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New mosquito traps offer nontoxic alternatives in Zika fight
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Canadian and Mexican researchers have developed a novel, low-cost and effective method for capturing and destroying Aedes spp. mosquito eggs by using traps made from used tires. This new solution to mosquito control, which does not use pesticides or noxious chemicals, may have implications for the prevention of vector-borne diseases like dengue and Zika, they said.
“We decided to use recycled tires — partly because tires already represent up to 29% of the breeding sites chosen by the Aedes aegypti mosquitoes, partly because tires are a universally affordable instrument in low-resource settings, and partly because giving old tires a new use creates an opportunity to clean up the local environment,” Gérardo Ulíbarri, PhD, associate professor of chemistry and biochemistry at Laurentian University, Ontario, said in a press release.
Low-cost ecological ‘ovillantas’
Over the course of 10 months in a remote community in Guatemala — where dengue, chikungunya and Zika viruses are endemic — Ulíbarri and colleagues studied the effectiveness of a mosquito egg ovitrap called an “ovillanta.” The device, which is designed to imitate a natural breeding site for mosquitoes and attract egg-laying females, is fashioned from two sections of a used car tire that overlap in the shape of a mouth. According to the researchers, a nontoxic attractant solution is poured into the bottom half of the trap, which has a fluid release valve. Female insects lay their eggs on strips of pellon paper inside the ovillanta, and the eggs are counted to monitor the density of the mosquito population and then destroyed with fire or ethanol. Once emptied, the solution is filtered and used again, building up a higher concentration of a natural pheromone left with each egg that will attract other female mosquitoes to the site.
In the study, Ulíbarri and colleagues compared the ovillanta with standard ovitraps made from buckets containing 1 L of clean water. According to the researchers, the contents of standard ovitraps are typically discarded onto the ground instead of being recycled, which can sometimes allow surviving Aedes eggs that did not adhere to the strip to hatch on dry soil up to several months later. Moreover, the need to replace clean water on a regular basis can be challenging in remote areas with limited infrastructure.
Figure 1. Ovillanta being made in Guatemala.
Figure 2. An ovillanta is created from two 50-cm sections of an old car tire, fashioned into a mouth-like shape, with a fluid release valve at the bottom.
Source: Daniel Pinelo
Eighty-four ovillantas were used in seven neighborhoods in the urban core of Sayaxché, which has a population of approximately 15,000.
Results indicated that significantly more mosquito eggs were trapped using the ovillantas — more than 181,000 eggs were destroyed during the 10-month period using the new method, almost seven times as many as control sites.
The design of the ovillanta was modeled after a prototype developed at Laurentian University in response to a West Nile virus outbreak in Ontario, and which targeted the species Culex pipiens and C. restuans. Those traps resulted in a 90% reduction of adult mosquitoes in areas where they were installed during a 3-month period, according to Ulíbarri and colleagues. The same design was used again in 2013-2014 in Mexico, effectively reducing A. albopictus and A. aegypti — both carriers of dengue virus — by 71% at the site where the modified ovitraps were used compared with a control site.
The researchers noted that, anecdotally, there were no new autochthonous cases of dengue reported in the neighborhoods of the Guatemalan community where the intervention was used. These areas are expected to have two to three dozen cases in that time frame. However, the study was not designed to monitor the intervention’s impact on viral transmission.
“We remain cautious and will continue to monitor the epidemiology closely,” Ulíbarri and colleagues wrote.
Other key components of the intervention focused on web-based training of local health care workers in vector control, as well as active participation from the community, the researchers said.
“While in its early days, this integrated innovation of a mosquito trap coupled with training local health workers and engaging communities in vector control is a promising example of how Canada’s leadership in development innovation can respond to public health emergencies such as Zika,” Peter A. Singer, OC, MD, MPH, FRSC, chief executive officer of Grand Challenges Canada, which supported the study, said in the release.
Other innovations with nontoxic ovitraps
Argentinian researchers from the Centro de Investigaciones de Plagas e Insecticidas (CIPEIN) also have designed a new ovitrap prototype — a cup made of low-density polyethylene infused with the larvicide pyriproxyfen, a WHO-recommended juvenile hormone analog that targets mosquito larvae during the pupal stage of development. Once the cup is filled with water, the larvicide is released from the plastic container, killing the eggs of A. aegypti mosquitoes.
Figure 1. These are larvae of the Aedes aegypti mosquito, the primary vector of Zika, dengue, chikungunya and yellow fever.
Source: Matt Barton
“This is a great idea,” Grayson C. Brown, PhD, an entomologist at the University of Kentucky who was not involved in the study, said in a press release. “Pyriproxyfen likes to move around in the environment. Molding it into the plastic like that keeps it where you put it.”
The CIPEIN researchers tested the plastic ovitrap on laboratory-raised A. aegypti and found that the device was 100% effective at preventing larvae from developing into adults during a 30-week period, even after the water in the container had been changed once a week. However, the researchers noted that field trials are necessary to test the prototype’s effectiveness to suppress A. aegypti populations.
“To be a practical tool for managing dengue vectors, a trap must be specific, effective, inexpensive, simple to construct and operate, and it should not require frequent maintenance,” the researchers wrote. “Traps without toxic pesticides are more likely to be accepted by homeowners concerned about potential health and environmental hazards. The prototype in our study meets all these requirements.” – by John Schoen
Disclosure: The researchers report no relevant financial disclosures.
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