Mosquito Control Efforts Reducing Chikungunya Rates in Puerto Rico?

The use of autocidal gravid ovitraps developed by the US Centers for Disease Control and Prevention (CDC) that target chikungunya and dengue-carrying Aedes aegypti mosquitoes has reduced mosquito density tenfold in 2 Puerto Rican municipalities, according to a report published in the Morbidity and Mortality Weekly Report.

Tyler M Sharp, PhD, of the Division of Vector-Borne Diseases at the National Center for Emerging and Zoonotic Infectious Diseases at the CDC and colleagues said that in turn, disease transmission may be reduced as well.

In addition to carrying chikungunya and dengue, female Aedes aegypti mosquitos also carry the Zika virus. They are active during the day, and are most often are found in and around home environments. “Conventional vector control approaches often fail to result in effective and sustainable prevention of infection with viruses transmitted by Aedes mosquitoes,” Dr Sharp and colleagues wrote in the report.

The traps attract and catch female Aedes aegypti that transmit disease without the use of pesticides. The traps are simple, low-cost and do not need servicing for long time periods. The report noted that 4 communities in the municipalities of Salinas and Guayama in Puerto Rico have field tested these traps since 2012. Two communities used 3 traps per house, and also used randomly distributed surveillance traps. The other 2 nonintervention communities only used surveillance traps.

The researchers reported that, “from June 2014 to December 2014, after the identification of the first laboratory-positive chikungunya case, the average densities of Ae. aegypti female mosquitoes were 1.1 and 11.6 per surveillance trap per week in communities with and without control traps, respectively” and this tenfold difference between intervention and non-intervention areas continued through 2015.

Dr Sharp and colleagues explained that, overseen by a CDC Institutional review board, a study was conducted on 620 households on residents older than age 5 from both intervention and nonintervention communities and serosurveyed them for illness, along with giving participants a questionnaire on household demographics, recent illness and personal mosquito control methods. Data were collected between November 2015-February 2016. After data were processed and adjusted for sample design, the study researchers concluded that chikungunya virus IgG antibody from the intervention areas was half that of nonintervention areas.

The report noted that the CDC only produces traps in limited numbers, and that private sector companies are being located and encouraged to mass produce the traps for surveillance and control of female Aedes aegypti mosquitoes.

In an interview with Infectious Disease Advisor, Dr Sharp explained, “We are continuing to analyze the data collected from the serosurvey in Salinas to perform a more complete geospatial analysis and identify additional factors, behavioral or otherwise, associated protection from infection with chikungunya virus.”

Dr Sharp also said that the study was important to physicians because it helps provide prevention advice. ”In addition to recommending that patient avoid mosquito bites by using mosquito repellent, staying in residences with air conditioning and/or intact screens on windows and doors and wearing pants and long sleeve shirts,” he said during the interview, “appropriate use of the AGO traps in communities may be an additional approach to avoid infection with pathogens transmitted by Aedes aegypti mosquitoes.”

Dr Sharp concluded the interview by adding that, “although the AGO traps were associated with protection from infection with chikungunya virus, there was still a >20% rate of infection in communities where the traps were present.” He advised that the use of multiple strategies to avoid Aedes aegypti mosquito bites will “be necessary to avoid infection with chikungunya, dengue or Zika viruses.”

Reference

Lorenzi OD, Major C, Acevedo V et al. Reduced incidence of chikungunya virus infection in communities with ongoing Aedes aegypti mosquito trap intervention studies — Salinas and Guayama, Puerto Rico, November 2015–February 2016. MMWR. 2016;65:18. DOI: http://dx.doi.org/10.15585/mmwr.mm6518e3.