On the Ground in Florida with Oxitec’s Derric Nimmo

September 15, 2016

On November 8, Florida Keys residents will get to vote on whether they want Oxitec to release its genetically engineered mosquitoes in a local scientific trial, with the goal of suppressing Aedes aegypti mosquitoes in the trial site. These mosquitoes can carry dangerous diseases such as Zika, chikungunya and dengue fever.

Oxitec’s male mosquitoes carry a gene that causes their offspring to die well before they can bite anyone and pass on any harmful diseases. In five suppression trials across three different countries, Brazil, Panama, and the Cayman Islands, Oxitec has demonstrated a reduction in local Aedes aegypti populations by over 90% in roughly six months.

Dr. Derric Nimmo is a principal scientist at Oxitec, and is leading the company’s proposed trial in Key Haven. Dr. Nimmo has worked extensively with Oxitec’s OX513A mosquito across the world for over a decade.

We recently caught up with Dr. Nimmo to find out more about how the trial in Florida will work if approved, and what Oxitec is doing to prepare for it.

Q: What is your background, and how did you come to work at Oxitec?

Derric Nimmo: I worked on transgenic insects for about five years as part of my post-doctoral work at Keele University in the UK, studying the basic genetic transformation of the malaria-carrying mosquito species Anopheles gambiae and Anopheles stephensi, as well as the damaging Aedes aegypti species. I was asked to join Oxitec in 2005, to head up the mosquito team. For five years, I was working on our lead strain, OX513A, particularly on mass-rearing [producing millions of genetically engineered insects at a time]. I then moved into field deployment and management of our mosquitoes, and have been working on this ever since.

Q: What else does your work at Oxitec encompass?

DN: In addition to mass rearing, I’ve worked on genetic transformation, biotechnology, and systems to sort mosquitoes. I helped to design a factory we built in Brazil a few years ago, as well as a more recent facility in Florida. In 2009 and 2010, I was heavily involved in trials in the Cayman Islands, and I’ve worked in several other Oxitec field trials as well.

Q: What has been taking up your time most recently?

DN: Since 2010, I’ve been working a lot in Florida as the project lead for a trial we hope to do in Key Haven. I’ve been working on community engagement explaining to a broad range of people how our technology works and what would happen during the proposed trial there.

Q: Walk us through the life cycle of the genetically engineered Oxitec male mosquitoes that you’d be releasing. How would they get from the lab to the wild?

DN: One of the advantages with Aedes aegypti, the mosquito we’re targeting, is that the eggs can be dried and stored for up to six months. It’s one of the reasons that this particular mosquito has been able to transport itself around the world in the past 100 to 200 years. So, we can use that capability to produce eggs in the U.K., where we have stringent quality control.

After producing the eggs, we’d ship them to a facility in Marathon, Florida, where we would rear the Oxitec males before they’re released. It’s about an hour’s drive away from the test site. In the facility, the eggs would be hatched in water, and the larvae put into trays where they’d grow into pupae. Pupae are where the larvae metamorphose into adults, very much like caterpillars becoming butterflies.

The pupal stage is where we do sex sorting, removing the females so that we are releasing males – which don’t bite or transmit disease – into the environment. The male pupae are naturally slightly smaller than the female pupae, and you can use that size difference to sort them in the facility to an extremely high degree of accuracy  using a very finely adjustable sieve that I helped invent.

Once we’ve sorted our males, they go into what we call release pots, which are plastic pots with mesh on top. When the males emerge from the pupae, they fly around in the pots, feed on some sugary solution, and then about three to five days later, we’d load them onto a truck, take them out to the field, open up the lid and release them. The males then disperse very quickly into the environment. There are about 1,000 males per pot, which sounds like a lot, but within a minute after opening the pot and shaking it, they all disappear. We’d repeat that process about three times a week, and over the six to nine months of releases, we would hope to reduce the population of Aedes aegypti in the trial site by more than 90%, as in our previous trials in other parts of the world.

Q: What happens after the genetically engineered mosquitoes are released?

DN: The males have one job to do, and that is to go and find a female, mate with her and pass on their genes. If a female comes across an Oxitec male in the wild and mates with him, her offspring inherit the self-limiting gene from that male and die.

Q: How do you monitor the trial while it’s in progress?

DN: We use a very simple trap – a jam jar or plastic pot that’s half-filled with water and has a wooden paddle placed inside. The females lay their eggs on the paddle just above the water line, and we bring them back to the lab. One of the unique things about our technology is our built in fluorescent marker system. When we bring the eggs back to the lab, we hatch them and look at the fluorescence in the larvae. In every single trial we’ve done so far, when more than 50% of the larvae are consistently fluorescent, we’ve achieved more than 90% control over the mosquito population within roughly six months. But if it’s below 50%, we know we need to release more of our Oxitec males. So, thanks to this technology, we can monitor how well we’re doing in the field on a week-by-week basis in something very close to real-time.

Click here for the second part of the interview, where Dr Nimmo discusses the community engagement work he has been doing in Florida, and explains how the planned trial is being regulated.