Spraying May Not Stop Zika-Carrying Mosquitoes

mosquito(CN) – Common mosquito control strategies like spraying insecticides to control the spread of the Zika virus can be counterproductive and are often based on unreliable scientific studies and evidence.

Reviewing previous studies on mosquito control interventions, a team of researchers found a lack of evidence demonstrating the effectiveness of standard approaches to reducing mosquito populations and the spread of the diseases they can transmit. Their findings were published Wednesday in the journal PLOS Neglected Tropical Diseases.

Several studies failed to measure how the control strategies affected the spread of certain diseases, focusing instead on reductions of mosquito populations. Other studies present varying results that didn’t reliably determine the effectiveness of some techniques.

“There is mixed evidence about whether simply reducing insect numbers actually reduces disease,” said lead author Paul Hunter. “So future research needs to cover longer durations, with better methodology, and must report on disease-related outcomes rather than just mosquito reduction.”

For chemical-control methods, the team found inconsistencies in previous studies, as some showed insecticides and larvicides reduced mosquito numbers by up to 76 percent while others showed no significant reduction.

“Although chemical measures are widely used and expected to be effective, we consider most of the evidence in favor of chemical spraying to be quite poor,” said Paul Hunter, a professor at the University of East Angola’s Norwich Medical School and leader of the study.

The World Health Organization recommends integrated approaches, which involve more than one type of control method to impact mosquitoes at all life stages, and an overall focus on communities engaging in control strategies. The WHO advises that eliminating potential mosquito breeding sites is the most effective approach.

“Although there is limited evidence relating to integrated campaigns combining multiple methods of control, the WHO is correct to reiterate that the most effective intervention is likely to be the elimination of mosquito breeding sites,” Hunter said. “This requires sustained and ongoing education campaigns.”

Health officials and vector control units have sprayed insecticides in areas where cases of Zika had been reported – a mosquito-borne virus that can be spread by Aedes aegypti mosquitoes.

After initially breaking out in Brazil in 2015, the virus has spread and been transmitted locally by mosquitoes in dozens of nations including the United States, after multiple areas in Florida were connected to domestically acquired Zika cases.

Officials in Florida sprayed insecticides from airplanes and at ground level, techniques which Hunter said could make the situation worse.

“In fact there is some evidence that spraying may be counterproductive as it generates a false sense of security such that people no longer put effort into removing mosquito breeding sites around the home,” he said.

Hunter also noted that many nations affected by mosquito-borne diseases lack the money to fully combat the local transmission of diseases, which makes it important for them to use effective techniques.

“Public health funding tends to already be quite limited in low-to-middle-income countries where mosquitoes are endemic, so more evidence on how best to spend these limited funds is essential,” he said.

“Educational campaigns and community engagement are paramount in reducing breeding habits around domestic environments and interrupting the cycle of disease transmission, but ongoing resources need to be allocated to ensure education continues and is maintained.”