Hanging from walls and tucked into garden nooks, the simple but effective 'ovillantas' made from recycled tyres look something like man-made mosquito hatcheries
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Ovillantas - used tyres make a new and affordable mosquito trap in rural Mexico
2nd November, 2016
The Mexican Government spends millions trying to stop the spread of mosquito-borne viruses like dengue, chikungunya and - more recently - zika. Could the solution be as simple as a kind of mosquito ‘hatchery' made of old tyres to create an inviting breeding ground from which eggs and larvae can be destroyed? FOREST RAY reports.
The only really definitive way to measure the effect that ovillantas have on disease transmission is to measure the rates of infection in areas with and without ovillantas
Strange objects adorn the walls of people's houses in Troncones - a small town in Mexico's Guerrero state that lies half hidden to the north of its better-known neighbours, Ixtapa and Zihuatanejo.
These objects are in fact used car tyres, cut into two sections and resting on each other to form an oval with a small opening into a dark interior.
A plastic tube with a tap protrudes from the bottom section. The interior of each of these objects consists of roughly half a litre of water with a strip of paper floating on top of the surface.
Mosquito eggs float on this same water and stick to that paper and if you look closely, you will see mosquito larvae also wriggling through the water, agitating its surface.
Hanging from walls and tucked into garden nooks surrounding the homes in this Mexican village, the tyre contraptions are called ovillantas (from the Latin ovi for egg and the Spanish llanta, for tyre) and are the latest tool in the fight against mosquito-borne viruses here in Mexico.
Dengue, chikungunya and more recently zika together inflict considerable damage on both Mexico's economy and the health of its people. As of 2011, Mexico was estimated to have spent roughly $170 million on efforts to control the mosquito that carries dengue.
The three viruses are transmitted by two closely related mosquito species: Aedes aegypti and Aedes albopictus. Zika is still too new to the scene to accurately estimate its full impact, but it carries with it, of course, an outsized emotional burden, thanks in great part to the increased risk of microcephaly in newborns.
A low tech solution for the age of austerity
The cost of mosquito control presents a significant challenge in the fight against these diseases. Nearly all public health efforts in Mexico are government-sponsored, but as is heard all too often here, "no hay dinero" (there is no money). There is also very little money in the pockets of the average Mexican citizen further complicating any individual effort to combat mosquitos and the diseases they carry.
As global warming and an increasingly interconnected world stoke growing fears of rapidly spreading diseases, what is very clear is that Mexico struggles to find cost-effective ways to fight the ones that have already taken root in its territory.
Enter Dr Gerardo Ulibarri. A native of Michoacán State in Mexico and a researcher at the Laurentian University in Ontario, Canada, he specializes in fighting mosquito-borne diseases through low-cost (and therefor affordable) methods. And with his ovillantas, he is hoping to have picked a winner.
By providing aedes mosquitoes with ideal egg-laying grounds in known locations, the ovillantas serve as traps that allow people to destroy any eggs and larvae found within them, thereby limiting their population growth. It is a simple system, consisting of nothing more than the aforementioned tyre sections, paper, a spigot, some water and crucially, regular attention by way of maintenance and checking for eggs and larvae.
The ovillantas were born of necessity. Dr. Ulibarri had been working on low-cost solutions to mosquito control efforts in his native Mexico for some time. He had already seen some success in an earlier mosquito trap design, called an ovitrampa, which he had field-tested in the town of Petatlán, in Mexico's southwestern Guerrero state.
Unfortunately, the company that made the ovitrampas failed to deliver during a field test in Guatemala, forcing Dr Ulibarri to improvise with materials he could find close at hand.
Cheaper, better, more secure
As it happened, this proved fortuitous because it led to the creation of the ovillantas, which have some advantages over the ovitrampas. Firstly, the materials used and simple construction of these traps is much cheaper. Secondly, the ovitrampas had consisted of large plastic buckets, which would often be stolen. (The average person, it seems, finds plastic buckets much more useful than chopped up car tyres!)
Meanwhile in Troncones, chikungunya, dengue and zika had struck with force. Whole families fell ill, losing weeks of wages. Several people died. Property owners, who tend to be the main employers in Troncones came together to investigate ways to prevent this from occurring again and soon came across Dr Ulibarri's ovillanta trials.
The project in Guatemala had demonstrated the ovillantas' efficacy in reducing aedes mosquito populations and so Dewey Mcmillan and Jill Edwards, two of the property owners in Troncones, contacted Dr Ulibarri about establishing ovillantas in their community.
This led to a mutually beneficial arrangement for all parties involved. Dewey and Jill set up a GoFundMe campaign and raised enough money to place roughly 200 ovillantas in and around Troncones (there are more on the way) and to fund their maintenance for approximately two years. This enables Dr Ulibarri to run a bigger and longer field trial than previous trials.
With this development, he hopes to acquire data that will be critical to the future of ovillantas both in Mexico and beyond.
Community participation essential!
Despite the funds raised so far, the group of landlords and researchers still face a number of obstacles. Given that without constant vigilance, ovillantas really are just mosquito breeding grounds, not everyone in the town has embraced the idea of putting them in and around their property.
Because successful implementation of the ovillanta system relies so heavily on community participation, public training and communication forms a considerable part of the research effort. As Dr Ulibarri explains, the social obstacles to implementing the ovillantas are twofold:
- they first had to convince people to actively participate in the maintenance of the ovillantas themselves
- and then they needed to encourage even more people to adopt the good anti-mosquito hygiene practices that support the success of the ovillantas.
Maximizing the potential benefit of the ovillantas requires effort even on the part of neighbours who haven't placed an ovillanta in their garden.
Mosquitos are opportunistic and will lay their eggs in any safe place that they can find. Limiting access to other dark, protected sources of standing water around Troncones makes the ovillantas all the more appealing to the mosquitos and the more mosquitos that lay eggs in the ovillantas, the more the eggs can be destroyed.
The aedes mosquitos also have an extremely limited flight range. An individual aedes born in someone's yard might never even cross the street. In this way, keeping one's house and yard free of standing water offers protection to nearby neighbours.
Although it is unrealistic to expect that all aedes mosquitos in a given area can be destroyed in this way, restricting their population size is expected to have a profound effect on their ability to transmit disease.
The fewer mosquitos there are to transmit the disease, the fewer people will get infected. The fewer infected people there are, the less likely a mosquito will be able to transmit a disease from an infected person to a healthy one. The two effects complement each other.
The good news: it seems to be working ...
The people working on the ovillanta project express optimism at the level of participation, enthusiasm and acceptance the project has generated so far. Preliminary results from the ovillantas in Troncones look promising.
Over the four months that the project has been running, egg counts in the ovillantas have already diminished significantly. At the latest count, an estimated 128,200 eggs had been destroyed. From hundreds of eggs per trap initially, the group now counts eggs in the dozens.
Assuming no significant increase in other options for mosquito breeding grounds, this indicates that fewer aedes mosquitos are laying eggs and therefore suggests that the ovillantas are having an effect.
As long as aedes mosquitos are around, of course, the possibility of virus transmission exists. The only really definitive way to measure the effect that ovillantas have on disease transmission is to measure the rates of infection in areas with and without ovillantas.
Although the disease rates in the Troncones area seems to have lessened significantly compared to last year, as measured by job attendance among hotel staff, accurately measuring the rate of mosquito-borne illness is not a trivial task. While there is no technological barrier to accurately diagnosing mosquito-borne viruses exists, there is an economic barrier - at least here in Mexico.
The cost hurdle that excludes the poorest patients
Blood tests exist to identify each virus that the aedes mosquitos transmit. But as Dr Gustavo Velazquez, a physician at the local clinic in Troncones explains, the cost of these tests and the logistical challenges of transporting them to village clinics and sending them to labs makes their use very impractical in many Mexican settings. Furthermore, some tests, such as for zika, can be inconclusive, requiring even further testing.
In Troncones, the average daily wage is only MX$150, or roughly US$7.95 (as of 9 September 2016. Note: that this wage value is anecdotal, due to a combination of irregular jobs and the lack of official wage records.). After paying for food, transport to and from work and school and utility bills, blood tests appear unrealistically expensive for many people.
Generally, clinics will only offer the tests to high-risk cases, such as when zika is suspected in a pregnant patient. Besides the cost, the other big reason for not performing blood tests to accurately diagnose each virus is that there are no cures on hand for any of them.
This means that in all cases, treatment is designed to manage the symptoms and there is considerable overlap between the symptoms of each virus. The symptomatic management of the diseases also means that many people, knowing this, simply buy aspirin and self-treat, rather than visiting the doctor, which further obscures accurate case counts.
Largely because of this, Dr Velazquez says that he cannot accurately say how the number of cases of mosquito-borne viruses has changed lately. The one disease that he can confidently say has diminished is dengue, but this could be due in part to increases in zika and chikungunya over the past two years.
As far as we know, the mosquitos can only carry one virus at a time, so as more of them pick up the newer viruses, fewer will carry the older ones like dengue. Dr Velazquez sends his epidemiological data to the Department of Health, which is tasked with compiling all such data and making it public. This is not a fast process, however and it will likely be several years before this year's data is published.
The technology is spreading around the world
Since the publication of Dr Ulibarri's paper describing the ovillantas, other research groups in New Zealand, Brazil, Colombia, Argentina and Florida have now set up similar field tests and trials. And despite the hurdles still facing the commercial development of the ovillantas, Dr Ulibarri is optimistic about the project's future.
In the short term, he hopes to encourage greater community enthusiasm for and understanding of the project and to acquire more data concerning disease rates and mosquito population counts. This will make his longer-term goal of getting government help easier in the future.
Ultimately though, he says, only governments and NGOs have the financial and political resources to make the ovillantas solution a long-term reality and successful solution in tackling mankind's greatest pest - the mosquito.
Dr Forest Ray holds a PhD in biochemistry from Columbia University. He has published a dissertation on genomic sequencing technologies and has a paper on low-cost sequencing methods under review. He currently lives in Mexico, where he has gained an interest in how scientific research is used to improve public health when research budgets are constrained.
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