Earlier in December I came across this blog entry about the Guinea worm, a parasite you really don't want to be infected with. For more information about it, follow the link in the previous sentence, or this one about efforts by the Carter Center (founded by former US President Jimmy Carter) to eradicate it. The worm relies on humans to complete its life cycle, so there is no reservoir of infection in other species, and infection can be avoided by measures as simple as filtering drinking water through fine cloth; as a result, these efforts have been very successful, reducing the number of cases from 3.5 million in Africa alone in 1986 to less than 5000 (all in a few African countries) in 2008.
It seems likely that before long, Guinea worm disease (or dracunculiasis to use its technical name) will join smallpox to become the second disease to be eradicated worldwide. This will still require a considerable amount of effort and money, as the last few areas where transmission occurs are often poor, remote and politically unstable; the Bill & Melinda Gates Foundation and the UK's Department for International Development recently announced that they were providing 55 million dollars to ensure eradication. Almost everyone, especially people living in areas where the disease used to be a problem, will agree that it will be very good news when the Guinea worm is extinct.
One website takes a different view, however: the Save the Guinea Worm Foundation, which asks 'Why are we willingly destroying an endangered species?', and tries to make the reader feel sorry for the poor little Guinea worms ('It has a nervous system. Its hearts pump blood through its small body', and so on). They even claim to be recruiting volunteers to host Guinea worms and so save them from extinction.
I think this site is intended as a joke (and I suspect that this page is meant to satirize people who maintain that HIV does not cause AIDS) -- let me know if you disagree! However, if you consider the wider question of parasite biodiversity, there is a serious issue -- biodiversity includes all species, not just those that are cute or charismatic (and of course cute or charismatic species may be troublesome to people who live near them). Robert Poulin and Serge Morand in their book Parasite Biodiversity1 estimate that more than 100,000 of the approximately 1.5 million known species are parasites, and that the true number of parasite species is likely to be much higher. They argue that people have a responsibility to conserve all organisms, and cite studies indicating that parasites often play important roles in ecosystems and sometimes turn out to be beneficial to humans (for example, a number of studies indexed in CAB Abstracts suggest that exposure to parasitic worms, or compounds from them, can make allergies less likely).
This2 and other articles by Donald Windsor under the title 'Equal Rights for Parasites' make similar points, and this article describes a particular example: when some rhinoceroses were moved to a safe reserve to protect them from hunting, all their parasites were removed, but it was found that oxpeckers (birds that sit on the backs of rhinos and catch insects) stopped breeding in the absence of large ticks to feed to their young; if they had disappeared as a result, the rhinos would have lost their protection against biting insects.
It's interesting that the last official stocks of smallpox virus, which you might think would be of even less concern to conservationists, have still not been destroyed as far as I know, although this owes more to the fear that unofficial stocks might be used for bioterrorism, and the consequent continued interest in smallpox research, than to any ethical qualms about exterminating a virus.
Of course few will mourn the extinction of the guinea worm, most parasites of humans and common animals aren't in any danger, and conservation of wild animals will automatically conserve many of their parasites too, so I doubt if we will be seeing serious appeals to save parasite species in the near future. But it's probably worth wondering whether killing off everything that (however justifiably) we don't like may sometimes not be an unmixed blessing.
1: Poulin, R. and Morand, S.: Parasite Biodiversity (Smithsonian Books, 2004) ISBN: 1-58834-170-4.
2: Windsor, D.A.: 'Equal rights for parasites'. Perspectives in Biology and Medicine (1997) 40 (2), pp. 222-229
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