Parasites and Clean Water Supplies

25 February 2007

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Clean water is something that many of us take for granted, but Mark Booth describes how in many parts of the world dirty water can lead to life-threatening disease and parasitic infections. To talk about the current strategies in place to supply clean water we are joined by the World Heath Organisation's Alex McKie, and Colin Humphreys explains how high-energy UV LEDs could help provide clean water in the future. In Kitchen Science, Helen Scales and Dave Ansell bring sweetness and light to a house in Cottenham...

In this episode

Barnacles give a Fungal Farewell

A microscopic fungus known as Streptomyces avermitilis could be the solution to a problem that has dogged sailors for centuries. Barnacles attach to the hulls of boat, increasing friction and slowing down the vessels. This leads to increased fuel costs and emissions. At the moment, there are various anti-barnacle treatments that can be used on boats, but they are not very friendly to the environment as the copper-based chemical compounds can leach into the sea and poison marine life. Now researchers at Goteborg University in Sweden have managed to extract a compound from the Streptomyces fungus that is a powerful barnacle killer. When tested as a paint mixture, the paint can keep boats barnacle-free for up to a year. The fungus normally lives in the sea, and releases chemicals as a defence against being eaten. The chemicals are toxic to acorn barnacles and other crustaceans, as even a tiny amount of the toxin affects the animals' nervous systems. One really important finding is that the fungal extract is toxic only as long as the paint is on a painted surface. When the paint is dissolved in sea water, the activation of the poison appears not to take place, making the paint apparently harmless to organisms in the open sea. The researchers think that as little as 0.1% of pure fungal extract is needed to mix into pint to make it barnacle-proof. They are now working to develop their compound into a commercial product.

Making Light of Rapid Virus Diagnosis

Researchers at the University of Georgia, US, have developed a technique for rapidly identifying minute traces of viral genetic material, using just light. The method pioneered by Ralph Tripp and his colleagues makes use of a phenomenon called Raman Spectroscopy. When light hits a surface it scatters, producing a pattern, or Raman spectrum, which is unique to that surface, rather like a fingerprint. The same trick works with genetic material, either DNA or RNA, and so it's possible to tell different viruses apart on the basis of how their genetic material alters the frequency of the scattered light. This was previously well known, but the method couldn't be used in virus detection because the signal it produced was too weak. Now the team have found that by adding tiny silver nanorods to the surface and illuminating them with near-infrared laser light they can make the signal 100 million times stronger, making the system so sensitive that it can detect a single virus particle. It's also extremely quick, requiring only 60 seconds to complete an identification, which means it could easily be used to develop a handheld sensor. "You could apply it to a person walking off a plane to know if they're infected," points out Tripp. The researchers are currently working on an "encyclopaedia" of known viral Raman-shift "fingerprints", so that technicians will know immediately if they are dealing with an unknown virus.

Loud Lizards

Lizards have evolved to play it cool, blending into background foliage to remain hidden from predators. But what do they do when they actually need to get noticed - for example, to attract a mate? New research into lizards has found that the animals "shout" to get noticed against busy leafy backgrounds - but rather than shouting audibly, they use visual tricks. Anole lizards usually signal that a territory is theirs by bobbing their heads up and down. And sometimes,they also inflate their throats to display a large, pink pouch. But these demonstrations can be hard to notice against a distracting background of moving foliage. Researchers from the University of California filmed two species of Anole lizards in Puerto Rico, and found that the greater the visual disturbance in their background (such as moving leaves), the more the lizards bobbed their heads, displayed their pouches and lashed their tails. It's a bit like dancing more and more crazily in a dark nightclub to make an impression on the ladies. The researchers say the lizards need to strike a balance between being showy enough for rivals and mates to pick them out, but subtle enough not to be seen by predators. Similar adaptations have been seen in birds, who literally shout louder to be heard over traffic in busy cities compared to their rural counterparts.

Sweetcorn Solution to Gas Storage

US researchers have found a way to turn corn on the cob leftovers into gas storage tanks for cars running on methane (Liquified Natural Gas - LNG). The problem with LNG tanks is that they are often bulky, heavy, and store gas at very high pressures (over 3600 psi). Instead Peter Pfeifer, from the University of Missouri-Columbia, has found a way to produce a porous carbon matrix capable of storing large amounts of gas at much lower pressures. He first adds corn-cob waste to a solution of phosphoric acid, heats the mixture to over 450°C in a reactor, and then bakes it at 160°C for 3 hours. The product is then washed with water, dried, ground and pressed into briquettes. The resulting carbon matrix contains a network of pores and channels that can soak up 180 times their own volume of methane, but at a very low pressure. Normally methane needs to be stored at pressures of 3600psi, but with this technique 500 psi is needed, allowing designers to build shaped, space-saving lighter tanks. The team are currently road-testing the technique using a pickup truck, which has been using the new system since mid October.

- Parastic LIfe Cycles and Parasitic Infections

Mark talks about some of the more unpleasent creatures that could be sharing your body with you.

Parastic LIfe Cycles and Parasitic Infections
with Dr Mark Booth, University of Cambridge

Chris - Now you're a parasitologist, so how the hell did you get into studying parasites? Did you get some horrendous worm infection as a youngster that got you interested in this or something?

Mark - No it's more academic than that. I was an undergraduate student at Imperial College in London and part of my third year course was all about parasites and I thought ooh, these are rather fascinating creatures.

Chris - But in particular you focus on this thing called schistosomiasis and we'll come to that in just a second. But we say that if you've got lots of parasites around then you must have a healthy population. Is that true?

Mark - Probably not. Lots of parasites certainly are a big problem. Nowadays there's certainly a change in people's thinking in that some parasites may be good for you, but a lot of the parasites are bad for you.

Chris - Now one of the focuses of Mark's work is this thing called schistosomiasis, which is also called bilharzia. It's a highly infectious pathogen and we couldn't possibly bring it into the studio. Part of its life cycle is spent in freshwater snails before it gets into humans, so what we asked Mark to do was to go round with me at his lab at Cambridge University on Friday and show us some of the snails that carry it. This is what we found out.

Mark - We're standing in the schistosomiasis research lab, and we're outside the snail room which is where we keep snails that we use to perpetuate the life cycle of Schistosoma mansoni worms. You'll see right in front of us there's a door with a very orange and red biohazard sign on it. That's because the snails in here are infected and if we were to put our fingers in the tanks where we're keeping the snails, we would also be infected with the worms.

Chris - Shall we have a look at them?

Mark - Let's go.

Chris - Well there are literally rows and rows of tanks full of snails. It's quite dark in here, Mark.

Mark - Yes it's deliberately kept dark because these snails tend to shed the parasite when there is bright light, so we keep them artificially under dim conditions, and when we want to shed them we take them out of the tanks we see in front of us, put them into a small beaker and shine a very bright light on them.

Chris - Why should the parasite want to come out when you put light on the snail?

Mark - That's because under natural conditions, the snail tends to shed the parasite when there are people around. People tend to come into contact with the water during daylight hours, so it helps if the parasite is shed when there are people around and the light is very bright.

Chris - So can we have a look at some of these snails because they're quite small aren't they?

Mark - They are indeed. These are Biomphalaria snails that transmit Schistosoma mansoni. So if you look inside the tank, you'll see that they are very small, maybe about a centimetre wide. These are freshwater snails. You'll see also in the tank that there's some vegetation and these are what the snails feed on.

Chris - So the larvae come out of the snail, burrow through my skin, get into me and then where do they go in my body?

Mark - Well they get passively circulated through the blood system, so essentially when they penetrate the skin they locate a blood vessel and are then circulated via the heart into the lungs. They then elongate and mature in the lungs and then are carried back through the heart. In the liver they then sexually mature and actually end up in the mesenteric veins that link the liver to the gut. That's where they couple and start producing the eggs.

Chris - And how do the eggs find their way back out of the human so they can find another one of those snails?

Mark - Well there's a very good reason why worms are located in the mesenteric veins. That's because they are very close to the gut. When the eggs are laid by the female worm they don't have very far to go: they just have to cross the gut wall and then they're passed out with faecal matter.

Chris - So safe handling of sewage and sewage contaminated water is absolutely crucial in breaking this life cycle and preventing this from happening.

Mark - Absolutely. A high standard of hygiene is required.

Chris - Is it feasible to think that we could stop people becoming infected with these things then?

Mark - There are a number of schemes available. There is a very safe and widely used drug called Praziquantel, which is used in major intervention programmes. The problem with Praziquantel is that it doesn't have any vaccination properties that we know of. So what happens is that people who are treated go out the next day, conduct themselves as normal and they get re-infected. The way to stop people getting infected over the long term is to change their environment and also their habits.

Chris - Well that was us in Mark's lab a couple of days ago. So Mark, it's a big problem schistosomiasis. How many people do you think worldwide are affected with this?

Mark - There's an estimate that about 200 million people are infected, but maybe 600 million people live in an area where they're at risk of infection.

Chris - So it is a pretty major problem. But how does that compare with other major parasite infections worldwide?

Mark - It's somewhere in the middle of the rankings. If we look at some other parasites like the roundworm, that maybe affects about a billion people worldwide, and hookworms 800 million, and trichuris infections a few hundred million as well.

Chris - So you mentioned some of these other worms here, they actually get spread by faecal-oral, in other words people picking up things from the environment, don't they?

Mark - Yes, they're also called soil-transmitted helminths and people become infected when they ingest contaminated soil essentially.

Chris - They don't just have to eat them do they, because don't some of these parasites, like you were saying with schistosomiasis, they can actually drill holes in skin and get in that way. Don't some of these other things do that?

Mark - Yeah the hookworms are particularly good at that. The larvae are shed on the soil and they penetrate the skin when people stand on top of them.

Chris - So tell us a little bit about that because these are worms, so how do they end up going through your skin but migrate to the gut subsequently?

Mark - They're able to penetrate the skin using proteases, which are chemicals that actually melt the tissue away. They then get passively circulated through the blood and they will end up in the lungs. They'll often be coughed up, and when they're coughed up they're swallowed and that's how they end up in the gut.

Chris - And once they get into the gut, how do they survive there?

Mark - They seem to do it very well; they can live for many years. This is one of the great questions that has been asked by researchers: how do they exist in that situation?

Chris - Do they eat our food then, these hookworms?

Mark - Hookworms don't. Hookworms will penetrate the gut lining and drink blood from capillaries.

Chris - And I suppose that you probably started to talk about one particular important thing here, which was that all these things manage to get in through skin, they get into the blood stream, they live in lungs or other tissues and make their way to a final resting place in the gut. So how do they escape the immune system? Why doesn't our immune system attack them and stop them?

Mark - Again, a very good question. There's are a great many researchers interested in answering this question. Essentially it's down to a very sophisticated array of evasion strategies. Some parasites will coat themselves with the antigens of the host so they become almost invisible; some parasites live inside the cells of the host so they're essentially not seen by the immune system; and some parasites will subvert the immune system of the host to the parasite's advantage.

Chris - But haven't some people said that that's really really useful because if we can understand how they do that then we might be able to use this to our advantage to switch off allergy and things.

Mark - Yes. As I said at the beginning, there's now a change in people's perception of what parasites are doing, and it's been suggested that some parasites may be good for you because they do down-regulate some of our more harmful immune responses.

Chris - Now what about some of these other parasites that we see that cause horrible diseases like elephantiasis, people with very swollen limbs. What's going on there?

Mark - Elephantiasis is specifically caused by a filarial nematode and the worms live in lymph nodes. They cause blockage of the lymph nodes and they don't allow lymph fluid to drain properly. Now when that happens you get a process called lymphedema started, which generally affects the lower limbs.

Chris - How do you catch it in the first place?

Mark - Filariasis is transmitted by mosquitoes of the culex genus. The mosquito will bite and then inject a larval form of the filarial worm, which will then mature and migrate to the lymph nodes.

Chris - Now you showed me the other day a picture of someone with a rather nasty lesion on their hand that had a white worm coming out of it, and a matchstick winding the worm up. What was that?

Mark - That was a guinea worm or Dracunculus. That's also a nematode and that was a female worm that I showed you and she's emerging from the skin of that person to lay her eggs. She's formed a blister which is very irritable, so the person would have gone to water to soothe the pain on her skin and the worm will have emerged to lay her eggs in the water.

Chris - So the worm makes the person go into water effectively, and this causes the blister to rupture and the worm escapes.

Mark - Correct.

Chris - So how does another person then recapture that worm or get the parasite in that way?

Mark - The eggs will be ingested by a very small crustacean called a cyclops, it's a copepod, and when people drink unfiltered water they ingest the copepod. The eggs emerge when the copepod dies and they then mature into adult worms.

Chris - Is this something that we might be able to stop because these things are pretty common, you've got lots of people fishing and swimming in all this water in places like Africa, and it sounds like it's going to be a self-perpetuating cycle forever.

Mark - Well guinea worm is one of the few success stories we have against parasitic infections. From a prevalence of about three and a half million people infected just a few years ago, in 2004 the annual number was 16 000.

Chris - So that's a massive reduction isn't it.

Mark - It is, and it's because of the mode of transmission. It's rather easy to intercept by putting muslin cloths over basins and pots for example.

Chris - So education's everything.

Mark - Indeed.

- Is the human bladder like a sponge?

Is the human bladder like a sponge or more like a balloon in the way it holds liquid?

Is the human bladder like a sponge?

The answer is that it's more like a balloon. It's made mostly of smooth muscle and holds all your wee inside. The more you pump into it, the bigger it gets and it's actually quite good to train your bladder because the more you stretch it, the more it gets used to holding things. I don't mean that you should get it to bursting point, but if you can train it so that you don't need to go too soon then it means you have more control later. Many women have problems controlling the muscles when they get older, so a little bit of training is probably quite good.

- Why does cheese make you sweat?

Why does cheese make you sweat? Sometimes if I have too much cheddar, I start feeling sweat creep across my brow. Is this just me?

Why does cheese make you sweat?

The reason I believe that this isn't just you is that there's something that's been known about by pharmacologists for a long time called the cheese reaction. This was first noticed when scientists invented a type of anti-depressant called monoamineoxidase inhibitors, which block up this enzyme monoamineoxidase. This enzyme usually breaks down things that contain amines or nitrogen-containing groups in them. The cheese reaction that people experienced when they ate cheese while on these drugs was that they had very high blood pressure, their heart went very fast and those are all actions of adrenaline. This is because cheese has something in it that acts a bit like adrenaline, and the key one is called tyromine. I wonder whether when you eat a bit of cheese, it stimulates the part of the nervous system that adrenaline would usually stimulate, and thus causes sweating.

- How do mobile phones affect fuel pumps?

How do mobile phones affect fuel pumps, if at all?

How do mobile phones affect fuel pumps?

As far as I'm aware, the answer is that they don't. There was a bit of a scare that mobile phones could spark off an explosion but there's no evidence that they do.

- Why chicken eggs sometimes contain blood?

Could you confirm why chicken eggs sometimes contain blood in them? I thought they were unfertilised.

Why chicken eggs sometimes contain blood?

To a certain extent you can get some red dots in chicken eggs because they've been fertilised, but it's perfectly possible to get red dots and a little bit of blood if they're not fertilised. That's because the egg gets made in the chicken's oviduct. It descends the oviduct and has the shell made around the outside. Sometimes as it's going down the oviduct, a blood vessel in the wall of that oviduct in the mother chicken can burst and spill out and get into the material that's being laid down in the egg. This means that you have a little blood spot in the egg that then gets wrapped up in the shell. Most egg producers shine lights through the eggs in order to see if that's happened and weed them out. Pale eggs are easier to weed out than the brown ones, which is why you tend to see it more often in brown eggs. It's not in any way pathological having the spot in them and you can eat those. They're harmless.

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