Red teaming and cause area investigation: challenges for screwworm (NWS) eradication

TL;DR: This is a reply to Launching Screwworm-Free Future – Funding and Support Request — EA Forum, Screwworm Free Future is hiring for a Director, and   Animal ASK’s report on Brazil - with a summary of challenges for NWS eradication in South America, such as the existence of large populations of flies (well-adapted to the environment) and relevant information gaps.

Many drafts of this doc were shared and discussed with SFF project team members (as I was myself part of it until recently). Their feedback was remarkably helpful; this text would be way worse without them, and I am grateful for this. We even considered posting as a report authored by the team, but our schedules conflicted a lot, and we couldn’t agree on a final version and deadline. Thus, except for my co-author Fernando Moreno (who attended 5 meetings and shared his thoughts on the issue with me), I decided to assume full responsibility for this report.

My special thanks to carolinaollive (who interviewed Embrapa employees with me),  and the SFF members who read and commented on previous versions of this text: Richard, lroberts, johant, bruce, diegoexposito, Nia, MathiasKB, Aaron Bergman, Johannes Pichler.

Introduction

The term “New World Screwworm” (NWS) refers the parasitic larvae of the fly Cochliomyia hominivorax; they feed on living flesh of warm-blooded animals, causing an infestation called myiasis. It has received a lot of attention because it is a disaster in terms of animal welfare (NWS is arguably more ferocious than other flies causing myiasis^[i]), and it is endemic to South America. It has been successfully eradicated with the Sterile Insect Technique (SIT) from North and Central America – until recently, when new cases started to pop up.

At SFF, we are concerned with the tractability of our project. What follows is a discussion of the potential obstacles we may find in accelerating the eradication of NWS. Thus, here we won’t present reasons for eradication^[ii], as we believe they have been convincingly exposed in Launching Screwworm-Free Future – Funding and Support Request — EA Forum – i.e., especially animal welfare considerations, as NWS is more ferocious than other flies causing myiasis. Also, we’ll expand on our uncertainties and discoveries regarding NWS populations and costs in a future text. Instead here, in the spirit of “red-teaming and adversarial collaboration”, we focus on obstacles for NWS eradication – i.e., arguments for why NWS eradication is possibly not so neglected nor feasible / tractable, at least in the next few decades (unless, of course, new tech breakthroughs show up). Finally, in a more tentative manner, we list some information gaps that could give us a better picture for NWS population control (if not full eradication).

This research is the result of a literature-mapping and a stakeholder consultation. We’ve spent more than 30 hours on this in the last few months, reviewing the literature and talking to experts on farmed animals health, and two researchers working with NWS in the public health system in the Brazilian Northeast region. They displayed conflicting opinions on the feasibility NWS control/eradication projects; we can provide more details, and even share some of our notes, if needed.

Straight to the point:

Neglectedness: as mentioned in the Launching Screwworm-Free Future post, Uruguay is starting an SIT project to eradicate NWS; this is part of a larger proposal, backed by USDA-APHIS (US Department of Agriculture), IAEA (International atomic energy agency) and FAO. Also, Uruguay has already approved that researchers from the Instituto Nacional de Investigacion en Agricultura investigate and test gene drive techniques to eradicate NWS (s. in Spanish, or in English), supported by Institut Pasteur in Montevideo and BID (Inter-American Bank)^[iii], and will be provided with flies by either USDA-APHIS or the Mendoza-based ISCAMEN bug factory. Thus, there are relatively strong players already in the game, which decreases the expected (counterfactual) impact of additional efforts. However, the dispersion of flies should already have started, according to the schedule of the former Administration; it’s likely that the new Administration will de-prioritize this project [iv].

Brazilian officials, and officials from its Southern state of Rio Grande do Sul (a.k.a. RS, where one of us currently live) have been following Uruguay’s SIT project closely. This is because one of the main risks for the Uruguayan eradication project is the reintroduction of NWS from neighboring countries (s. Historical perspective and new avenues to control the myiasis-causing Cochliomyia hominivorax fly in Uruguay). Regarding Argentina, that risk is low, because all of the border is along large rivers. Brazil, on the other hand, has a large dry border with Uruguay along the RS state, and eventual resurgences would likely come from it. Thus, Uruguay is expected to spread sterile flies in RS territory, with Brazilian permission. 

Moreover, Brazil has about half of South America landmass, and more than half of its tropical territory (which is the main NWS original habitat^[v]), so any full eradication project would need to consider Brazil - as argued by Animal ASK’s report. Until we had the meetings mentioned above, we hypothesized that Brazilian officials did not prioritize NWS eradication because they considered it to be either financially costly or politically unattractive, in comparison to other priorities, and that this could be overcome with efficient advocacy efforts. However, our research has given us a better picture of the obstacles to overcome.

Tractability: without stable economic and logistical support of USDA-Aphis^[vi] (which is still funding initiatives in Central America, such as the “Panama wall”), coordinated participation of almost all South American Countries (including Venezuela and French Guayana – though you don’t need Chile, as they are free of NWS) and a (yet non-existent) gene drive product^[vii], full eradication seems very unlikely in the next decades (ep. status: very likely, > .9). Moreover, resurgence of NWS myiasis in previously NWS-free areas shows that: i) success is not guaranteed even if you manage to eradicate C. hominivorax from a large area and keep constant surveillance, and ii) eradication projects might compete for resources; evidence for this is that Uruguay had to postpone its eradication plan because the flies it was going to deploy were instead used to prioritize the Panama barrier to keep other regions NWS-free.

Possible institutional challenges

Currently, we’ve been mapping possible regulatory and legal obstacles. An eradication project will require not only funding and support from governments, but also permits and red tape from different agencies, especially if we deploy gene drives^[viii]. For instance, this would likely require notifying other countries, according to the Cartagena Protocol to CBD.

So far, we have found no authoritative legal source entailing that eradicating NWS would be forbidden: the Convention on Biological Diversity is silent on the matter (s. this paper on parasite eradication) and Brazilian federal environmental law, though usually biased towards non-interference, does allow for pest and synanthropes control in general (see Instrução Normativa 141, de 19 de dezembro de 2006). We’ve found no mention of legal obstacles for the Uruguyan project^[ix].

Another subject to investigate is the possibility of ecological cascading effects. NWS evolved in tropical South America, with the rest of its fauna, where it has a rich genetic diversity, serving as a pollinator (though arguably not a very relevant one, in comparison to other Calliphoridade)^[x], a part of food chains and population control for other species (yeah, by devouring the flesh of animals from inside-out) ^[xi].

We don’t think this is a good argument: we have already changed the environment a lot, and by introducing cattle everywhere, we turned NWS into an uncontrollable synanthrope. Also, there is a lot of redundancies in these biomes (even if not in the precise of niche of “flesh-eating monster”), and there is a paper by Uruguayan researchers arguing that, at least in the Pampas, NWS eradication would probably not have ecological side-effects.

Moreover, NWS is a synanthrope that arguably became more harmful to wild animals because of animal farming – which provides C. hominivoraxwith a steady, accessible and large population of hosts – and is likely to become worse with climate change. Thus, NWS is more similar to a zoonosis that is continuously crossing the boundaries between natural and artificial environments (like influenza, or the extinct Rinderpest) than to examples of native predators disturbing livestock. In addition, current methods for controlling myiasis in livestock entail using huge amounts of insecticides and chemosynthetic products (include antiparasitic drugs, possibly leading to increased resistance of parasites in general), so they already imply relevant social and environmental impacts^[xii].

Natural and geographical challenges

However, it is hard to eradicate native bugs. Consider that SIT usually has a low efficacy; this paper estimates it around 1.7% - i.e., only 1 in 50 sterile males liberated in the environment successfully copulated with at least one female fly. US eradicated NWS by liberating enormous amounts of flies. And it succeeded because NWS wasn’t really adapted to its environment: populations declined starkly in winter^[xiii], and were absent (in the wild) in deserts^[xiv] and swamps.

NWS range in South America - Source (don't worry about the area without NWS reports in the Amazon)

NWS populations are arguably larger in South America: there is less seasonable temperature variation in its abundant tropical rainforests, where flies can easily find food and shelter^[xv]. If you are in the countryside and just leave a bit of bovine liver in a trap rotting under the sun, it’ll soon be covered with C. hominivorax flies. And that’s why we have no data on myiasis prevalence and NWS population in livestock^[xvi]: it is so widespread that nobody (currently) sees any information gain in reporting it – it’s like reporting scratches to the Public Health office. It’s arguably way easier to put some traps outside and statistically infer the size of the NWS population; however, one of our interviewees remarked that requiring compulsory reports of myiasis cases would be important to make the subject more salient and raise awareness about its importance. This would be a huge obstacle for full eradication in the next 20 years: it might be hard to produce enough sterile insects (or even genetically modified insects) to permanently drive NWS populations down. However, it doesn’t mean that parasite control policies couldn’t have large effects.

In summary

We want to emphasize that nothing here implies one should completely give up on NWS control – and even on future eradication. These obstacles are not unsurmountable.

First, on neglectedness: though NWS eradication has been backed by powerful players in the past, future support is not guaranteed. We suspect that a project like SFF, if adequately run, makes NWS eradication more likely than having no wild animal welfare advocates working on this, as it will bring an additional set of considerations, expertise, funding and networks to the table. Right now, there are two fronts we could work on: a) USDA must act to prevent a resurgence of NWS in North America, and ensure it can be eradicated from Central America again; b) in South America, the Uruguyan project may need support (especially if the new Administration is not prioritizing it), and sanitary authorities in Brazil and Argentine should deploy NWS control measures around their border.

Also, researchers should should focus on the existing information gaps. For instance, we would like to know:

1. Are there any review studies on ecological effects of NWS eradication Central America (i.e., a tropical region that could pose as a better comparison for ecological effects in South America)? We have found none.

2. What will be the effects of the Uruguay eradication project? Will it succeed in less than 10 years? Our guess is “yes”, with no observed ecological side-effects. However, unlike the rest of the continent, Uruguay is just plain subtropical Pampas, so this doesn’t extrapolate well to the whole South America – but it’d be evidence that NWS could be controlled at least in the Pampas (where harsh winters and ENSO droughts often drive insects populations down).

3. Would NWS eradication (or milder control initiatives) face legal challenges in any of South American country? And if full eradication faces a legal obstacle, could we instead contain NWS in a (relatively) small area with natural barriers – i.e., in islands, or even in the Amazon region?

4. What is the best recent estimate of C. hominivorax population in South American biomes? in the wild and / or overall? Relatedly: what is the prevalence of NWS myiasis in humans, and farmed and wild animals?

^[i] In the wild, NWS is usually lethal. Unlike other in other types of myiasis, untreated infested wounds do not heal, often get infected, and secrete pheromones that attract other flies; thus, an infested animal will continue so until it dies.

^[ii] Alas, we’ll not consider the hypothesis that future fly factories might be converted for insect farming. This is more of a risk for SIT than for gene drive techniques (as the latter requires fewer insects and factories); besides, we don’t believe this will significantly affect future insect-based food production (in comparison to other features such as public opinion and regulation).

With regards to gene drive research and its potential for dual-use, since bugs are not explicitly mentioned in the Biological weapons Convention (BWC), we spent some time googling about entomological warfare. However, BWC explicitly forbids research on vectors for bioweapons; besides, if bugs themselves are the agents, this would fall under the interpretation fixed in UN’s 1969 A_RES_2603 that ‘any living organisms […] intended to cause disease or death […] which “depend for their effects on their ability to multiply”’ would be as forbidden under the bioweapons ban. Finally, if one is willing to research bioweapons, there are more promising agents than insects. So, we see no evidence that work on this area would imply an increase for WMD risks.

^[iii] Through NWS myiasis is not on the list Disease Eradication - WOAH - World Organisation for Animal Health, WOAH has shown explicit support for its control.

[iv] This has been said to us by a Brazilian researcher working for Embrapa.

^[v] Which is basically anywhere with mammals (there are case studies of myiasis in birds like ostriches, but that seems to be rare – or perhaps it’s just something something selection bias), where the pupae can complete their life cycle – i.e., where the soil doesn’t get too flooded, or too dry, or too cold. So, anywhere North of Patagonia, except for deserts, with seasonal variations in wetlands and semi-arid places.

^[vi] So far, USDA funding for NWS eradication has not been affected by federal budget cuts and disease control has been ranked among Brooke Rollins’s priorities.

^[vii] Researchers linked to Max Scott Lab (and connected to other institutions such as North Carol U or Unicamp) have been for years publishing wonderful results on ways to disrupt NWS genome using CRISPR or techniques that could, e.g., save costs in SIT by producing male-only offspring. Though Uruguay has announced it’s doing research in this area, there is no efficient applicable product in sight.

^[viii] Plus, environmental law is quite different in US and Brazil.

^[ix] We predict that eradication efforts in Brazil would require the agreement of at least the following agencies / departments: Ministry of Agriculture, IBAMA (linked to the Ministry of Environment), ANSN (if we use SIT, we probably need the agency in charge of nuclear safety, but I’m pretty sure that’s the easy part) and ANVISA and CTNBio (linked to Health – if we use GMOs).
We wonder if biodiversity and conservation advocates might eventually oppose NWS extinction – and, in tha case, if it would become a priority for them. For many people, it is OK to eradicate an invasive species, or to control a noxious parasite, but intentionally driving a native insect to extinction is a whole different game. Our interviewees gave mixed answers regarding that: though two of them mentioned that extinction could be harmful on ecological grounds, no one of them thought this would be one of the most challenging issues.

Also, it is sad to say, environmental advocates often lose their battles against the livestock industry; so, eventually, an unreasonable opposition could be defeated, or (best case scenario) it could be circumvented by successful negotiations – if, e.g., the livestock industry could agree to more strict climate change policies in exchange for NWS eradication, as it is arguable that Climate Change Is Worse Than Factory Farming.

^[x] Wikipedia says that only adult males eat “nearby vegetation and the nectar of flowers”, while females “feed on the fluids from live wounds”, but we couldn’t check its Merck Vet Manual source.

^[xi] But why would this cause an imbalance in Brazil if it didn’t cause it in US, considering that NWS was already established there? As we said before, NWS is adapted to Brazil and co-evolved with its flora (which it helps pollinate) and its fauna (where it plays the role of prey and parasite). In US, it provided basically no settled “ecosystem service”; actually, even if it did play a role as, e.g., a pollinator, conservationists would infer that this came at the cost of other native species – e.g., it outcompeted other pollinators, or it favored some types of plants over others. So far no one seems to have found evidence of side-effects of the eradication (s. this and this), but we saw no study claiming this related to Central America, a tropical region. On the other hand, if these non-parasitic ecosystem roles were super important, we could just keep dropping sterile males to provide them.

^[xii] This is a more general problem with public health bureaucracy in general. One of the subjects emphasized in our meetings is that monitoring human and livestock health in Brazil sort of works well up to a point (lots of resources put into that, public databases open to researchers, etc.), but there is no permanent government-sponsored system for monitoring wild animal health – all initiatives are led by researchers and supported by voluntary collaborators. Part of the problem is the usual tragedy of compartmentalized bureaucracies: “wild animal health” is usually understood as under the authority of environmental protection entities, and their expertise and attention is usually in different areas. And that’s why we suspect that promoting “NWS control” as a One Health approach to wildlife disease (as proposed by researchers Jane Capozzelli and Luke Hecht) might be a promising approach here. Brazilian researchers working on myiasis from a public health or a One Heath perspective seem to be favorable to strong control efforts (though they do not mention extinction), and so may end up being valuable allies.

^[xiii] Heat can greatly speed up the life cycle of flies, as anyone who forgot to take the garbage out in the summer will discover by the morning – when the kitchen floor gets crowded with M. domestica maggots.

^[xiv] And here is why Chile is free from NWS: it is a dry country protected by the Andes. Besides, it is famous for its border phytosanitary controls – you can’t even take apples to Chile without a permit.

^[xv] We wrote on SFF first post: “Why are there no C. hominivorax reports in central Amazonas (s. IAEA, slide 12)? Is this due to missing data in remote areas, or could rivers and dense forests act as natural barriers, as the same claim for the Argentina-Uruguay border?”
we spent a lot of time checking maps of that region, but it turns out that the most likely answer to this is “just a gap in notifications, everyone is pretty sure NWS is pervasive in the forest”.

^[xvi] Though myiasis should be reported monthly according to the regulation IN MAPA 50/2013, it’s not even on the form NOTIFICAÇÃO DE DOENÇAS AO SERVIÇO VETERINÁRIO OFICIAL — Ministério da Agricultura e Pecuária