Beginning in 2016, Dr. Gerardo Ulibarri, a researcher with the Laurentian University in Canada, began placing a special kind of mosquito trap around the town of Troncones, on the Pacific coast of Mexico’s Guerrero state.
These traps, called ovillantas, have proven successful in dramatically reducing the population of the Aedes aegypti mosquito and of the zika and chikungunya viruses that they can carry.
The ovillanta trap consists of a used car or truck tire, cut into two sections to form an oval with a small opening into a dark interior. A plastic tap protrudes from the bottom section. Roughly half a litre of water with a strip of paper floating in it occupies the lower section. Mosquitos lay their eggs upon the water, which then stick to the paper. Every 2-3 days, the water is drained and the egg-laden paper destroyed and replaced.
The water is also replaced into the ovillanta. When mosquitos lay eggs, they emit pheromones that signal to other mosquitos that a given place is safe. The pheromone-rich water in the ovillanta, therefore, serves as an attractant to other mosquitos, drawing them into the trap. Although the pheromones work as a natural attractant, Dr. Ulibari continues to experiment with other, potentially more effective attractants.
Dr. Gustavo Velázquez Vélez, of the Troncones public health clinic, asserts that of the three main mosquito-borne illnesses found in Troncones – dengue, zika and chikungunya – the latter two have effectively vanished since the introduction of the ovillantas.
In 2015, Dr. Velázquez recorded 32 cases of chikungunya. In 2016, he recorded 37 cases of zika, with 3 cases affecting pregnant women. He recorded no cases of either disease from 2018 through May of 2019, the time of writing this article.
Dengue cases have dropped as well, although not in a statistically significant manner. Whereas zika and chikungunya are relative newcomers to the area, dengue has long been endemic. As such, it is present at lower rates, owing to more natural resistance within the local population and is harder to eradicate, due to occupying a wider geographical area.
Between 2015 and 2017, Velázquez recorded 5-9 cases of dengue per year. 2018 saw a notable drop, to zero recorded cases and in 2019, Velázquez saw only three cases of “probable dengue”, none of which was considered “serious”. Although tempting to draw the conclusion that dengue is on the retreat, the low number of overall cases make this a shaky proposition.
That said, the apparent local eradication of zika and chikungunya, along with the very low rate of dengue, is good news for Troncones, which is located between the popular tourist destination of Zihuatanejo and the quickly-growing surf destination of Saladita.
Dr. Ulibarri wishes to expand his ovillanta project throughout Mexico and beyond. This desire, unfortunately, faces some challenging obstacles. First, zika cases are down across Mexico as a whole (pdf, in Spanish, from Mexican government), which has led to a drop in public interest regarding sustained measures to control not only zika, but mosquito populations in general. While this is good news, a failure to sustain control measures raises the risk of relapse.
Second, the government has not provided Dr. Ulibari with the funding that he has sought, to expand the ovillanta project. As it stands now, small local projects like that in Troncones are funded by donations and kept alive through a very small number of dedicated volunteers. This works in a tight-knit and well-functioning community such as Troncones, but will need greater assistance to implement at scale.
Note: Post edited to clarify Dr. Gustavo Velázquez Vélez’s professional name as Dr. Velázquez, whereas he was previously referred to as Dr. Vélez.