Pinellas County a Model for Mosquito-Borne Disease Surveillance

Florida mosquito control officials may learn to emulate Pinellas County’s mosquito-borne disease surveillance program and its response to a West Nile virus outbreak in 2005, a University of Florida entomologist says.

“They have a top-notch mosquito surveillance program in Pinellas County,” said professor Jonathan Day, a faculty member at the Florida Medical Entomology Laboratory, part of the UF Institute of Food and Agricultural Sciences. “That’s the model that we always go back to. They averted a much larger West Nile epidemic in 2005.”

Day will speak April 26 at the Southwest Regional Workshop on Arboviral Surveillance in Lehigh Acres, Fla. The workshop is organized by the Florida Mosquito Control Association and FMEL, and participants will analyze the 2011 and 2015 South Florida surveillance data regarding mosquito-borne viruses.

In this case, “South Florida” is comprised of roughly an area from Hillsborough east to Indian River and south to Miami-Dade County, Day said.

One key method of determining whether a region has a mosquito-borne virus is to test blood from sentinel chickens to see whether they’ve been bitten by an infected mosquito. Sentinel chickens will show mosquito control officials whether West Nile, Eastern equine encephalitis or St. Louis encephalitis virus is in mosquitoes attracted to the sentinel chickens.

Those same mosquitoes may bite and infect humans. In 2005 in Pinellas County, 18 people contracted West Nile virus, Day said. This came after 27 sentinel chickens tested positive for the virus. County officials then worked with state officials to issue a medical advisory for the county and launched mosquito control in the areas around the chickens that tested positive. With those actions, Pinellas County reduced the potential severity of the West Nile outbreak, Day said.

About 1 in 5 people who are infected with West Nile virus will develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea or rash, according to the Centers for Disease Control and Prevention (CDC). Most people with this type of West Nile infection recover completely, but fatigue and weakness can last for weeks or months. Less than 1 percent of those who are infected will develop a serious neurologic illness such as encephalitis or meningitis.

In a paper published last year in the Journal of Medical Entomology, Day helped document Florida’s likelihood of experiencing another West Nile virus outbreak, despite lower prevalence of the virus in recent years. In fact, last year, Florida reported 372 West Nile-positive sentinel chickens, according to figures supplied by Day. That’s down from a high of 1,346 West Nile-positive sentinels reported in 2003.

Other numbers for the viruses in Florida:

• 12 St. Louis encephalitis-positive sentinel chickens in 2015; compared to a high of 1,037 positive sentinels in 1990.
• 79 eastern equine encephalitis-positive sentinel chickens in 2015; compared to a high of 342 positive sentinels in 2005.

Source: University of Florida Institute of Food and Agricultural Sciences