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The New World Screwworm causes tremendous suffering to wild and domestic animals on the South American continent. Gene drives make it possible to eradicate the screwworm and improve the wellbeing of hundreds of millions to billions of wild animals.

I believe political advocacy to coordinate South American countries to use gene drives to eradicate the screwworm looks very tractable and highly impactful in expectation.

In this post I will go over:

  1. Why I believe this to be the case
  2. What the intervention would look like
  3. Beg and plead for someone to go do this

Holy shit, Gene drives

Like many on this forum, I listened to 80k’s podcast episode with Kevin Esvelt, where they discussed using gene drives to eradicate diseases and thought to myself: “holy shit that’s incredible, we should do something” to promptly forget all about it and move on with my life.

Half a year later, when Works In Progress asked me if there was anything I wanted to write about, gene drives popped into my mind. As I started researching for the article, I became increasingly obsessed. Those misfortunate enough to have been around me during this period, have had to endure many long monologues about gene drives.

Throughout my frenzy, I met with Professors, PhDs, and representatives from organisations working on gene drives to eradicate malaria. I’ve now come to the following two conclusions:

  1. Society, at large, should be using gene drives for vector control of endemic diseases such as Malaria. The risks are minute, and the benefits are huge.
  2. Political advocacy for using gene drives to eradicate screwworm in South America, looks incredibly impactful and very tractable.

My article for the magazine (out soon!) is focused on the first point. This forum post is focused on the second.

What is the New World Screwworm?

The  C. hominivorax, or New World Screwworm, is a blowfly, which lays its eggs in the wounds (and other openings, such as the nostrils or ears) of mammals. After hatching, the larvae dig in and begin eating the host alive. The stench left off by the infested wound attracts yet more screwworm flies to lay their eggs. Untreated, 20-80% of animals infected die from the infestation or infections that follow.[1]

Humans, being mammals, are at risk too. Uruguay alone records hundreds of human cases every year.[2]

As one can imagine, being eaten alive by parasites is not much fun. As the scientific literature puts it: “Animals with myiasis may display signs of discomfort, lethargy, weight loss and depression”[3]

To put it as politely: Based on the pictures I have seen, I too would display signs of discomfort if it were me who was infected.

In addition to infecting hundreds of millions of wild mammals, the New World screwworm costs the livestock industry hundreds of millions of dollars every year. To prevent the loss of livestock, North America eradicated the screwworm already in 1960 using the more primitive sterile insect technique.

To prevent the screwworm from migrating back into North America, they additionally worked with Middle American governments to eradicate it there as well, and to this very day they maintain a wall of sterile screwworm in Panama to prevent screwworm from migrating back north.

Since then eradication progress has stalled as the sterile insect technique has proven difficult and expensive to use on the South American continent, where the screwworm is endemic on the majority of the continent.

A survey found that 76% of Uruguayan farmers go as far as to plan yearly animal management around avoiding the screwworm season, to avoid loss of livestock.

In Uruguay alone, farmers lose between 40 to 150 million USD annually[4] (0.14% of the country’s GDP) to screwworm. There is enormous economic interest in seeing it eradicated.

In 2024 Uruguay’s National Institute for Agricultural Research received a $450,000 grant to develop a gene drive for screwworm. Even without the gene drive, Uruguay is interested in using the sterile insect technique to eradicate it within Uruguay, which will require continuously keeping up a costly artificial border of sterile flies insects surrounding the entire country.

What is a gene drive?

In short, the CRISPR/Cas9 Gene drive makes it possible to make a gene edit to an animal that is passed on to every one of its descendants, who in turn pass it on to everyone of theirs. By installing a gene drive into a single animal, over the next generations the gene edit will spread until the entire species has it.

This makes it a rather powerful technology. One way the technology can be used for good, is by driving a gene into an undesirable species which makes the females infertile, causing the population to collapse.

By using gene drives it becomes feasible to eradicate screwworm in South America.

The primary risk[5] from releasing any gene drive for population suppression is how the elimination of the subspecies will affect the surrounding ecology, for example by reducing the food available to predators.

Fortunately that experiment has already been run in North and Central America when they eradicated screwworm decades ago. The environmental impacts were minimal to none. With the reduced need for pesticides, one could even argue the environmental impact was positive.

This hasn’t prevented environmental organisations such as Greenpeace, who are against gene editing of any kind, from lobbying for a global moratorium (ban) on the use of gene drives. The UN voted down this proposal, and gene drives currently exist in somewhat of a legal grey area, where the decision to release any gene drive ultimately rests on individual countries rather than international agreements[6].

The intervention: Political advocacy for governments to release a gene drive

The campaign will likely consist of the following steps:

  • Putting together the coalition supporting a gene drive release.
  • Doing the necessary advocacy to get buy-in from key countries across South America.
  • Playing a coordinating role to connect agencies and get the eradication effort started.

The livestock industry makes up a large part of the economy of many South American countries. As a result, the agricultural lobby is incredibly influential and well connected.

Why is a country such as Uruguay looking to spend so much money on the sterile insect technique to eradicate screwworm in the first place? Hint, it’s not out of concern for the wellbeing of wild animals.

Small scale farmers and industrial factory farmers alike stand to save millions of dollars from the eradication of screwworm.

An effective campaign should put together a coalition of agricultural interest groups and utilise their existing networks and connections to key decision makers. Agricultural departments across countries have a shared interest in seeing it eradicated. Rather than a gene drive release being a national Uruguayan effort, the campaign would work to get other countries to join in and support the effort.

Executed well, I can envision the announcement of a joint programme to eradicate screwworm between several South American countries (perhaps with funding and help from the USDA) by 2030.

The cost-effectiveness of eradicating screwworm

The following sections describe the intuitions behind my cost-effectiveness analysis, feel free to just view it directly and plug in your own numbers.

How many wild animals would it help, and how much?

Eradicating screwworm would save the South American livestock industry hundreds of millions, but between you and me, helping this industry is not what excites me.

The real benefit is to the hundreds of millions of wild mammals in South America, of which I estimate 0.1-4% are infected with screwworm every year.[7] A back of the envelope suggests there are around 89.2 billion wild mammals (plus minus one order of magnitude) on the South American continent. This suggests hundreds of millions or even a few billion animals are infected every year.

Saving them from a painful infection or even death is very motivating to me!

Calculating the welfare improvement for any wild animal welfare intervention is notoriously difficult. If the animals whose lives we save were to later die from something even more painful, we might have done more harm than good. What will be the mammal’s cause of death, if not screwworm?

Eyeballing the estimates from Wild Animal Initiative, I would very roughly say that ~45% of wild mammals die from predation, ~10% from disease, starvation and injuries, ~30% from humans, and 15% from other sources.

Many sources describe screwworm infection as extremely painful, but tracing back the sources I wasn’t able to find any clear root claims. The medical case reports of humans I found did not use many adjectives to describe patients' pain, nor was I able to find any mentions of morphine or other similar strong painkillers being administered for the pain. I imagine a doctor who treats patients with myiasis would have a good sense, but I didn’t have one in my network to ask.

My best guess is that for lethal infections the pain is as bad as that of a severely infected wound, seeing as the causal mechanism of death often is a severe infection following the infestation.

Intuitively it seems worse. If you google: “Screwworm infestation human” you will find upsetting images (please don’t do this unless you’re sure you can stomach it), which gives some idea.

I would personally prefer to be predated, run over by a car, or die from malaria, than I would want to die from a screwworm infection. Having not experienced any of these things, I accept my intuitions may be off, but I don’t know what else to go by. Good chance I’m over indexing on the ‘yuck’ factor of it all.

Using what I think are conservative assumptions, my CEA suggests that eradicating screwworm would constitute a significant improvement to wild animal welfare, with each dollar spent averting suffering equivalent to that of 101 animals dying from screwworm.

The 'gold standard' in animal welfare Corporate Campaigns are estimated to halve the suffering for 66 years of chicken life per dollar spent. These numbers are not directly comparable, but to me screwworm advocacy looks to be in a similar ballpark as the very best animal welfare interventions.

Are gene drives an effective solution?

Unlike the sterile insect technique, which will require weekly releases of millions of screwworms to work, a dozen gene driven screwworms can spread a gene edit far and wide.

Releasing a gene drive in Uruguay would likely result in a temporary substantial reduction in the screwworm population of Uruguay and its neighbours, until screwworms which by chance develop immunity repopulate back. At this point a second gene drive release will be necessary. Rinse and repeat, until the population is extinct.

While the new world screwworm is a single species, it has high genetic diversity across regions. Across the South American continent one can structure the fly into four regional groups of populations, with significant genetic variance. A gene drive released in one region might not spread to the other regions. For lasting and continent wide eradication, I suspect it will be necessary to release gene drives for screwworms in each of these regions.

This is well within what a team of motivated scientists can pull off. Gene drives are likely to be much cheaper, much more effective, and much better for the environment than any other population suppression technique.

What are the costs?

Creating and releasing gene driven screwworms is not by itself too expensive. The R&D costs of developing working gene drives for screwworm will be within the single digit millions at the very highest.

Adding in expenses relating to the test and release, such as environmental reviews and monitoring we get into the tens of millions at most. Most of these costs will be incurred by governments whose counterfactual looks different from that of the EA donor.

The political advocacy itself will perhaps cost a few million dollars, it might even be possible to get the livestock industry to pay for some of it.

The total costs will be in the tens of millions, and only a fraction of that has to come from high counterfactual philanthropic sources. Even without counting welfare benefits, the ROI for governments is positive.

How likely is political advocacy to succeed?

The existing financial interests in seeing screwworm eradicated makes me believe a campaign is much more likely to succeed than it otherwise would be. When you come across an animal welfare intervention that factory farmers are as excited about as you, you should act!

There are few arguments more persuasive to a policy maker than your country’s largest industry saying it would have a high ROI. The harrowing stories of people who have lost friends or relatives to the screwworm can make for effective messaging too.

The timing is also right. In 2024 Uruguay started considering using gene drives, so there is already momentum to latch onto.

I’ve observed that successful EA policy campaigns often fight inertia rather than active and organised opponents. This is unfortunately not the case for this intervention. Environmentalist groups will push back to stop the use of gene drives. I suspect the livestock lobby is the more powerful voice, but who knows.

I believe the most likely outcome is that South America will eventually use gene drives or sterile insect releases to eradicate screwworm anyway, but a coordinated campaign can speed this up by several years.

The ideal founders to pull off this campaign would have familiarity with South American policy and politics. Fluency in Spanish and Portuguese is likely necessary as well.

A call to action

I am not a wild animal welfare researcher and I hope it’s abundantly clear this intervention would benefit from further investigation by someone with domain expertise.

My own estimates suggests policy advocacy to eradicate screwworm to be competitive with the most cost-effective animal welfare interventions.

I am not from South America, I am not well-positioned to work on this, but somebody really should do something. There’s lots to do. One could reach out to the Uruguayan researchers to better understand their bottlenecks. Is it funding? If so, how much? One could speak with the livestock industry to gauge their interest. Would they join a coalition and/or pay for the campaign?

I believe a  group of motivated volunteers could get quite far. If you are interested in continuing work on any of this do reach out. The best person to work on this was someone more qualified five years ago, the second best is you today.

Cochliomyia hominivorax delenda est


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  5. ^

    Some also worry about the gene drive spreading to other Cochliomyia species, which is a genuine concern but not something that worries me that much.

    In theory it could happen through one of two ways:

    - Hybridization (successful cross-breeding between the species)
    - Horizontal spread (gene drive transferred without reproduction, for example through a virus)

    For screwworm I haven't been able to find any source claiming screwworm species can hybridize (unlike between subspecies of eg. anopheles gambiae mosquitoes where it regularly happens). This is in line with what I would expect, as hybridization between species is the exception not the rule. But one could cheaply run a lab experiment to verify they don't hybridize. If nobody has done this already, that would be wise to do.

    Horizontal gene flow is impossible to rule out completely, but the likelihood of this occurring is pretty much zero. The risk of the gene spreading can also be addressed by building the gene drive to target a section of the genome unique to C. hominivorax.

    Additionally one can run a no-payload daisy chain drive test first (more on that in my magazine article) to verify the drive works as intended and doesn't spread, before releasing a full suppression drive.

  6. ^

     Countries which have signed the cartagena protocol have some obligations to their neighbour countries.

  7. ^

     Before the eradication in north America an estimated 2-3% of wild animals in endemic regions were infested: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7789611/#:~:text=Prior%20to%20eradication%20the%20USA,eradication%20%5B17%2C%2018%5D.





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I know this post is a bit of an older post but I question why it needs to be a policy advocacy organization and not a "let's just get this done" organization with some approval by governments with studies done.

I suppose I fear that many people like the allure of policy advocacy because the leverage seems great but in practice there are just a ton of roadblocks at every corner that are lurking when you have to convince corrupt legislators, stagnant and bureaucratic government departments, politicians who mainly care about their re-election/power and looking good short term to voters and more dumb roadblocks.

I am a doctor who has treated patients with myiasis and would love to talk if that helps. As a physician in India, Myiasis as a surgical case is not uncommon, whereas it is unheard of in developed countries (I now know this might be because of the Panama worm-border in North America; previously, I just assumed it was better standards of living). You are not overindexing the 'yuck' factor of it, in fact, dial it up. I can tell a patient has worms in their wounds from over a mile; the stench adds to social stigma for the patient and makes it harder to seek treatment. I remember being the only person in a group of five assigned a patient stepping forward to dress a wound (I won't go into details of how that's done here) because I was the only person not retching uncontrollably. That patient was just an orphan kid who fell, scraped his knee pretty badly a couple of days ago, and never paid attention to the flies because flies are everywhere where he lives. The lethal cases do not differ much from what you would see in a zombie/horror movie. It's just wild to think that in this day and age, there are still people (and animals) being eaten by worms alive.

I wonder if a great additional question here is "How many humans would it help and how much?" Is it the same worm? What is the current estimate of the global disease burden, DALYs? Prima facie, it would seem that it is a slam dunk—kill two birds with a stone— health + animal welfare with a single intervention, but it is not discussed as such yet, which makes me think that either the two don't overlap or just hasn't been looked into it like that. If we assume human suffering gets more policy traction/funding than wild animal suffering, it seems beneficial to explore this.

The 'gold standard' in animal welfare Corporate Campaigns are estimated to halve the suffering for 66 years of chicken life per dollar spent.

IT HALVES THE SUFFERING FOR 66 OF CHICKEN LIFE FOR EVERY SINGLE DOLLAR SPENT??? Wow, just, wow... I'm completely out of words. I had no idea these charities were so unbelievably effective. Can you provide me with some source on that?

I think these numbers are too optimistic and unlikely to be true in 2024, but I don't have a good source for more up-to-date numbers.

THL estimated $2.63 per cage-freed hen in 2022, significantly less effective than 66 years per dollar. And that's an estimate of average cost-effectiveness, not an estimate of the cost-effectiveness of marginal funding (which is likely to be much lower)

The THL estimate is a little strange, I think — the $2.63 is really just their US branch's total 2022 expenses on cage-free campaigns divided by the current number of hens (presently, or at any given time) in the supply chain of companies they persuaded that year. I'm not sure how they are calculating cage-free campaign spend as a proportion of total budget, nor what "persuaded" means (anyone they did outreach to? anyone they secured new commitments from?). Also, the number doesn't account for the fact that once one hen dies, another takes its place in the same living conditions (although the article acknowledges this limitation). So the real value is the delta, in years, between if/when cage-free would have taken hold by default, and when it did/will thanks to their campaign.

Saulius, the author of the RP report that estimates 12-160 chicken-years impacted per dollar spent, says the following as of 3 months ago:

A new estimate would probably output a similar number because reforms have probably gotten less effective, but I now think that I underestimated cost-effectiveness in this report.

Meanwhile Open Phil says the following, about the same report, but referring to marginal opportunities in particular. It's unclear to me if they're thinking of cage-free campaign spend as a "marginal FAW funding opportunity" however.

We think that the marginal FAW funding opportunity is ~1/5th as cost-effective as the average from Saulius’ analysis.


According to research by the Welfare Footprint Project, both of these asks substantially decrease hours in pain experienced by farmed chickens,[2][3] decreasing chicken suffering by an estimated 30%–60%.[4][5]

According to estimates by Šimčikas,[6] corporate campaigns between 2015 and the end of 2018 will improve the welfare of 9 to 120 years of chicken life per dollar spent.

This is the appropriate reaction! I've shared estimates from Saulius' post with people before hoping for a similar one and am disappointed if it doesn't happen. Feeling things scope-sensitively is hard though.

Yes, this seems like an extremely good thing to do and I hope someone takes it on. LEEP and Shrimp Welfare Project seem like good models for what a small team can do.

I am not from South America, I am not well-positioned to work on this, but somebody really should do something. There’s lots to do.

Same, (sadly), but I'd be very happy to donate to such an effort (even something very early stage, pre 501c3 incorporation) and would try my best to get others to donate as well. 

I'd also emphasize that screwworm elimination is the only intervention I know of in its class - that is, an animal welfare intervention with persistent, long-ish term impact. As I wrote in a shortform post a while back:

More, if you think there’s a non-trivial chance of human disempowerment, societal collapse, or human extinction in the next 10 years, this would be important to do ASAP because we may not be able to later.

Seems important to me. 

This would be a nice proof of concept towards hemispheric eradication of aedes aegypti mosquitoes via gene drives. PAHO resolved to attempt hemispheric eradication in 1947, and very nearly succeeded (pdf) with conventional methods, before the program faltered and the hemisphere was re-infested.

Is there a potential insect welfare issue here? The Atlantic article someone posted below talks about 10s of millions of screwworms being dropped a week after being reared.

EDIT: retracted, not an issue with gene drives.

[This comment is no longer endorsed by its author]Reply

Gene drives remove the need to continuously rear and drop screwworms. Counting insect welfare I would wager advocacy for using gene drives looks better not worse.

Oh, yeah, silly of me. Assuming being a screwworm is bad for the screwworm I guess that must be right. Also, I guess I find "but what if the screwworms actually enjoy being screwworms" pretty absurd as an objection to getting rid of them, even if I can't articulate a fully convincing case for why from first principles. 

I'd be happy to provide pro bono consultation on gene drive design. I've written previously about the topic here: https://denovo.substack.com/p/will-no-one-rid-me-of-this-turbulent and https://denovo.substack.com/p/gene-drives-why-the-wait

Imade two prediction markets that are highly related several months ago - kudos to you for doing far more work than me!


This is great, thanks for sharing!
Bad news for the people employed to drop 14.7 million infertile screwworm on the Panama-Columbia border every week though :'(

Good post, thanks for writing! I wonder if you've thought or read much about the ecosystem effects of eliminating the screwworm? 

Executive summary: Political advocacy for using gene drives to eradicate the New World Screwworm in South America appears to be a highly cost-effective intervention that could significantly reduce animal suffering.

Key points:

  1. The New World Screwworm causes immense suffering to hundreds of millions of wild and domestic animals in South America each year.
  2. Gene drives could effectively eradicate the screwworm, and the risks appear low based on past eradication efforts in North and Central America.
  3. An advocacy campaign could coordinate South American governments and agricultural interest groups to implement a gene drive release program by 2030.
  4. Cost-effectiveness analysis suggests each dollar spent could avert suffering equivalent to 101 animals dying from screwworm infestation, competitive with top animal welfare interventions.
  5. Total costs would likely be in the tens of millions, with only a fraction needed from philanthropic sources given the economic benefits to the livestock industry.
  6. While challenges exist, the campaign has a reasonable chance of accelerating eradication by several years, and further investigation by domain experts is warranted.



This comment was auto-generated by the EA Forum Team. Feel free to point out issues with this summary by replying to the comment, and contact us if you have feedback.

Thanks for sharing this! I've really been liking your forum posts recently :) 

Thanks! Very kind of you to say that

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