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Insecticide resistance, herd immunity raise concerns for future dengue epidemics
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New data from a dynamic model of dengue transmission highlight the importance of reassessing vector control policies — based upon larva control alone — for the control of future dengue epidemics.
“While the study shows that larval and adult control, when applied with specific efficacies and application frequencies can reduce the health burden imposed by dengue, there is a need to keep a vigilant eye on the resistance profile of the mosquito population and on future dengue transmission dynamics,” Paula Mendes Luz, PhD, of Yale University School of Medicine, told Infectious Disease News.
Although the control of dengue relies heavily upon insecticide, resistance to insecticide may lead to the failure of current dengue control programs, according to background information in the study. For this reason, Luz and colleagues developed a dynamic model of dengue transmission to evaluate the evolution of insecticide resistance and herd immunity in a cohort residing in Rio de Janeiro, Brazil. Follow-up was 5 years.
Researchers conducted a cost-effectiveness analysis of 43 insecticide-based vector control strategies targeted at larval and adult mosquitoes at high, medium and low efficacy (mortality, 90%, 60%, 30%); one to six yearly application frequencies were conducted to estimate the effect of health and health economic outcomes.
Compared with three or more applications of adult mosquito vector control that reduced dengue burden by 4 years, high-efficacy larval control applied at least once reduced the burden for 2 years. However, all control strategies were associated with insecticide resistance.
The model projected that if the cost of adult mosquito control was more than 8.2 times the cost of larval control, then all strategies based upon adult control became dominated, according to the study. The researchers suggested that six high-efficacy adult vector control applications per year would likely meet WHO standards for a cost-effective intervention.
“To better inform future cost-effectiveness analyses, vector control resource use and field-based evaluations of insecticide-based vector control efficacy are important areas for further investigation,” Luz said.
In an accompanying editorial, Eduardo Massad, PhD, and Francisco Antonio Bezerra Coutinho, PhD, both of the University of São Paulo in Brazil,wrote: “[These] results refer to use of high-efficacy adulticides, not the low-efficacy adulticides used in most dengue-control programs. Practical hurdles with the use of adulticides have so far rendered this method to be a control strategy with limited effectiveness. To achieve the results obtained with the high-efficacy adult-control strategies proposed by Luz and colleagues, new insecticides and better methods of application are urgently needed.”
Disclosure: The researchers report no relevant financial disclosures.
The Aedes aegypti mosquito responsible for most dengue transmission globally is a formidable foe from a vector control perspective: Adults are often found indoors, making them inaccessible to widespread outdoor adulticide applications, and the multitude of cryptic breeding sites in modern urban settings severely limits larviciding effectiveness. Unfortunately, given the low efficacy pesticides currently available, the potential benefit of high efficacy adulticides predicted by the elegant mathematical model created by Luz and colleagues is not likely to be realized anytime soon. Sadly, even the model's limited predicted impact of low efficacy pesticides seems optimistic given the near universal failure of contemporary dengue control efforts.
– Lyle R. Petersen, MD, MPH
Infectious Disease News Editorial Board member
For more information:
- Luz PM. Lancet. 2011;doi:10.1016/S0140-6736(11)60246-8.
- Massad E. Lancet. 2011;doi:10.1016/S0140-6736(11)60470-4.
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