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Diverse roots of human disease

Richard Black | 17:17 UK time, Friday, 23 January 2009

Does loss of biodiversity affect human health?

The United Nations Environment Programme believes it does - the notion was one of the top lines in the last edition of its massive five-yearly Global Environmental Outlook, which came out in 2007.

The nuts and bolts of the link, though, can come across as a bit tenuous - loss of species may affect the discovery of new drugs; biodiversity can impact water quality; and so on. They're not necessarily the most convincing arguments to those who pride themselves on having hard heads.

This week, I came across something a bit more concrete - and what makes it more interesting is that it relates to one of the really poor cousins of the medical research field, schistosomiasis.

Also known as bilharzia, this is a disease which receives so little attention and money that malaria is a rich prince by comparison. Yet it affects about 200m people and is said to be the second most devastating parasitic disease in the world - malaria being the first.

The parasites - flatworms of the genus Schistosoma - spend part of their lives in water-borne snails, and people - usually children - contract the infection from the water when the parasites swim free.

There's no vaccine, and there are really only two modes of attack - either giving regular doses of drugs such as praziquantel, or trying to eradicate the snails that carry the parasite, with chemicals such as copper sulphate.

Some people have looked at introducing crayfish to eat the snails - I hope something of an alarm bell rang there given the problems that invasive species have caused in some places around the world - or by introducing certain plants.

So Pieter Johnson, a researcher at the University of Colorado, asked a simple question; could the diversity of the snail population affect the number of parasites?

Experimental chambersHis team rigged up a series of experimental chambers in their lab. All had the same number of Planorbidae snails that carry the parasites, but he put in different numbers of other snail families that can't carry it.

As he reported in the Royal Society's journal Proceedings B this week, there was a definite impact. The number of Planorbidae infected fell by between a quarter and half when other types of snail were around.

The reason is probably what parasitologists call the "decoy effect". Some parasites will attempt to enter the wrong kinds of host - they can't, they die, and so there are fewer parasites around to infect the real hosts.

Now, this is a laboratory experiment - but if the results do hold true in the wild, here would be both a striking demonstration of the principle that biodiversity can beat disease, and something practical that the millions of people affected by schistosomiasis could use to protect themselves to some extent.

Simply keeping their ponds and streams in a state that preserves the range of native snails might reduce the number of people infected.

Implementing that remedy, however, might not be so straightforward given other environmental trends.

Agriculture is changing in many of the countries affected by schistosomiasis, even in its African heartlands.

Excess fertiliser running off farmland into water stimulates the growth of algae; and this appears to be an advantage to the disease-bearing snails, who can thrive on the green stuff, whereas other types die off.

coral head(It's the same thing in microcosm that's happening to coral reefs; too much nutrition for algae brings the death of important native species - in this case, the coral polyps.)

You could argue, of course, that simply wiping out the wrong kind of snail would be more effective. But it's been tried, it has side effects, and it's a procedure that needs doing time and time again.

And wiping out the hosts wouldn't be an option for another condition where the link from biodiversity to human health has been demonstrated - Lyme disease.

Richard Ostfeld and his collaborators have shown that a diverse ecology reduces the number of white-footed mice, an important carrier of the ticks that transmit the disease.

Lyme disease is frequently in the news in North America, and I'm not surprised, having met a conservationist in Canada a few years ago who was still suffering the effects more than a decade after infection.

Schistosomiasis is rarely in the news anywhere. But it should be; it is one of the factors holding back the health and education of children in the poorest countries, and if simply keeping the right mix of snails alive would indeed help keep the parasite down, why not?

In the meantime, it's not my job to do the UN's publicity; but if they're looking for concrete evidence to show why biodiversity matters to the human race, perhaps the snail-ridden waters of Africa and Asia are places worth looking.


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  • 1. At 7:25pm on 23 Jan 2009, CuckooToo wrote:

    No arguments from me, Richard.

    I'd like to add another reason for trying to maintain biodiversity - the shear joy of seeing such beautiful plants and animals in our lives, the loss of which casts a cloud over all our lives

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  • 2. At 8:37pm on 23 Jan 2009, DavidG wrote:

    While many good things can be said about biodiversity, schisto worm by itself doesn't make a convincing case. Given that its snails are more robust and better fit to survive in changing environment (agricultural run-offs) it's hard to imagine how other "native" species can outcompete or displace them.
    If one thinks of schisto bio-control, predator-fish seems the only viable option so far.

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  • 3. At 01:16am on 24 Jan 2009, manysummits wrote:

    Biodiversity - a modern term, with a decidedly intellectual slant. I was thinking, as I read Richard Black's column, that Earth's ecology is a 'complex system', and we often flounder in trying to understand it rationally.

    Perhaps it is appropriate to remember our emotional, or perhaps spiritual attachment to the planet's diversity, as a poet by the name of Samuel Taylor Coleridge once did in his "Rhyme of the Ancient Mariner":

    "He prayeth best, who loveth best
    All things both great and small."

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  • 4. At 05:30am on 24 Jan 2009, TJ wrote:

    A knowledgeable friend who works in a funding capacity for third world projects says that the top three areas to realize benefits are:
    Clean water supplies.
    Efficient sanitation.
    The rest are icing.
    That is not to detract from the very interesting insights in this article but until these 3 items are addressed it's futile to move forward with any other plans.

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  • 5. At 6:07pm on 24 Jan 2009, bionicjules wrote:

    Very interesting study on snails and the importance of biodiversity. It's the same argument as agricultural pests. They are created by having a monoculture - for instance a field with just one crop. It's a common feature of solving problems in any subject whatsoever: the tendency is to try to change the object which appears to be at the heart of the problem (in this case the snails) but the most powerful method is to change the context - the environment within which the problem occurs. Yet another argument to support permaculture.
    Clean water and good sanitation will reduce the environmental pressures towards a monoculture of snail species, and help break the life cycle of the infective organism. Unfortunately DDT will push populations back towards monocultures, since it will reduce the richness of the biological context.

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  • 6. At 04:16am on 25 Jan 2009, TJ wrote:


    I agree that the wide spread, indiscriminate use of DDT will have the negative effect you describe.
    I should clarify that the use I was referring to was for the controlled use in living quarters.
    What would be your opinion of this?

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  • 7. At 7:58pm on 25 Jan 2009, bionicbadger wrote:

    Promoting diversity as a means to dilute the pool of potential parasite host candidates seems like poor policy. Diversity does not simply stop with the potential hosts for parasites; there is also encouraged diversity in the parasite itself, as it is forced to adapt to changing conditions. This is why I'd be worried that by introducing or promoting biodiversity in such environments, with respect to harmful parasites like schistosomiasis, that we'd be also encouraging diversification of the parasite itself.

    So I'm going to have to agree with Tim Jenvey about effective methods when it comes to human populations and disease vectors: the most effective way to protect populations of humans is to segregate them from the diseases. This segregation usually comes in the form of anti-diversification tactics such as sanitation, elimination of disease from drinking supplies, and the eradication of problem sources (poor irrigation design, etc.). We did not eradicate malaria from North America by *promoting* diversified mosquito populations, but rather by taking a hard-line stance before our methods lost their effectiveness.

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  • 8. At 05:49am on 26 Jan 2009, DavidCrosweller wrote:

    My understanding is that this is partly caused by infected human beings open defecating into waterways. This is just one of the many problems associated with open defecation. We run a charity called Wherever the Need and 60% of our work is now sanitation related. We construct urine diversion eco-sanitation toilets and this breaks the cycle, the parasite is killed and the ensuing compost (and urine) is used in agriculture.

    This solution does not involve the introduction of biodiversity and the ensuing risks, and in my opinion is a more sensible option.

    Hope this helps, David

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  • 9. At 07:40am on 26 Jan 2009, CuckooToo wrote:

    Thank you David, interesting post. Coiuld I ask a question? If 60% of the work is sanitation related, what is the other 40% spent on? I'm not trying to be funny here, I am genuinely interested to find out how much money is spent on administration etc of a typical charity.

    How much is spent on education to try to teach people that crapping in the waterway is not a good idea?

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  • 10. At 07:42am on 26 Jan 2009, CuckooToo wrote:

    Something off topic, but a clear example of the AGW mantra being carried too far:

    In which Jon Jenkins, an Adjunct Professor at Bond University, is sacked for expressing his doubts about AGW - speaks volumns about the new religion

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  • 11. At 2:04pm on 26 Jan 2009, Borisnorris wrote:

    We keep thinking of ways to save human life now, but fail to deal with the problems of over-population which are exacerbated by such action.

    We save lives today so that they can starve tomorrow in an exhausted and depleted environment.

    First deal with the question of feeding and supporting the present ever-growing population.

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  • 12. At 6:20pm on 26 Jan 2009, DavidCrosweller wrote:

    Hello CuckooToo. This is a straightforward answer. We run at about 18% admin cost, therefore 60% of the remainder is spent on sanitation and the balance on water pumps and storage tanks (we believe you have to cover both sanitation and water or else there is a continual cycle of ill health), and livelihoods.

    Did you know that half the hospital beds worldwide are filled with people suffering from intestinal related illnesses. If we dealt with this we would need less money to be spent on health centres and hospitals... Oops sorry, lapsed into a mantra again.

    I cannot comment on other charities, but we are quite efficient.


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  • 13. At 7:03pm on 26 Jan 2009, calcination wrote:

    Cuckootoo- the situation at Bond university does not necessarily correspond with Marohasys claims, given that tim Lambert tried to find out about Jenkins when he made his utterly wrong assertions in the Australian, and couldn't find any evidence for him being at the university at that time:

    At this stage we just have Marohasys word, presumably from Jenkins, for this "sacking", and it would be interesting to see what the university says. Suffice to say, merely sacking someone for speaking out against anthropogenic global warming is wrong; sacking someone for being so incompetent as to make a completely wrong argument would make more sense, although climatology is not Jenkins area of speciality, as you can tell.

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  • 14. At 8:19pm on 26 Jan 2009, ClaphamBusman wrote:

    In the malarial area where I grew up (previous thread) we also had seasonal threats of Bilharzia, due to normal watercourses bursting their banks during the 'long rains'. Whilst we were warned in an adult way about the dangers of playing in the puddles, it was the schoolboy stories of what happens when the worm swims back up your urine stream that really had an effect. Health education, of a sort!
    Personally, I think that these problems require something more urgent than a biodiversity adjustment, and certainly more than some form of diktat from the EU or UN. David Crosweller is closer to the solution when he he promotes 'point of sale' action, at least in the short to medium term.
    I also agree with BorisNorris that we have a major population problem, whether that be with density, growth or overall numbers, but I don't see any short-term solution.

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  • 15. At 8:33pm on 26 Jan 2009, DavidCrosweller wrote:

    Sorry CuckooToo, missed this bit. When you don't have an option you defecate in the most convenient place. You can educate people in the dangers, but unless you provide an alternative then the education comes to nothing.

    You have to remember that the people we work with are not worldly people, they are very simple folk who have little or no education.

    What seems simple to us, is a mountain to them. We are asking them to change patterns that have existed in their community for generations.

    It took us five months to educate a village in Gujurat in the way an ecosan toilet works and why it is different – normally it takes two.

    Hope this helps.

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  • 16. At 07:38am on 27 Jan 2009, CuckooToo wrote:


    Thanks David, I really appreciate your answer. I have said many times that we need to stop wasting money on a problem that probably doesn't exist and address the real issues, such as clean drinking water. My small contribution to this is to always buy ONE water, also a charity, which uses the profits to build roundabouts for kids in third world countries. The roundabouts pump clean water to the surface - the kids have fun, the people get clean water.

    Good luck with your efforts, perhaps your charity should consider constructing reed beds as a way of sanitising the human waste before it hits the rivers?

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  • 17. At 08:54am on 27 Jan 2009, CuckooToo wrote:


    As you say being sacked for an opinion is wrong

    According to Wiki:

    "Until recently Jenkins was at Bond University in Queensland as a lecturer where he worked on the start of the first private medical school in Australia and also in the IT school and he is still an adjunct Professor"

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  • 18. At 5:56pm on 29 Jan 2009, calcination wrote:

    Cuckootwo- looks like the university has a different view on things, as I expected:

    The registrar replied:

    Dr Jenkins was a member of staff here for some considerable time and resigned to enter the NSW Parliament.

    Dr Jenkins was asked to keep an association with University as an adjunct but indicated in 2008 that serious health problems would probably prevent him taking an active role. As a result Dr Jenkins was removed from the adjunct staff listing in 2008. An administrative oversight resulted in Dr Jenkins not being informed of this change in status.

    Assertions that Dr Jenkins has been reprimanded and/or 'dismissed' are without foundation.

    Now, will you take the universities word for it?

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  • 19. At 1:15pm on 30 Jan 2009, CuckooToo wrote:


    so you agree that #13 link was utterly wrong, because clearly the university stated he was an adjunct and, as I said, 2008 is recent.

    #18 says Jenkins was removed in 2008 for being ill, so yes, i believe the university.

    A quote from Dr Jon Jenkins final letter to parliament, which shows he was neither left or right wing, but wanted to defend the little people from big business and government:

    "Power is everything and some are willing to sell or trade any and everything that our forefathers fought for to get it. Whether it's the right to access public land or water sold to developers or traded to extremist Greens for ballot box preferences, whether it's the simple right to fish for food or to ride through the High Country or the more
    fundamental the right of free speech, many of the most precious things have already been lost and we are in danger of
    becoming Aldus Huxley's Brave New World where we live in boxes in bleak cities and all our enjoyment in life is by government; programmed; virtual reality."

    To his final day at the Australian parliament, he was still questioning MMGW

    My turn for the tin-foil hoody, please

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  • 20. At 8:19pm on 14 Mar 2009, asagreenwood wrote:

    I really like what you said about how wailing countries are looking for "a step forward".

    Being able to CATCH as well as GATHER food from the ocean has and is very important.

    Most Sincerely,

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  • 21. At 11:44am on 27 Apr 2009, GianniN wrote:

    Health is wealth...Disease is one of the major problems encountered by human being. In order to avoid the physical disabilities and financial shortcomings that may be brought by it, enough knowledge is necessary. A lot of people are looking to start saving money. Well, CNN has some easy tips to start saving money, and they are simple and very smart. First, pay cash for groceries instead of using a debit card. It sets a concrete limit on funds, and if you keep under budget, it's almost like a payday loan to yourself. Another tip is to use a scooter in lieu of a car for short trips. They are electric, have little upkeep and don't cost much to get. Another good one is to bring your own wine to restaurants. You'll pay for corkage, but a $20 bottle with $5 corkage beats a $40 bottle of theirs. What gets leftover can be used for debt relief if you start saving money.

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