There’s been a lot of reporting about new research about the insect repellent DEET this week. Unfortunately, some of the media didn’t quite get it right. Headlines like this one were common…and completely wrong.
The media coverage left a lot of people confused about DEET, and if it still worked. The results of the research were a lot more nuanced than “DEET suddenly stopped working so we are all screwed.”
Here is what the average person being bitten by mosquitoes needs to know, condensed:
DEET still works fine. It’s still one of the best insect repellents out there. We know a way it might become less effective now, as demonstrated in the laboratory.
The un-condensed version:
DEET is one of our oldest and best insect repellents. It’s universally acknowledged as the best repellent around, and has broad activity against several types of biting flies and ticks. This is why a problem with DEET is big news–it’s invaluable in preventing transmission of several different diseases.
Amazingly, scientists are just beginning to understand how DEET works, even though it’s been in widespread use for 50 years. We know it stops ticks and mosquitoes from biting, but the exact mechanism of how that happens is still not clear. Does it make us ‘invisible‘ by blocking mosquitoes from smelling? Does it smell horrible to biters? It’s still not settled science yet.
That’s important to know, since if we know how something works, we can copy it and try to make new and better controls. There is always a concern with evolution of resistance in insects–they are commonly used to study genetics and mutations for a reason. Insects breed fast, and they breed often–which means that small genetic changes, if they are helpful at keeping a bug alive and having sex, can spread quickly through a population.
Resistance to DEET, our most powerful and broad spectrum insect repellent, would be a very bad thing. And so it makes sense that entomologists interested in human health would be studying how DEET works.
Evidence of genetic resistance to DEET in mosquitoes has actually been around since 1994. In 2010, researchers found that they could increase the frequency of a gene that made mosquitoes ignore DEET to 50% in a couple of generations. That’s alarming, but that was in a laboratory-bred colony.
‘Laboratory-Bred’ is an important distinction for both that study and the recent one. Mosquitoes in a cage have only one source of food (often the hapless graduate student that is rearing them). They can’t fly off and look for other people or animals to bite. It also means that their sexual choices are limited to other mozzies in the cage, so resistance can evolve more quickly that it would out in the wild where they have a wider choice of hookups.
Scientists use work in the lab to model the real world. It helps us understand how organisms grow, change, and respond to their environment. That doesn’t mean that it’s a firm prediction of what will happen out in the larger world, especially with a group as diverse and wily as mosquitoes. That’s why I think headlines like the one at the top are irresponsible, and mangling the message of the research.
You can see an interview with one of the researchers here; note she is careful to repeat that we should not discard DEET wholesale on the results of this research!
“What this work indicates is that there may potentially at some point in the future be some problems with the repellents that we have, that we need to be aware of in advance. Possibly we can use this information to alter the repellent DEET to make it more effective, it may also help us in finding new repellents because we will know if [mosquitoes] are able to overcome certain things……Even though repellents are working fantastically at the moment, what this tells us is maybe how to prevent problems cropping up, and how to alter things for the future to make them more effective.” [emphasis mine]
- CDC list of recommended insect repellents
- Mosquito repellent clothing (uses a different chemical than DEET)
Articles referenced in this post:
- Stanczyk N.M., Brookfield J.F.Y., Field L.M., Logan J.G. & Vontas J. (2013). Aedes aegypti Mosquitoes Exhibit Decreased Repellency by DEET following Previous Exposure, PLoS ONE, 8 (2) e54438. DOI: 10.1371/journal.pone.0054438.t001
- Ditzen M., Pellegrino M. & Vosshall L.B. (2008). Insect Odorant Receptors Are Molecular Targets of the Insect Repellent DEET, Science, 319 (5871) 1838-1842. DOI: 10.1126/science.1153121
- Jaramillo Ramirez G.I., Logan J.G., Loza-Reyes E., Stashenko E., Moores G.D. & Vontas J. (2012). Repellents Inhibit P450 Enzymes in Stegomyia (Aedes) aegypti, PLoS ONE, 7 (11) e48698. DOI: 10.1371/journal.pone.0048698.t003
- Rutledge L.C., Gupta R.K., Piper G.N. & Lowe C.A. Studies on the inheritance of repellent tolerances in Aedes aegypti., Journal of the American Mosquito Control Association, PMID: 8014634
- Stanczyk N.M., Brookfield J.F.Y., Ignell R., Logan J.G. & Field L.M. (2010). Behavioral insensitivity to DEET in Aedes aegypti is a genetically determined trait residing in changes in sensillum function, Proceedings of the National Academy of Sciences, 107 (19) 8575-8580. DOI: 10.1073/pnas.1001313107
Once again, another year has gone by and it’s World Malaria Day. There has actually been a lot of good news in the last few years; overall, deaths and infection have decreased. But.
From the Roll Back Malaria Coalition:
The theme for World Malaria Day 2012 - “Sustain Gains, Save Lives: Invest in Malaria” - marks a decisive juncture in the history of malaria control. Whether the malaria map will keep shrinking, as it has in the past decade, or be reclaimed by the malaria parasites, depends, to a great extent, on the resources that will be invested in control efforts over the next years.
Investments in malaria control have created unprecedented momentum and yielded remarkable returns in the past years. In Africa, malaria deaths have been cut by one third within the last decade; outside of Africa, 35 out of the 53 countries, affected by malaria, have reduced cases by 50% in the same time period. In countries where access to malaria control interventions has improved most significantly, overall child mortality rates have fallen by approximately 20%.
However, these gains are fragile and will be reversed unless malaria continues to be a priority for global, regional and national decision-makers and donors. Despite the current economic climate, development aid needs to continue flowing to national malaria control programs to ensure widespread population access to life-saving and cost-effective interventions.
I have written in past years about some of the really wonderful progress that has been made. Unfortunately, we have controlled all the easy places. Now, as the coalition says in their statement, the gains are fragile.
You might have seen the news a few weeks ago that a drug resistant strain of malaria has arisen in Asia. If malaria becomes resistant to artemisinin, there are no other drugs to treat with. Much of current malaria control relies on a combined 1-2 punch of bed nets and drug treatment. When populations are displaced due to political unrest, or when economies tank and programs are discontinued, those at risk of malaria lose access to medicine and regular housing. Which puts them even more at risk.
The warning note from the RBM Coalition statement I quoted above is repeated in a new paper that came out this week:
Cohen, J., Smith, D., Cotter, C., Ward, A., Yamey, G., Sabot, O., & Moonen, B. (2012). Malaria resurgence: a systematic review and assessment of its causes Malaria Journal, 11 (1) DOI: 10.1186/1475-2875-11-122
The article is a major review of control efforts on multiple continents over the last 80 years. They find that the greatest issue in controlling malaria is economic, not biological:
“Considerable declines in malaria have accompanied increased funding for control since the year 2000, but historical failures to maintain gains against the disease underscore the fragility of these successes. Although malaria transmission can be suppressed by effective control measures, in the absence of active intervention malaria will return to an intrinsic equilibrium determined by factors related to ecology, efficiency of mosquito vectors, and socioeconomic characteristics….
The review identified 75 resurgence events in 61 countries, occurring from the 1930s through the 2000s. Almost all resurgence events (68/75 = 91%) were attributed at least in part to the weakening of malaria control programmes for a variety of reasons, of which resource constraints were the most common (39/68 = 57%). Over half of the events (44/75 = 59%) were attributed in part to increases in the potential for malaria transmission, while only 24/75 (32%) were attributed to vector or drug resistance. ” [emphasis mine]
Nearly all of the 75 resurgence events identified through this review have been ascribed to some aspect of weakening of the malaria control programme, whether because of funding shortages, complacency following successful reductions, or disruptions caused by war or natural disaster. These results suggest that technical problems such as vector resistance appear historically to have been of secondary importance for resurgence to financial and operational factors.”
This research is important, because we need to learn from our failures of the past, not repeat them. The places that are most at risk of malaria are also places where there is political unrest and little budget to support a malaria control program.
This is why “Sustain Gains” is the theme of World Malaria Day this year. We have made amazing progress-but we have in the past, too. Only by sustained effort–funded by everyone–can we continue to progress. Nothing but Nets is trying to supply bed nets to the Sudan–if you can, consider donating!
As an addendum: every time I write about malaria, some pro-DDT trolls show up. From the paper:
One of DDT’s chief advantages is its low cost , and programmes that could no longer use it due to resistance were required to switch to more expensive insecticides, raising the cost of interventions and making them harder to sustain . If, however, resistance to multiple pesticides was the primary driver of resurgence, it would have been extremely difficult to counteract, since vector control, one of the most effective tools available to malaria control programmes, would have proven useless. Instead, however, regions that made a determined effort were able to continue to make gains against malaria despite the obstacle of resistance.
When I was looking up something for last week’s rant, I discovered this map, which shows the progress that has been made in fighting Malaria. Sometimes, I think it’s easy to forget that while a lot remains to be done, there also has been a lot of success. The top map (a) is the extent of malaria in 1900, reconstructed from historic records; the bottom map (b) is the extent of malaria in 2007.
Of course, because this is from a scientific paper, there has to be jargon. To translate: the different colors relate to the level of infection in the general population (PR, or Parasite rate). ”Endemic” means that the infection is maintained in a community at a more or less steady state.
- Epidemic/Unstable means that infections break out periodically in these regions
- Hypoendemic: less than 10% of the population is infected with malaria
- Mesoendemic: between 10% and <50% is infected with malaria
- Hyperendemic: Between 50% and75% is infected with malaria
- Holoendemic: over 75% of the population is infected with malaria
In all but 2% of areas around the globe, malaria infections have declined since the rates before 1968. This graph helps visually show where the difficult to control hot spots are, and also the range of different countries and environments in which malaria can occur.
Full Citation of the paper that is the source of this graphic:
Gething, P., Smith, D., Patil, A., Tatem, A., Snow, R., & Hay, S. (2010). Climate change and the global malaria recession. Nature, 465 (7296), 342-345 DOI: 10.1038/nature09098
I read a lot of strange stuff on the internet. I mean, I’ve covered Extraterrestrial Cows and Mail-order public lice. But I really don’t expect to run into silly conspiracy stuff in Forbes, of all places.
In an article entitled “The Black Death: Longing for the Good Old Days,” James Taylor ties together global warming denialism, DDT boosterism, Edgar Allen Poe, and the Black Death (i.e. Bubonic Plague) to make…a really big pile of something that steams.
He suggests that everything was hunky dory when the climate was hot, but when things got cold–OMGPLAGUE:
“What brought about the Black Death? A thousand years ago, Europe was experiencing a golden age. The fair climate of the Medieval Warm Period, with temperatures similar to or warmer than today’s climate, stimulated bountiful crop production, supported unprecedented population growth,….
Longer winters and cooler, shorter summers decimated crop production throughout Europe. The rains that fell were cold, persistent, and slow to dry up. Famine and plague, which had largely disappeared during the Medieval Warm Period, became the norm rather than the exception. And by 1350, the grim, cold climate brought about the dreaded Black Death.”
He goes on from this to imply that environmentalists want to curb global warming in order to kill us all by bringing back the Black Death. Oh, and malaria, but we’ll get to that part later.
I actually have spent a lot of time over the years researching Bubonic plague, and the 14th century European “Black Death” in particular. I have never read of climate being implicated as a cause for the European plagues. Never.
I would also like to point out that the Little Ice Age actually occurred several hundred years AFTER the period of the bubonic plague outbreaks in Europe. A recent review paper listed the start date around 1570. So, the dots he’s trying to connect, in addition to being unrelated factually, are also unrelated chronologically.
The more interesting theories about why the Black Death was so devastating to Medieval Europe center on increasing urbanization and commerce. In order to have a massive epidemic, you need populations of potential victims to be concentrated. If you get the plague in the middle of nowhere, you will die horribly…and that’s it. There is no one to transmit the plague TO.
On the other hand, if you have concentrations of people in cities and towns; and you have movement of both people and animals between cities and towns, then you have a situation that is ripe for an outbreak. If you add in poor sanitation, it’s a dream for a disease bacterium.
There is a well-documented timeline of outbreaks moving from Asia over to Italy, and then up through Europe. Rats in grain and rats in ships moving from place to place for commerce were probably the primary movers of the disease. (In case you’ve forgotten, fleas are the vector of plague between humans and other animals. In other words, fleas transmit the plague bacteria from infected people/rats to new victims.)
Mr. Taylor is a lawyer working for the Heartland Institute, which advocates for unregulated trade (and also says that cigarettes are harmless). Somehow he seems to have missed the obvious connection between free markets and plague. Hmm.
So, what else? Oh, the Malaria–right. From the article:
“Malaria was becoming a distant memory 50 years ago, but the World Health Organization now reports that over 200 million people contract the disease each year and nearly one million people die from the disease each year. A single, small application of DDT to the inside walls of a hut – in which malarial mosquitoes most frequently infect their victims – will keep malarial mosquitoes at bay for months, but environmental activists have forbidden this chemical infringement on The Natural Condition.”
Let’s start with that first sentence. 50 years ago, Malaria was becoming a memory for the US and Europe; they launched very successful campaigns to control mosquitoes. Malaria eradication was not, however, successful in Africa, Asia, or Latin America. In fact, some areas never were part of any Malarial control campaign. It’s certainly correct to say that too many people die of malaria each year; but it is not correct to say that more die now than in the past. If you look at WHO data for most regions, there is a clear downward trend. Global control of malaria has been slowed by resistance to treatment drugs, as well as mosquito resistance to DDT.
Which brings us to his next claim. In his second sentence, he claims that DDT can be applied to the walls of a “hut” and provide protection from malarial mosquitoes. News flash–not everyone lives in huts–your imperialism is showing. But, hey, let’s run with it.
This is an incorrect statement for a variety of reasons. Indoor Residential Spraying (IRS) is actually not a preferred methodology for the World Health Organization Malaria group; they specifically recommend against using the same chemical year after year. Increased resistance to pesticides is strongly tied to indoor sprays in the report I linked. A quote: ”it is unlikely that universal vector control coverage can be achieved in Africa by IRS alone.”
Taylor’s pollyanna approach ignores the the reality of DDT and malaria in the world today. A hundred countries currently have a malaria problem. It is patently absurd to think that one single chemical (and methodology) can solve a problem that is global in scope.
There isn’t only ONE species of malaria mosquito–there are dozens (And they don’t all bite you when you are inside). There is not just ONE kind of ecosystem in which people and malaria interact. Designing a malaria control methodology has to take into account the political, environmental, and socio-economic situation of a particular community. What, if any, data do we have on the resistance of the mosquitoes to insecticides? It is not a one-size-fits-all problem with one solution.
His last sentence is also untrue. DDT is part of current WHO treatment guidelines. It is not “forbidden”. But DDT is only one piece of a huge, huge complicated problem, and over-reliance on it can actually make things worse by leading to greater insecticide resistance.
What I want to know now is–Why did Forbes let this douche write an article full of BS that was VERIFIABLY FALSE? And what are they going to do about it?
I was interviewed by Drunken Skeptics (Michigan Skeptics Association) about DDT, bed bugs, and my criticism of Brian Dunning for not doing proper research and posting a lot of incorrect stuff about DDT.
I’m actually rather pleased with how it turned out, although you can clearly tell I had a cold. I’m interested in feedback from some of my fellow bloggy entomologists about whether you think I represented the larger entomological community’s views on DDT correctly.
The biggest complaint I have about the whole manufactured controversy surrounding DDT is that it’s a waste of time and energy, and distracts from the real work we need to be doing. DDT boosters like to frame the argument as: “Which is worse, Malaria or DDT?”
They have framed that question so that there is only one possible choice. A forced choice between Malaria and DDT is the WRONG QUESTION. I completely reject that false dichotomy as oversimplification. There are more than two choices.
The real discussion that needs to happen is about the best way to control malaria and improve human health in a particular situation. Over 99 countries have a malaria problem. It is patently absurd to think that one chemical can solve a problem that is global in scope. DDT is part of current WHO treatment guidelines. But it is only one piece of a huge, huge complicated problem.
What is the political, environmental, and socio-economic situation of a particular community struggling with malaria control? What, if any, data do we have on the resistance of the parasite and mosquito vectors to drugs and insecticides? It is not a one-size-fits-all problem with one solution.
Because of the vitriol that is spewed, people like me (and probably a few politicians) are hesitant to talk about Malaria at all. It makes aid to the WHO and Africa a political football that is used to score points. It’s not, really, about DDT at all. It’s about tarring and feathering the environmental movement, and keeping people distrustful of science.
And that is sad.
I’d really like to type up a transcript for the podcast, but I still am under the weather health wise–hopefully I can do that next week.