Electronic mosquito repellents don't prevent bites and therefore don't prevent disease transmission, according to a new study.
"EMRs should not be manufactured, advertised or used for mosquito bite and malaria prevention, as they do not do so," said lead author A. Ali Enayati, Ph.D., lecturer in medical entomology at the Mazandaran University of Medical Sciences in Sari, Iran.
The review appears in the latest issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
The researcher analyzed 10 studies conducted in North America, Russia and Africa. All were field-based studies ó occurring in a natural setting rather than a laboratory.
All studies "found that there was no difference in the number of mosquitoes that landed on the bare body parts of the human subjects with or without an EMR," Enayati said. "Hence, these devices do not work in repelling mosquitoes. As EMRs do not repel mosquitoes, they would not prevent malaria."
Malaria, which kills more than a million persons every year, is most deadly among children and is particularly prevalent in sub-Saharan Africa. It is transmitted by female Anopheles mosquitoes infected with the malaria parasite. No vaccine against malaria is available.
EMRs are small, handheld devices that emit a high-frequency buzz almost inaudible to the human ear. Manufacturers claim that the buzz mimics the beating of male mosquito wings. EMRs are used indoors and outdoors and are purported to repel mosquitoes within a range of 2.5 meters ó about 8 feet.
Females are supposedly repelled by the sound, since they mate only once in their lives. However, some researchers have reported that female mosquitoes have a very weak sensitivity for any sound.
The authors say that 30 years of scientific skepticism and a successful prosecution in the 1980s of EMR marketers under the UK Trade Description Act has not affected worldwide marketing of the devices. "This is a concern," they write, "because it is likely to lead to consumers not using other protective methods that are proven to work." Such personal protection includes mosquito repellents formulated as pills, ointments, lotions and sprays, as well as insecticide-treated or untreated bed nets.
Study investigators had counted mosquitoes landing on bare body parts ó mostly arms, legs and feet ó during specified time periods in which an EMR was switched on or off.
There were no significant differences in the landing rates with and without EMR, making the devices ineffective for preventing malaria transmission.
"I agree with the Cochrane report," said Joel Breman, M.D., a senior scientific advisor at the Fogarty International Center of the National Institutes of Health. "There is no evidence that electronic devices prevent malaria and many other available options should be used. For example, insecticide-soaked bed nets kill female mosquitoes on contact or repel them from the house during the biting hours, from dusk to dawn."
While also in agreement with the review's conclusion, Nirbhay Kumar, Ph.D., professor of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health, added one qualification.
"Seven of 10 studies analyzed focused on non-anopheline mosquitoes and only three included [the type of mosquito that transmits malaria]," Kumar said. "Perhaps a few confirmatory studies focusing in only malaria-endemic areas may either completely support their analysis or provide some hope for malaria control by this method, if at all applicable."