Disrupting snail food-chain curbs parasitic disease in Senegal

Benjamin Thompson

Welcome back to the Nature Podcast this week, targeting the snail host of a parasitic disease…

Shamini Bundell

…and the successful launch of India's Chandrayaan-3 lunar mission. I'm Shamini Bundell…

Benjamin Thompson

…and I'm Benjamin Thompson.

<Music>

Benjamin Thompson

First up, reporter Geoff Marsh brings us a story about a battle to control a deadly disease in the fresh waters of Senegal. The first voice you'll hear is researcher Sidy Bakhoum's.

Sidy Bakhoum

So, Dr Sidy Bakhoum, I'm a biologist, I live in Senegal.

<Voices talking and water lapping>

Sidy Bakhoum

Local population every day are in contact with the water. The kids come over there to swim when it is hot, for example, in the summer. So every day they come there. There are some fishermen and others also use the water, for example the farmer to irrigate to grow for example, rice, tomatoes, all those.

Geoff Marsh

In the rural communities of Saint-Louis in Senegal these waterways are a lifeline, and the communities rely on them for washing clothes, growing crops, cooking and drinking, and yes, cooling off in the summer, but it comes at a high risk.

Sidy Bakhoum

So this water can be infected by the parasite schistosomiasis, makes us a lot of problem.

Geoff Marsh

Schistosomiasis is a disease caused by a parasitic worm called a trematode. And it has a huge impact in the tropical world. Here's Jason Rohr. He has been studying ways to combat this disease with Sidy.

Jason Rohr

So it's actually the second most common human parasitic disease in the world behind malaria. Predominantly, it's found in sub-Saharan Africa, about 90% of the cases are found in sub-Saharan Africa, but it's also endemic in southeast Asia and it's also found in Latin America and the Caribbean.

Geoff Marsh

Schistosomiasis can cause a wide range of symptoms and can be highly disabling, causing everything from abdominal pain and diarrhoea to hypertension and problems with learning. In the worst cases, it can be deadly. Treating an individual was schistosomiasis is actually relatively simple using widely available drugs, and yet transmission remains high.

Jason Rohr

The typical way it's combated is with mass drug-administration. The common drug used to treat the disease is called praziquantel. The reason why that's not been very effective is because individuals who receive the treatment do have most of their worms cleared but as soon as they return to a water body, they get reinfected.

Geoff Marsh

Not only are drugs a short-term fix and difficult to achieve in the really rural areas, but with repeated administrations multiple times a year comes an increased likelihood of resistance forming in the parasites. Something needed to change and Jason and Sidy have been working on a fresh approach. But before we get to that, we first need to understand this worm’s complicated lifecycle.

Jason Rohr

So the adult worms reproduce sexually in the human hosts. And those adults will release eggs that are released into the bladder or into the intestines and then are expelled from the human host, either in urine or faeces. Those eggs hatch in freshwater bodies and become miracidia, which is the first free-living larval stage. Those miracidia will swim through the water, searching for a snail intermediate host. If they successfully find a snail intermediate hosts, they will reproduce asexually in the snail and release a second free-living stage called cercariae and the cercariae also will swim through the water like the miracidia but they're searching for the definitive hosts, which are humans. Then if they are fortunate enough to find the skin of the human hosts they'll penetrate the skin of the human host and enter into the circulatory system to eventually end up either in the veins around the intestines or around the bladder depending on the species.

Geoff Marsh

And the the cycle is complete, back to reinfect the human host, but as you just heard that intermediary host was a freshwater snail. And those snails rely on the thick vegetation in these waterways for their habitat and for their food, an algae that lives on the vegetation, which led the team to a simple idea, his Sidy again.

Sidy Bakhoum

if we remove the vegetation, we remove, at the same time, the host, the snail, freshwater snail. So, if this snail is, for example, infected, we remove at the same time also the parasite. No snail, no parasite, yes.

<Voices talking and water lapping>

Geoff Marsh

And so with the help of the local community, that's what they did. And it was a backbreaking effort. Over three years, a whopping total of 432 metric tons of vegetation was removed.

Jason Rohr

Our work was sort of the first large-scale clinical trial where we attempted to remove aquatic vegetation to control the snails and subsequently, human schistosomiasis. And the two treatment arms were vegetation removal or not. All of the children in the schools had their worms treated first. And then we removed the vegetation in half of the villages let the other half as controls. And then we returned and took urine and fecal samples from the children a year later.

Geoff Marsh

The results of Jason and Sidy’s study have been published in Nature this week. And I caught up with them about their findings.

Geoff Marsh

And I suppose the outcomes you were most interested in is first of all, did it have an impact on the snail population? I suppose you can go and count those. And then did that have a corresponding effect on human on schistosomiasis infections?

Jason Rohr

Correct. Yeah, so if I remember correctly, it was yes, there was an eight-fold reduction in snails and a 32% reduction in Schistosoma mansoni prevalence in school children

Geoff Marsh

And there were other benefits too, were there, in that removing all that vegetation increased access for the local communities to the fresh water and safer freshwater?

Jason Rohr

Yes. So, they, the community will go to these water access-points predominantly to get water for washing their clothes for irrigation for cooking purposes. And by removing all this dense, submerged aquatic vegetation, it's much easier for them to put their buckets in to get water for those purposes as well as to swim. So that was one benefit.

Geoff Marsh

Sidy also mentioned to me that there were more benefits from the physical removal of the vegetation from these access points, including boats now able to navigate the waters.

Sidy Bakhoum

Several benefits. More space for travel, because we if we have this, the vegetation, the boat can't cross other side. So if we remove this vegetation, you have more space to move, for the boat and fishermen also have more access in the water.

Geoff Marsh

So lots of different benefits.

Sidy Bakhoum

Yeah, a lot. Yes.

Geoff Marsh

And the gains didn't end there.

Jason Rohr

A lot of the nutrients running off the landscape were being captured by this aquatic vegetation. And so we wanted to return the nutrients captured in this vegetation back to its source ,which was agriculture. And so we tried to convert this public nuisance, this aquatic vegetation into a private resource. And we did that by converting the vegetation into compost and we showed that that compost significantly increased onion and pepper production. And we also converted into livestock feed and we showed that it can be cost-effectively used as livestock feed for sheep, cattle and donkeys.

Geoff Marsh

And when you replace traditional fertilizers with this composted vegetation, how did that compare price-wise?

Jason Rohr

So the economist involved in the project had documented a nearly nine-fold benefit to cost ratio when you included the public-health benefits as well as the agricultural and economic benefits.

Geoff Marsh

You mentioned it was also used as feed for livestock.

Jason Rohr

We showed that if you replace traditional sheep feed with this aquatic vegetation, they maintained weight up to 60% of the replacement And it was up to 141 times cheaper than purchasing feed.

Geoff Marsh

So in a way this approach kills loads of birds with one stone it sounds like. You've got infectious-disease control, better access to food and water, poverty alleviation and environmental sustainability. It sounds like it's achieved a lot with one simple strategy.

Jason Rohr

Yeah. I mean, that was our hope we were trying to identify an intervention that would have multiple wins.

Geoff Marsh

Do you see this being sustainable in the sense that people will carry on doing it?

Jason Rohr

Yes, we hope that it is sustainable. You know, we would regularly have community members come and ask us what we were doing at these water access-points. And we would inform them of what we were doing and why. And in many cases, they volunteered to help us.

Geoff Marsh

What are your plans for scaling?

Jason Rohr

Yeah,great question. So what we've done is we've flown drones, over about 40 different villages, across the seasons now. So that way, we can essentially map where the different species of aquatic vegetation are in these water access-points. And then we're linking that information with satellite imagery of these water access-points. And what that will allow us to do is essentially create a map of where we think schistosomiasis hotspots are in the landscape, which will allow us to target this intervention where we think it's needed the most.

Benjamin Thompson

That was Jason Rohr. You also heard from Sidy Bakhoum, both from the University of Notre Dame in the US. You can find a link to their paper in the show notes. This piece was produced by Geoff Marsh.

Shamini Bundell

Coming up, the bizarre birds’ nests made out of metal spikes. Right now though, it's the Research Highlights with Noah Baker.

Noah Baker

Artificial Intelligence is able to predict which pieces of art are most likely to be remembered. Viewing art is thought to be a subjective experience. But according to new research, a person's memory of an artwork is surprisingly predictable. A team in the US set out to discover which of the museum collection of over 4,000 paintings were most memorable. In one experiment, 19 visitors to the museum were surveyed and asked to which pictures they remembered from their visit. In a second online experiment, more than 3,000 people were shown a series of images and asked to press a key when they recognized an image from earlier in the sequence. And in a third experiment, 40 participants rated paintings based on their perception of things like beauty and how much they were interested by them. The researchers found that participants tended to remember the same paintings. Larger, less cluttered pictures were better remembered than smaller, crowded ones. Perhaps unsurprisingly, people also tended to recall artworks that piqued their interest. Based on these insights a machine-learning model was able to predict which artworks were more likely to be remembered, as well as the relative fame of renowned pieces exhibited in the museum. Read more in the Proceedings of the National Academy of Sciences.

Noah Baker

Supersonic micro-bullets have been softly captured by a new ultra-thin gel. Shock absorbing materials are crucial for protection against strikes from bullets, shrapnel and space debris, but most of them only partially blunt the blow. For example, bulletproof armour deforms and the flesh behind it gets bruised. But this wafer-thin sheet of shock-absorbing gel completely absorbed the blow from microscopic bullets, striking it at four times the speed of sound, leaving no trace on the gel’s aluminium backing. To make the material, a team in the UK incorporated talin, a helical protein found in biological cells in the body talin unfolds to relieve stress when mechanical forces are exerted on cells, averaging them out. Then it refolds when the forces dissipate. In the shock-absorbing gel, the protein does something similar unfolding in trillionths of a second to dissipate high-energy impacts. Supersonic projectiles made of stone tore through a commercial ballistics gel, and made craters in the aluminium behind it. But by contrast, the same projectiles became embedded in a sheet of the talin-based gel that was only five millimetres thick. The bullets themselves also remained undamaged. You can read more in Nature Nanotechnology.

Benjamin Thompson

Finally on the show, it's time for the Briefing Chat, where we discuss a couple of articles that have been featured in the Nature Briefing. Shamini, why don't you go first this week, what have you got?

Shamini Bundell

So we are off to the Moon. I've got a space story that I've been reading a Nature news article about. And it's India's Chandrayaan-3 lunar mission. They're heading for the Moon, and they've launched and the idea is hopefully they will become the fourth country to achieve a controlled landing on the Moon after the United States, the Soviet Union and China.

Benjamin Thompson

I think that word ‘controlled’ is doing a lot of lifting in that sentence, Shamini, maybe we can unpick that later on. But yeah, so Chandrayaan-3 then how did we get to here?

Shamini Bundell

Yeah, Chandrayaan-3, as the name might suggest the third lunar mission. And this is where your comment about a controlled landing comes in. Chandrayaan-2, back in 2019, had some successes and some failures. So the Indian Space Research Organization, they're the ones doing this, the ISRO, they sent an orbiter into orbit with functioning instruments, but they were also trying to put a rover onto the Moon’s surface via lander, and that's the bit that didn't go so well, not exactly a controlled landing. And sadly, their lander crashed just in the final moments of descent. So, they have learnt from that. They are trying again, and there's quite a lot of changes, they’ve made this time to the new lander, which is called Vikram. And it's got a little robotic rover on it called Pragyan. And it's got all sorts of changes. So it's got a few design tweaks, there are new instruments to handle failures, algorithms to deal with unanticipated deviations. And apparently the lander is just sort of bigger and heavier too. So, yeah, I get the impression that they’ve put a lot of effort into hoping that this one won't crash.

Benjamin Thompson

Yeah. Because, you know, we've covered on the podcast several times about how it's those last few 100 feet can really be the most difficult bit in many ways, and it is difficult enough flying all that way. So that's the plan for the mission, then where is it right now then? What's going on?

Shamini Bundell

Yeah, so they've launched on Tuesday, 14th of July. And apparently, the lander is supposed to come down somewhere near the Moon's south pole on the 23rd of August. And then on the lander is this little six-wheeled robot, which is going to wander around near the landing site. I quite like this little nugget from the article, it says it's going to explore the area for one lunar day, which is the equivalent of 14 Earth days.

Benjamin Thompson

Nice. So two weeks rolling on the lunar surface. And assuming all goes, well, then what's the plan? And what's the sort of scientific thrust for this mission?

Shamini Bundell

Well, both the lander and the rover have a bunch of instruments on board, looking at the density of ions and electrons temperature, a seismograph checking for moonquakes. And I think in particular, some of the instruments are potentially more advanced or more sensitive than the ones from previous successful lunar landings. So one scientist quoted said that, you know, hopefully, this mission will help make “some unprecedented measurements of the Moon’s chemical make-up”, so you know, in particular, looking at the elements in the soil and rocks around the landing site, that seems to be something they're particularly interested in.

Benjamin Thompson

And you mentioned that this lander is due to land on the south pole of the Moon. Is that somewhere that's particularly of interest to researchers?

Shamini Bundell

Yes, it's certainly further away from where previous Moon missions have landed, they've tended to be closer to the equator. And the lunar south pole has some sort of interesting features. For example, part of it is permanently in shadow. There are also some big craters near there. So you know, it could have clues towards the composition of the early Solar System. And again, sort of how all of these things formed. And one of the scientists quoted here it says Chandrayaan-3 will provide a close-up view of an entirely new region of the Moon.”

Benjamin Thompson

Well, I guess all eyes will be Moonward in late August, then and we'll see how the Chandrayaan-3 mission gets on and I say it is awfully tricky that last bit. So I'm sure everyone involved is keeping their fingers crossed. But for the time being, let's move on to a story that I read about in The Guardian. And it's kind of wild, really. And it's based on some research that was published in Deinsea, the Annual of the Natural History Museum Rotterdam. And it's all about birds’ nests. And birds are well known for making nests out of all sorts of materials, right, but not just sticks and bits of branch and stuff, the kind of detritus that humanity leaves lying around. But in this work, some birds have taken it one further, and they've made nests out of something that's really supposed to deter them. They’ve turned the tables and they've made nests out of anti-bird spikes.

Shamini Bundell

Oh, I think I saw photos of this. So this is like horrible spikes that's supposed to stop pigeons sitting there and pooing down the building, I guess. How do you make a nest out of that?

Benjamin Thompson

Well you're absolutely right. Yeah, on my way to work this morning here in London, I saw loads of these things, on top of lampposts and buildings and you're right, usually used to keep pigeons away. And in this case, so rather than deterring birds, they've been put to a different use. And our story starts with a PhD student in the Netherlands, Auke-Florian Hiemstra, who is a student that looks at the structures made by animals with a focus on things like plastic pollution, okay, and In this case, they got a message about an interesting looking nest outside a hospital in Antwerp in Belgium, okay, and this is in 2021. And it was on the top of a tree, and it was a magpie nest. And as you say, like it is the most frightening, kind of industrial looking thing you have ever seen. It's spikes in every single direction you can imagine, right. And it turns out that the magpies that made it ripped 50 meters of anti-bird spikes from the roof of the hospital, so 1500 spikes.

Shamini Bundell

Ahh they've just ripped it up from where it is and taken it to a tree.

Benjamin Thompson

Yeah, rather than just finding discarded spikes, they've just removed them and just left behind the glue that was used to keep them on top of the building.

Shamini Bundell

They were just like, ‘we’ll have this’, it looks great to build a nest, how comfy for our little chicks. Why? Is that silly question. Why magpies, why?

Benjamin Thompson

Well, do you know what, it's not a silly question because these nests really fit in with the magpie lifestyle. Okay, so magpies typically when they're making nests out in the open, they build what's called a dome nest, okay, so it has kind of a roof structure to prevent other animals like carrion crows coming in and eating the eggs. They usually pepper, this kind of dome with upward-facing thorns and brambles and stuff like that, right? It's basically spikes. But when they can't find any spikes in kind of an urban environment, what do they turn to? They turned to anti-bird spikes, so they're actually using the anti-bird spikes to deter other birds, which is absolutely fascinating, I think.

Shamini Bundell

I mean, that is what they were designed for. So it's really metal in, sort of, multiple senses of the word. Do you think the magpies make the inside of the nest kind of comfy, at least?

Benjamin Thompson

Well, I do know that in other cases, you know, birds have wedged branches inside anti-bird spikes. This is not on unheard-of behaviour. But in this case, also what’s interesting is this isn't N=1, okay, so as part of this research, they then went out to see could they find any other examples? And the answer is yes, they did. They found four of these other nests, right three made by magpies and one made by crows.

Shamini Bundell

Crows trying to keep away the magpies — we've stumbled into the crow-magpie war here I think.

Benjamin Thompson

Well, who knows, but what these birds have got in common is that they're corvids, okay. And we know that corvids are clever birds. And reading this paper, there's so many interesting facts in here. Corvids have made nests out of you know, human products, I suppose, for a very, very long time. You know, barbed wire back in the 1930s, electrical cables, you name it. Knitting needles as well. So the magpies have been using these as well as the anti-bird spikes. And it shows that that these animals really do have quite a remarkable adaptability. But in terms of this research, there's a great quote from the research behind the paper who says, “Even for me as a nest researcher, these are the craziest birds’ nests I’ve ever seen.”

Shamini Bundell

Good for the birds, maybe not good for the bird-spike installers. So are there any sort of big biological questions that the researchers want to answer?

Benjamin Thompson

Well, yeah, in terms of animal behaviour, there's a few questions to answer here. I mean, for example, are the birds using these spikes, because they're available? Or are they actually intrinsically better than the natural products that they would typically use? Or is it just that they can't find them? How successful is this approach? Are there more nests to find? And will this behaviour spread as well? Because that's something we've discussed on the podcast before about cockatoos in Australia, learning how to get into bins because they learnt from each other. So whether this is kind of the thin end of the wedge, I suppose is an interesting one. But there's so much going on here, I also learned that peregrine falcons use anti-bird spikes to impale their leftover prey and, kind of, come back to it later on. So it seems like there's quite a few birds getting in on the anti-bird spikes. So yeah, next time I'm wandering around central London looking up at these things, I will maybe be looking at them in a slightly different light.

Shamini Bundell

Urban wildlife it’s so cool. I'm 100% gonna be peering around all the trees for corvid nests, and definitely going to keep an eye out for peregrine falcons. Yes, please. Well, thank you very much for sharing that with us, Ben. And they'll be links both of those stories in the show notes, including where you can see some nice photos of these very cool metal bird-spike nests. And you can also sign up for the Nature Briefing, which will bring you a roundup of exciting science stories like these.

Benjamin Thompson

And that's all for this week. If you want to keep in touch with us. You can reach out to us on Twitter, we're @naturepodcast, or you can send an email to podcast@nature.com. I'm Benjamin Thompson.

Shamini Bundell

And I'm Shamini Bundell. Thanks for listening.