The Mosquito Electrocuting Trap (MET), used to collect mosquito populations that transmit dengue virus, was recently tested for the first time. This could potentially improve the ability to determine the risk of exposure to infected bites and make disease prevention programs more effective.
Aedes aegypti mosquito during a blood meal. Photo taken by James Gathany, CDC. Public Domain: https://bit.ly/2H8Dgd0
As many of us may have experienced, mosquito bites are quite annoying and their buzzing is not pleasant either. That being said, perhaps the most important reason these tiny insects get so much attention is because women of some species of mosquitoes are able to transmit pathogens, many of which affect humans. Pathogens present in the mosquito’s salivary glands are transmitted to the human host when the female is fed a blood meal.
For example, malaria is a disease that is transmitted by Anopheles mosquitoes. Malaria is caused by Plasmodium parasites and affects hundreds of millions of people each year. Other mosquitoes, such as those of the genus Aedes, can transmit pathogenic viruses such as yellow fever, dengue fever, Zika and Chikungunya. Nowadays, dengue virus is probably the most common virus transmitted by Aedes. The incidence has increased dramatically in the past few decades, putting around half of the world’s population at risk.
To prevent the transmission of these diseases, various approaches to controlling mosquito populations have been developed. However, to make these strategies sufficiently effective, scientists need to understand where and when people are at greatest risk for mosquito bites.
The most accurate strategy is to use the HCL (Human Landing Catch) technique to catch mosquitoes at different times and locations. This consists of people exposing their own unprotected skin and trapping mosquitoes with a mouth or hand aspirator. The benefit of this strategy is that it uses natural human smells and other visual and olfactory cues that mosquitoes use to find their next blood meal.
Skin exposed to the bite of an Anopheles gambiae mosquito. Photo taken by James Gathany, CDC. Public Domain: https://bit.ly/2UDRdI3
Probably the most obvious problem with the HLC is that the participants are directly exposed to mosquito bites that may be infected. Some malaria parasites have developed drug resistance, making it risky for the HLC to test Anopheles mosquitoes. It was also more difficult to screen Aedes mosquitoes with HLC as there is no way to prevent viruses transmitted by Aedes.
In 2015, the Mosquito Electrocuting Trap (MET) was developed to trap malaria-transmitting mosquitoes as an exposure-free alternative to HLC. The MET is made up of four square, electrified, wired surfaces that are placed around the participant’s legs while sitting in a chair and the rest of the body is covered by a mosquito net. Mosquitoes can be collected and examined after receiving an electric shock when trying to get through the wired surfaces.
In a study published in January 2020, we tested the MET on Aedes mosquitoes from Ecuador for the first time. We compared its performance with the BG Sentinel Trap (BGS), which is baited with artificial smells and is the golden trapping method for Aedes surveillance.
In this 12-day study, we used two BGS traps and two METs in the outside areas of four properties in the town of Quinindé. All traps ran from 7:00 a.m. to 7:00 p.m. and were exchanged between the individual trap types every day. By the end of the study, six full days of trapping for each trap type had been completed in all homes.
Since the attractiveness of mosquitoes to people can vary from person to person, we have switched participants in the METs every hour of the collection to reduce possible bias. Finally, we measured the microclimate conditions at each catching station with data loggers.
Participant using the mosquito electric shock trap prepared to collect host-seeking mosquitos. Photo by Leonardo Ortega-López.
Impressively, we found as many Aedes mosquitoes with the METs as with the BGS traps, and we were able to record the same mosquito species with both capture methods. We found that Culex quinquefasciatus was the most common mosquito species, followed by Aedes aegypti, Aedes angustivittatus, Limatus durhami and Psorophora ferox.
With the MET, we were also able to accurately record the bite activity time of Ae. Aegypti and the other very common mosquito Cx. quinquefasciatus, which has been considered as a vector for West Nile Virus. We found that the females of both species had higher biting activity in the early morning and late afternoon. Biting activity was also negatively related to temperature.
Frequency of female Aedes aegypti per hour, a) total hourly frequency and b) comparison between the two fishing methods.
No infected mosquitoes were caught during our experiments, but we see that the infection rates of arboviruses tend to be very low in Aedes mosquitoes. Therefore, we can confirm that the main benefit of MET is the accurate estimate of mosquito bite rates and potential entomological inoculation rates (rate of infected bites) when infected mosquitoes are found.
A huge advantage of the MET is that it can be used to calibrate other trapping methods and, in combination with other traps, to monitor mosquitoes on a large scale.