A month after two Sterling teenagers were diagnosed with malaria, the Loudoun County Health Department trapped mosquitoes in the area that tested positive for the disease.
"This is the first time in over 20 years that positive mosquitoes have been found in conjunction with a human case in the United States," said David Goodfriend, Health Department director.
In August, a 14-year-old boy and a 19-year-old girl were treated for malaria, an infectious disease transmitted to humans through mosquito bites.
The Health Department responded by contracting Clarke Environmental Mosquito Control to spray for adult mosquitoes in the area where the infections most likely occurred. On Sept. 9, the company sprayed Anvil in a one-mile radius of the Sugarland Run Community Center. Mosquito surveillance the night after spraying showed fewer numbers of the Anopheles quadrimaculatus mosquito that can carry malaria.
"It's not as nearly as serious as West Nile virus. It's a treatable disease," Goodfriend said. "We know that West Nile virus is in our county. West Nile virus is not treatable and can kill."
The Health Department conducted human surveillance for two weeks in September by reviewing hospital records from the Loudoun Hospital and urgent care centers. The department followed up with patients diagnosed with unidentified fever and tested them if they were still sick, not finding any additional cases of malaria. Malaria symptoms can include fever, shaking chills, headache, muscle aches and tiredness, along with nausea, vomiting and diarrhea.
THE DEPARTMENT hired Clarke again to set out traps for mosquito surveillance. On Sept. 25, a mosquito trap in the Lansdowne area captured Anopheles mosquitoes positive for malaria. Two days later, a mosquito trap in the Broad Run area captured additional infected mosquitoes. One or more of the mosquitoes in the traps could have been infected since the same mosquito type was ground up and tested as one substance.
Clarke set out 10 additional traps Monday night from Lansdowne to Sugarland Run to identify if additional mosquito pools test positive for the disease. The number of Anopheles mosquitoes and the number infected will help the Health Department determine if additional adult spraying and larviciding is needed, or if additional traps should be set out.
"Our main effort now is to identify where mosquitoes infected with malaria are in Loudoun County, ... so we can take the necessary steps to keep residents safe," Goodfriend said. "Based on what we find, we may put those traps somewhere else or bring in additional traps."
The department is testing for West Nile virus throughout the county and has not identified the Anopheles mosquito in any other areas.
"We know where in the county these type of mosquitoes tend to breed. It's important for us to look in that area to see what other places within that area may have infected mosquitoes," Goodfriend said.