Researchers at the Icahn School of Medicine at Mount Sinai are working on computer models that can predict outbreaks of West Nile virus and improve the public health response.
In their latest work, a new study examined the time lag between the first reports of the virus to public health officials and the final confirmation and release of that information to the public. They found that the shorter the time lag, the more accurate their models became.
“The goal in all this work is thinking about the process,” said research principal Nicholas DeFelice. “We’re trying to do real-time predictions.”
If the model can make reasonably accurate predictions for West Nile outbreaks, public health officials can better manage the limited resources they have and “hopefully have better health outcomes,” he added.
Most people who get sick with West Nile have flu-like symptoms and recover. But some suffer neurological damage that takes months to recover from, if ever. The disease can also be fatal.
The study, “Modeling and surveillance of reporting delays of mosquitoes and humans infected with West Nile virus and associations with accuracy of West Nile virus forecasts,” was published Friday morning in JAMA Network Open, a monthly online publication of the American Medical Association. The study examined reporting lag times in four mosquito control districts around the country, including Chicago; Coachella Valley, California; Suffolk County, Virginia; and St. Tammany Parish, Louisiana.
The average reporting lag time for a positive mosquito sample was 6.6 days and affected the model’s accuracy by about 5 percent. However, the reporting lag time for human cases was much longer, an average of 5.5 weeks. That long lag rendered real-time forecasting of the virus outbreaks useless, the study found.
Among the regions studied, the lag in reporting human cases varied widely, from two to 14 weeks. Doctors in most of the study areas were required to report a positive diagnosis within one week, but the California doctors were required to report within a day.
West Nile virus emerged in the late 1990s. It was one of several arthropod-borne (mosquito and tick) viruses to make an unexpected leap from the Eastern Hemisphere to the Western Hemisphere, along with chikungunya, dengue and Zika. West Nile, however, is the leading cause of arboviral disease domestically and produced three of the largest outbreaks of this disease type, DeFelice wrote in his study’s findings.
Texas saw perhaps its worst outbreak in 2012, and the incidence rate in Denton County was among the highest statewide that year. Texas public health officials adjusted some of their practices after that outbreak. For example, Denton County and nearby cities joined in regular sampling during mosquito season, something Denton has been doing for 15 years.
University of North Texas biology professor James Kennedy has overseen the program between the city and the university since its inception. He says the gap between shipping a sample to the state lab and the report of a West Nile-positive sample has shortened considerably, from a week or longer to just a few days. Usually, UNT biology students prepare the samples for overnight shipments on Monday or Tuesday, and UNT and city officials know the results by late Thursday or early Friday.
After the 2012 outbreak, Denton also agreed to fund new equipment that can analyze samples within a few hours at UNT’s lab, although the results are less definitive. Kennedy said the equipment sometimes delivers false positives, but it does well as a first alert.
The UNT teams will begin collecting weekly mosquito samples starting May 6, Kennedy said. Biology student Gillian Graham said the team tried out a new kind of trap last year that attracts all types of mosquito species, including the species known to carry West Nile virus in North Texas.
The traps worked well enough that they will put out more this year.
“The attractant smells like human skin and the CO2 we give off,” Graham said. “It smells pretty bad.”
In addition, the team will be collecting other mosquito samples for a new study being funded by the Centers for Disease Control and Prevention and led by researchers at University of Texas Rio Grande Valley.
Researchers there are looking for patterns of insecticide resistance in mosquitoes that carry West Nile and other viruses.