I am a graduate of the “Giglioli university of mosquitology” (1969-71). After my studies at the Cayman Islands Mosquito Research and Control Unit under director Marco Giglioli, I became a specialist in mosquitoes and mosquito-borne diseases, working on five continents on a range of nasties: yellow fever, dengue, West Nile, chikungunya, Saint Louis encephalitis and others, plus sorties into malaria, river blindness, ebola and so on. I spent 22 years with the U.S. Centers for Disease Control, including 14 at the CDC Dengue Branch, followed by 12 as Professor at the Pasteur Institute, Paris.
All this is not to thump my drum, but to make clear that over more than four decades I have learned a thing or two about mosquitoes and mosquito control.
And perhaps the most important thing I have learned is that we cannot keep pumping insecticide into the environment and hope to win against the mozzies; we may get an occasional victory but as soon as we congratulate ourselves, we learn they are back!
During my mangrove-roaming days in Cayman, Marco and I tried to think of ways to get rid of the black salt marsh mosquitoes without using insecticides. We hoped that the thermal foggers, ULV machines and eventually aircraft were stop-gaps: in the end, we would gain victory by somehow exploiting weakness in the enemy.
So, are mosquitoes a thing of the past in Cayman? Have you (I nearly wrote we!) been able to get off the insecticide wagon? Obviously not. The MRCU still exists, a far more sophisticated institution with state-of-the-art technology but for the moment, more than four decades after I left, you still have to use insecticide, lots of it.
How many tons of insecticide have been poured onto the land in the islands? How many tons of insecticide have seeped into the shallow soil and eventually into the sea? How many insects other than mosquitoes have had to kick the bucket in order that we get less bites? How has this affected other parts of the ecosystem?
Your biggest problem was always the black salt marsh mosquito but you now have Aedes aegypti, much more famous because it is the most efficient urban vector of yellow fever, dengue, chikungunya and now Zika.
When I was on Grand Cayman, another Giglioli protégé, Mike Nathan, had the task of eradicating Aedes aegypti from the Brac. It had already been wiped out on Grand Cayman and Little Cayman. Mike succeeded (and went on to be the top medical entomologist at the World Health Organization in Geneva, Switzerland).
But aegypti is back! Not only here: In the 1950-60s it was eradicated from much of the Caribbean. It is back everywhere, and stronger than before.
And, as everyone knows, we now have Zika. I knew Zika as an obscure African virus that produced a mild febrile illness with no sequels. Today we all know it can be responsible for hideous deformities in infants, something so appalling that it rivals the most horrific science fiction movie.
Aedes aegypti has been a target of our efforts since 1900, when it was nailed down as the vector of yellow fever. At first, we were successful, we simply eliminated the places that it breeds. But today our urban environment is far too complex. Or rather, our urban environment is far too cluttered with far to much stuff that is a nursery for mosquitoes, stuff we could throw away instead of letting it rot in our yards.
In theory, if we could get rid of those infested containers (surely everyone knows they are the source) we could get rid of the threats of Zika, dengue, chikungunya. But in practice, people … are people.
Now to the point! If we look at the prevalence and incidence of these three viruses worldwide, it doesn’t take much effort to conclude that our methods of control are not worth a hill of beans. Even in Singapore, a tiny island nation where they spend US$30 million a year on dengue control, they still have lots of dengue and chikungunya and now, just recently, Zika.
What all persons in my profession agree is that we spend millions of dollars dumping insecticides on our populations … and still get sick. Our current methods of control … don’t control.
So, there is a desperate need for new and innovative means of attack. At present, there are three major contenders:
- A parasitic bacterium, Wolbachia, that spreads through the mosquito population, supposedly making them less able to transmit viruses;
- An insecticidal hormone called pyriproxyphen that disrupts the metamorphosis of the mosquito larvae; and,
- The transgenic mosquito that Oxitec have produced.
I have tested the Oxitec product in my laboratory in Paris and to me it is a really exciting advance, the most promising of all three.
That is why I am sad, even frustrated, that some people are spreading rumors and anxiety about its use. Here we have a new approach that is effective but does not use toxic insecticides and it is being rejected as “unsafe” by various people.
Here I make a few points:
- People think of a “sterile male” that stops females laying viable eggs. Not so. The males have a small piece of genetic code (a “gene”) that, when mated with a wild female, produce larvae that cannot survive in nature. That code is unique to the mosquito, to Aedes aegypti, not any other species.
- Rumors have been launched that the gene can jump to other insects with the same result. Not so. A mosquito cannot mate with a fly or a butterfly or a bee! So how can the gene jump species?
- Rumors have been launched that, in Brazil, the mosquito gene inserted itself into the gene of the Zika virus and this combination is responsible for the hideous microcephaly. This one is really malicious. First of all, the genes of a mosquito are DNA whereas the virus is RNA; you cannot insert one into the other. Secondly, Zika-associated microcephaly appeared nearly two years before the Oxitec trials in Brazil, in outbreaks in Polynesia, particularly Tahiti, rather a long way from Brazil!
These are the three most common misconceptions over the Oxitec product.
There is also a more generalized fear that all genetically modified organisms are somehow inherently dangerous, despite the fact that nearly all corn and soy grown in the U.S. is genetically modified and that Americans have been eating the stuff for 20 years without problem.
I hope this is of interest and, of course, I hope that the Oxitec trial will eventually go ahead.
Another important reason that I have written at length is that I owe a debt of gratitude to Cayman for having launched me onto a long and fascinating career.