Science Interviews

Interview

Sun, 13th Nov 2005

Using Parasites To Get Rid of Allergies

Professor David Pritchard, University of Nottingham

Part of the show Parasites, Hookworms and Allergies

Kat - I understand that for your research, you infected yourself with parasites. Tell us about that.

David - This is true. I'm one of ten people who infected themselves with worms.

Kat - Why?

David - We did it because we believe that giving people worms under a controlled regime can benefit people suffering from allergy or auto-immunity.

Kat - I'm just going to bring in Sarah here. What is an allergy?

Sarah - Allergy is actually from the Greek words 'allos' and 'ergos', which means altered reactivity. People that have allergies have immune systems that have increased activity to pollens and things like dust. This causes the common symptoms we think about such as a runny nose, itchy eyes, wheezing, hives or nettle rash type effects. People who have allergies produce an antibody called IgE, which lines our nasal passages and respiratory tract. When people have an allergy to something like pollen, they produce too much IgE, which then binds to histamine receptors on mast cells. The mast cell then pops, releasing lots of histamine, which causes all the symptoms like the itchy nose and eyes. To try and prevent this, people take antihistamine, which binds to the histamine receptors and stops the histamine from getting there. This can prevent an allergic reaction.

Kat - So it's basically our immune system going ver the top. So David, are the kinds of diseases you're looking at like that or slightly different?

David - Well I can add to that by saying that the allergic response actually evolved in people to expel worms. So that's why we have an allergic response. Worms have then developed a response to combat allergy, and it's those strategies that we're trying to harvest to treat disease.

Kat - So what sort of diseases are you looking at?

David - At the moment we're targeting rhinitis for the next pollen season, but we have colleagues in Australia that are targeting Crohn's disease. The idea is that the worm will switch off all hyperactive immune responses.

Kat - What is Crohn's disease?

David - Crohn's is an auto-immune disease that attacks the bowel and causes inflammatory bowel diseases.

Kat - And so how do you think these worms are actually helping?

David - The worms are obviously doing something to the immune system that says, 'stop reacting'. We're trying to harness that property. The main thrust of the lab's aim is to make new drugs from these organisms, but the clinicians in Nottingham have decided to go one step back and use live infection in treating rhinitis sufferers. In January, we are embarking on a study where we'll be infecting cohorts of rhinitis patients with live worms and then monitoring them throughout the hayfever season to see I they assist.

Kat - Can people get on this trial? Can they volunteer to be on it?

David - People have already been recruited, but we do have a contact number if people wanted to be on the trial. However, there's a quite vigorous selection procedure, so they would have to contact us independently.

Mandy - Tell us a little bit more about the worm itself, because people's perception of worms is usually something wriggly! Just before we came on air you showed me a photograph of one and it's not at all as you'd expect.

David - These are quite small worms. They're microscopic to begin with. We've studied these worms in the Tropics for over 20 years, and what we were astonished by was the fact that these worms will live inside you for five years or more despite the fact that there's an immune response to them. They're transmitted to people through the soil. Microscopic worms, transmitted to the soil through faecal matter, will enter the skin, find blood vessels, migrate through the lungs, are coughed up, swallowed and then end up in the small intestine. They will stay there for five years. You don't usually know you have the worms until they reach the gut. Once they reach the gut, if you have too many, you certainly feel that you've got them. During a safety study in Nottingham we were able to establish the safe dose that would get rid of the allergy but not create other symptoms.

Mandy - Now you actually transported these worms through customs by infecting yourselves with them all the way from Papua New Guinea. Presumably you got rid of them.

David - No. My colleague still has them and has been carrying a quite substantial worm burden for five years now.

Mandy - Do they reproduce as well?

David - No, they mate as separate sexes in the small intestine and produce eggs. The eggs pass out in faecal matter and then develop into infective larvae in the soil, which can detect human skin and burrow back through. This is how the cycle is perpetuated.

Sarah - How many worms do you have to give a patient?

David - We've estimated from field studies where worm infection has been linked to a reduction in respiratory wheeze to dust mites, that you can give ten worms to alleviate asthma. Ten worms certainly do not cause any symptoms in recipients. We know this from our safety study. If you go up to twenty five, fifty or definitely with one hundred, you feel sick and have a pain that tells you something is definitely going on in your gut. Saying that, it's not as bad as having gastric flu for example. It's just the uneasy feeling that you have something inside you that perhaps shouldn't be there. However ten can impart benefits. If there are any problems, it's very easy to get rid of them simply by taking drugs similar to those you'd give to your pet.

Sarah - After the worms have gone, do you still have the benefits?

David - It's a good question. In the tropics, people are acquiring worm infections from a very young age. Once children are old enough to move away from their houses, they will start walking on contaminated soil and will pick up worms. These worms will accumulate throughout life. Because they're suppressing the immune system, you tend to gather an increasing worm burden with age. The average worm burden of a person in Papua New Guinea is 25 worms. It's this sort of level that we think is beneficial. Whether we can mimic this in a hospital in Nottingham is difficult to say, because we'll be giving ten worms in one dose after the person has already developed allergy. So the trial may not work this time. We may have to go back to 'trickle infections' where we give small numbers over an increased length of time.

Mandy - What about bringing things like this into the country? Would you need a permit?

David - I think if you bring them in inside you, then no. If you were carrying them in tubes then I think you should declare them. It actually an interesting story. The study being conducted in Australia is using worms taken from Nottingham. However, these worms originated in New Guinea, which as you know is just north of Australia. So these are well travelled worms.

Sarah - It's difficult to know how allergies develop, and we think it's a combination of genes and environment. Maybe if we don't get these worm infestations in the UK anymore, do you think that's playing a role in allergies?

David - There is an hypothesis out there called the hygiene hypothesis, which say that the reason we're so allergic these days is because we live in a very clean environment with thick carpets and dust mites in abundance. By having worms we're reintroducing dirt back into the system. It's a nice idea, although I'm not sure how true it is. We're approaching it from a different angle. Allergic responses definitely occurred to fight worms, so by using them and their products we can turn the system back on itself and switch off allergy.

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