Researchers at LSTM have called for higher quality standardised research in order to assess the impact of vector control to prevent virus infections transmitted by Aedes aegypti mosquitoes, such as dengue fever, chikungunya and Zika.
Dengue fever is a mosquito-borne tropical infection that mostly causes flu-like symptoms but can occasionally develop into a potentially life threatening condition called severe dengue. The global incidence of dengue has increased dramatically over the past 50 years and today it is the most widespread mosquito-borne arboviral disease, affecting nearly half the world’s population in 128 countries. Although a vaccine could be available soon, control of Aedes mosquitoes remains the primary approach used to prevent dengue.
The study, carried out by LSTM’s Leigh Bowman and Philip McCall with Sarah Donegan of the University of Liverpool, reviewed the literature from the past 35 years for evidence of the effectiveness of all vector control methods in reducing dengue transmission. The findings are published this week(link is external) in the journal PLOS Neglected Tropical Diseases.
From 960 studies, 41 were eligible for inclusion with 19 suitable for meta-analysis. Methods investigated ranged from community-based clean-up projects to release of genetically-modified mosquitoes, but fewer than a quarter of studies were randomized controlled trials (RCTs), none of which recorded any impact on dengue transmission. Dr McCall added: “Remarkably, no RCTs evaluated effectiveness of insecticide space-spraying (also called outdoor fogging) which is the number one method used in response to dengue outbreaks virtually everywhere today”.
On a positive note, limited evidence indicated that screening the doors and windows of houses and to a lesser extent, community-based environmental management with water container covers, could reduce risk of dengue infection. Skin repellents, bed nets and mosquito traps had no effect on risk of infection while insecticide aerosols and mosquito coils were associated with slightly higher risk. However, as the quality of studies was poor overall, the evidence remains very weak, compromising the knowledge base for making recommendations on delivery of appropriate and effective control. In simple terms, this means that we do not have a clear understanding of which of the currently available interventions actually work, where or when they succeed or might work best, and the reasons why they succeed or fail.
Dr McCall continued: “The dramatic growth in dengue over the past 35 years has been a remarkable epidemiological event and, as evidenced by its continued global spread, a challenge for which the public health community was not prepared. The paucity of reliable evidence demonstrated by this review is of major concern. With dengue outbreaks occurring at increasing frequency and intensity, and the emergence of chikungunya and Zika viruses, it is vital that we understand which of the control tools at our disposal are effective.” The authors call for a global independent advisory body to guide decisions regarding the selection of approaches and tools for control or prevention of infections transmitted by urban Aedes sp. vector populations, and the design of appropriate multi-centre trials to evaluate their effectiveness.