitos haven’t been bad this year. Mosquito biting hasn’t been bad, but the West Nile virus is bad.”
Biedrzycki said that the threat of West Nile ends after the first frost of the season, but the Milwaukee Health Department won’t know the total number of cases until a few weeks pass after the frost.
Until then Biedrzycki is urging that to prevent further breeding of the culex pipiens, residents should empty all stagnant water and wear long sleeves and pants while applying mosquito repellent.
“My suspicion is that it is climate related: The weather favored this particular mosquito, and people let their guard down around this mosquito,” Biedrzycki said. “I can assure you that before next year we will better understand what is happening.”
The CDC said the best way to prevent West Nile Virus is to use insect repellents when going outdoors, wear long sleeves and pants during dawn and dusk and install or repair screens on windows or doors and to use air conditioning.